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Title: Anatomy of the Cat
Author: Jennings, H. S., Reighard, Jacob
Language: English
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Copyright Status: Not copyrighted in the United States. If you live elsewhere check the laws of your country before downloading this ebook. See comments about copyright issues at end of book.

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  Transcriber’s Notes

  Text printed in italics in the source document has been transcribed
  _between underscores_, text printed in bold face =between equal
  signs=. Small capitals have been transcribed as ALL CAPITALS.

  More Transcriber’s Notes may be found at the end of this text.



  ANATOMY OF THE CAT

  BY

  JACOB REIGHARD
  _Professor of Zoology in the University of Michigan_

  AND

  H. S. JENNINGS
  _Instructor in Zoology in the University of Michigan_

  WITH
  _ONE HUNDRED AND SEVENTY-THREE ORIGINAL FIGURES_
  DRAWN BY
  LOUISE BURRIDGE JENNINGS

  [Illustration]

  NEW YORK
  HENRY HOLT AND COMPANY
  1901


  ROBERT DRUMMOND, PRINTER, NEW YORK.



PREFACE.


Although the cat has long been in common use for the practical study of
mammalian anatomy, a clear, correct, not too voluminous account of its
structure, such as should be in the hands of students in the laboratory,
has remained a desideratum. A number of works have been published on the
cat, some of them of much value, yet there is none which fulfils exactly
the conditions mentioned. The books which have appeared on this subject
are the following:

1. Strauss-Durckheim, H. Anatomie descriptive et comparative du Chat. 2
vols. Paris, 1845.

2. Mivart, St. George. The Cat: an Introduction to the Study of
Back-boned Animals, especially Mammals. New York, 1881.

3. Wilder, Burt G., and Gage, Simon H. Anatomical Technology as applied
to the Domestic Cat. New York, 1882.

4. Gorham, F. P., and Tower, R. W. A Laboratory Guide for the Dissection
of the Cat. New York, 1895.

5. Jayne, H. Mammalian Anatomy. Vol. I. Philadelphia, 1898.

The first of these works treats only of the muscles and bones, and is
not available for American students. Its excellent plates (or Williams’s
outline reproductions of the same) should be in every laboratory.

The second book named is written in such general terms that its
descriptions are not readily applicable to the actual structures found
in the dissection of the cat, and experience has shown that it is not
fitted for a laboratory handbook. It contains, in addition to a general
account of the anatomy of the cat, also a discussion of its embryology,
psychology, palæontology, and classification.

The book by Wilder and Gage professedly uses the cat as a means of
illustrating technical methods and a special system of nomenclature.
While of much value in many ways, it does not undertake to give a
complete account of the anatomy of the animal.

The fourth work is a brief laboratory guide.

The elaborate treatise by Jayne, now in course of publication, is a
monumental work, which will be invaluable for reference, but is too
voluminous to place in the hands of students. At present only the volume
on the bones has been published.

As appears from the above brief characterization, none of these books
gives a complete description of the anatomy of the cat in moderate
volume and without extraneous matter. This is what the present work aims
to do.

In the year 1891-92, Professor Reighard prepared a partial account of
the anatomy of the cat, which has since been in use, in typewritten
form, in University of Michigan classes. It has been used also at the
Universities of Illinois, Nebraska, and West Virginia, and in Dartmouth
College, and has proven so useful for college work in Mammalian Anatomy
that it was decided to complete it and prepare it for publication. This
has been done by Dr. Jennings.

The figures, which are throughout original, are direct reproductions of
ink drawings, made under the direction of Dr. Jennings by Mrs. Jennings.

The book is limited to a description of the normal anatomy of the cat.
The direct linear action of each muscle taken alone has been given in
the description of muscles; other matters belonging to the realm of
physiology, as well as all histological matter, have been excluded. It
was felt that the monumental work of Jayne on the anatomy of the cat,
now in course of publication, forms the best repository for a
description of variations and abnormalities, so that these have been
mentioned in the present volume only when they are so frequent as to be
of much practical importance.

Except where the contrary is stated, the descriptions are based
throughout on our own dissections and observations and are in no sense a
compilation. For this reason we have not thought it necessary to collect
the scattered references to the anatomy of the cat that may occur in the
literature. A collection of such references may be found in Wilder and
Gage’s _Anatomical Technology_. In addition to the works already
referred to, we have of course made use of the standard works on human
and veterinary anatomy. Among these should be mentioned as especially
useful the _Anatomie des Hundes_ by Ellenberger and Baum. Other
publications which have been of service in the preparation of the work
are Windle and Parson’s paper _On the Myology of the Terrestrial
Carnivora_, in the Proceedings of the Zoological Society of London for
1897 and 1898, T. B. Stowell’s papers on the nervous system of the cat
in the Proceedings of the American Philosophical Society (1881, 1886,
1888) and in the Journal of Comparative Neurology (vol. I.), and F.
Clasen’s _Die Muskeln und Nerven des proximalen Abschnitts der vorderen
Extremität der Katze_, in Nova Acta der Ksl. Leop.-Carol. Deutschen
Akademie der Naturforscher, Bd. 64.

_Nomenclature._--The question of nomenclature has been one of
difficulty. What is desired is a _uniform_ set of anatomical names,--a
system that shall be generally used by anatomists. At present the
greatest diversity prevails as to the names to be applied to the
different structures of the body. The only set of terms which at the
present time seems to have any chance of general acceptance is that
proposed by the German Anatomical Society at their meeting in Basel in
1895, and generally designated by the abbreviation BNA. This system has
therefore been adopted, in its main features, for use in the present
work. It seems impossible at the present time, however, to impose any
one set of terms absolutely upon anatomists of all nations, and we have
felt it necessary to use for certain familiar structures, in place of
the BNA terms, names that have come to have a fixed place in English
anatomy, and may almost be considered component parts of the English
language. The German anatomists have expressly recognized the fact that
this would be to a greater or less degree necessary among anatomists of
different nations, and have characterized their list as for the present
tentative, and capable of farther development. The only purpose of a
name is that it shall furnish a key to a common understanding; where the
BNA name does not furnish such a key to English readers, and where there
is a term in established English usage that does serve this purpose and
seems unlikely to be supplanted, we have used the latter. But we have
endeavored to make the number of these exceptions as small as possible,
and in such cases we have usually cited at the same time the term
proposed by the German society, followed by the abbreviation BNA. When,
on the other hand, we have adopted a BNA term for which there is also a
commonly used English equivalent, the latter has likewise usually been
cited in parenthesis.

In deciding whether or not to use in a given case the BNA term many
difficult cases arose. Will the common English name _innominate_ bone
(os innominatum) be replaced by the BNA term _os coxæ_ or _coxal bone_?
We have held this to be highly improbable, and have therefore used the
term _innominate bone_, merely citing _os coxæ_ (BNA) as a synonym. In
the same way we have used _centrum_ as a designation of a part of a
vertebra, in place of _corpus_ (BNA); _premaxillary_ bone or
_premaxilla_ in place of _os incisivum_ (BNA); _malar_ bone in place of
_os zygomaticum_ (BNA); _trapezoid_ as a name of one of the bones of
the carpus, in place of _os multangulum minus_ (BNA), etc. In other
cases where it has seemed probable that the BNA term would come into
common use, though now unfamiliar, this and the more common English
expression are both used or used alternatively; such has been the case,
for example, with the Gasserian ganglion or semilunar ganglion (BNA). In
naming the cerebral sulci and gyri the system in use for man is not well
fitted for bringing out the plan of those in the brain of the cat, so
that it was necessary to reject the BNA names for these structures.

As to the use of the Latin terms and their equivalents in English form,
we have made a practice of employing in the text sometimes one,
sometimes the other; this has the advantage of giving variety, and of
impressing the interchangeability of the Latin and English forms on the
mind of the student. Where a given structure is called by two equally
well-known names, we have used both, holding that the student should
become familiar with each and recognize their identity of meaning.

In general we have maintained the principle that the primary purpose of
such a work as the present is not to illustrate or defend any particular
system of nomenclature, but to aid in obtaining a knowledge of the
structures themselves. With this end in view, we have used such terms as
would in our judgment best subserve this purpose, making the BNA system,
as the one most likely to prevail, our basis. In applying the system we
have had to keep in mind a number of sometimes conflicting principles.
In some cases the judgment of other anatomists will doubtless differ
from our own; but this we feel to be inevitable. The matter of an
absolutely uniform nomenclature is not ripe for settlement at the
present time.

Some further explanation is needed in regard to the topographical
terms, or terms of direction, used in the present work. We have adopted
the BNA terms in this matter also. The terms _superior_, _inferior_,
_anterior_, and _posterior_ have been avoided, as these terms do not
convey the same meaning in the case of the cat as they do in man, owing
to the difference in the posture of the body. In place of these terms
are used _dorsal_ and _ventral_, _cranial_ and _caudal_. As terms of
direction these, of course, must have an absolutely fixed meaning,
signifying always the same _direction_ without necessary reference to
any given structure. For example, _cranial_ means not merely toward the
_cranium_, but refers to the _direction_ which is indicated by movement
along a line from the middle of the body, toward the cranium; after the
head or cranium is reached, the term still continues in force for
structures even beyond the cranium. Thus the tip of the nose is
considered to be _craniad_ of the cranium itself. _Lateral_ signifies
away from the middle plane; _medial_ toward it. _Inner_ and _outer_ or
_internal_ and _external_ are used only with reference to the structure
of separate organs, not with reference to the median plane of the body.

In describing the limbs the _convexity_ of the joint (the elbow or knee)
is considered as _dorsal_, the concavity being therefore ventral.
_Medial_ refers to that side of the limb which in the normal position is
toward the middle of the body; _lateral_ to the outer side. Terms of
direction which are derived only from the structure of the limb itself
are in some cases more convenient than the usual ones. In the fore limbs
the terms _radial_ (referring to the side on which the radius lies) and
_ulnar_ (referring to the side on which the ulna lies) are used; in the
hind limbs the terms _tibial_ and _fibular_ are used in a similar
manner. _Distal_ means toward the free end of a limb or other projecting
structure; _proximal_, toward the attached end.

For all these terms an adverbial form ending in _-ad_ has been employed.
Experience has shown this to be very useful in practice, and while not
expressly recommended by the BNA, it is not condemned. Terms ending in
_-al_ are therefore adjectives; those ending in _-ad_ are adverbs.

In compounding these terms of direction, the hyphen has been omitted in
accordance with the usage recommended by the Standard Dictionary. Thus
_dorsoventral_ is written in place of _dorso-ventral_, etc. The student
will perhaps be assisted in understanding these compounds if he notes
that the first component always ends in _-o_, so that the letter _o_
practically serves the purpose of a hyphen in determining how the word
is to be divided.

In one particular the BNA nomenclature is not entirely consistent. While
recommending or at least permitting the use of the general terms
_dorsal_ and _ventral_ in place of the human _posterior_ and _anterior_,
and _cranial_ and _caudal_ in place of _superior_ and _inferior_, it
retains the words _anterior_, _posterior_, _superior_, and _inferior_ as
parts of the names of definite organs. For example, we have the muscle
_serratus anterior_ in place of _serratus ventralis_; _serratus
posterior inferior_ in place of _serratus dorsalis caudalis_. This is
very unfortunate, from a comparative standpoint, but we have felt it
necessary to retain the BNA terms in order that the structures of the
cat may receive the same names as the corresponding structures of man.

In the matter of orthography we have endeavored to follow the best
English anatomical usage, as exemplified in Gray’s _Human
Anatomy_,--therefore writing _peroneus_ in place of _peronæus_,
_pyriformis_ in place of _piriformis_, etc.

The book is designed for use in the laboratory, to accompany the
dissection and study of the structures themselves. Anatomy cannot be
learned from a book alone, and no one should attempt to use the present
work without at the same time carefully dissecting the cat. On the other
hand, anatomy can scarcely be learned without descriptions and figures
of the structures laid bare in dissection, so that this or some similar
work should be in the hands of any one attempting to gain a knowledge of
anatomy through the dissection of the cat.

The figures have all been drawn from actual dissections, and have been
carefully selected with a view to furnishing the most direct assistance
to the dissector. It is hoped that no figures are lacking that are
required for giving the students the necessary points of departure for
an intelligent dissection of any part of the body. The fore limb is
illustrated somewhat more fully than the hind limb, because it was
thought that the fore limb would usually be dissected first; the hind
limb will be easily dissected, with the aid of the figures given, after
the experience gained in dissecting the fore limb.

As the book is designed to accompany the dissection of the specimen in
the laboratory, it was deemed best to give succinct specific directions
for the dissection of the different systems of organs, together with
suggestions as to methods of preserving and handling the material. These
are included in an appendix.



CONTENTS.


                                                                    PAGE
  THE SKELETON OF THE CAT                                              1

    I. The Vertebral Column                                            1
      Thoracic Vertebræ                                                1
      Lumbar Vertebræ                                                  7
      Sacral Vertebræ: Sacrum                                          8
      Caudal Vertebræ                                                 11
      Cervical Vertebræ                                               11
      Ligaments of the Vertebral Column                               16

    II. The Ribs                                                      18

    III. The Sternum                                                  20

    IV. The Skull                                                     21
      Occipital Bone                                                  22
      Interparietal                                                   25
      Sphenoid                                                        25
      Presphenoid                                                     29
      Temporal                                                        30
      Parietal                                                        36
      Frontal                                                         37
      Maxillary                                                       39
      Premaxillary                                                    41
      Nasal                                                           42
      Ethmoid                                                         42
      Vomer                                                           44
      Palatine                                                        45
      Lachrymal                                                       46
      Malar                                                           47
      Mandible                                                        47
      Hyoid                                                           49
      The Skull as a Whole                                            49
      Cavities of the Skull                                           57
      Joints and Ligaments of the Skull                               61

    V. The Thoracic Extremities                                       62
      Scapula                                                         62
      Clavicle                                                        64
      Humerus                                                         64
      Radius                                                          67
      Ulna                                                            68
      Carpus                                                          69
      Bones of the Hand                                               71
      Joints and Ligaments of the Thoracic Limbs                      73

    VI. The Pelvic Extremities                                        76
      Innominate Bones                                                76
      Femur                                                           79
      Patella                                                         80
      Tibia                                                           80
      Fibula                                                          82
      Tarsus                                                          82
      Bones of the Foot                                               85
      Joints and Ligaments of the Pelvic Limbs                        86


  THE MUSCLES                                                         93

    I. Muscles of the Skin                                            93

    II. Muscles of the Head                                           96
      _A._ Superficial Muscles                                        96
      _B._ Deep Muscles                                              107
        _a._ Muscles of Mastication                                  107
        _b._ Muscles of Hyoid Bone                                   112

    III. Muscles of the Body                                         115
      1. Muscles of the Back                                         115
        _A._ Muscles of the Shoulder                                 115
        _B._ Muscles of the Vertebral Column                         123
          _a._ Muscles of the Lumbar and Thoracic Region             126
          _b._ Dorsal Muscles of the Cervical Region                 131
        _C._ Muscles of the Tail                                     136
      2. Muscles on the Ventral Side of the Vertebral Column         138
        _A._ Lumbar and Thoracic Regions                             138
        _B._ Muscles on the Ventral Side of the Neck                 139
      3. Muscles of the Thorax                                       144
        _A._ Breast Muscles (Connecting the Arm and Thorax)          144
        _B._ Muscles of the Wall of the Thorax                       148
      4. Abdominal Muscles                                           153

    IV. Muscles of the Thoracic Limbs                                156
      1. Muscles of the Shoulder                                     156
        _A._ Lateral Surface                                         156
        _B._ Medial Surface                                          161
      2. Muscles of the Brachium or Upper Arm                        164
      3. Muscles of the Antibrachium or Forearm                      172
        Fascia of the Forearm                                        172
          _A._ Muscles on the Ulnar and Dorsal Side of the Forearm   173
          _B._ Muscles on the Radial and Ventral Side of the Forearm 179
      4. Muscles of the Hand                                         184
        _A._ Between the Tendons                                     184
        _B._ Muscles of the Thumb                                    184
        _C._ Between the Metacarpals                                 185
        _D._ Special Muscles of the Second Digit                     185
        _E._ Special Muscles of the Fifth Digit                      185

    V. Muscles of the Pelvic Limbs                                   186
      1. Muscles of the Hip                                          186
        _A._ On the Lateral Surface of the Hip                       186
          Fascia of the Thigh                                        186
        _B._ On the Medial Surface of the Hip                        192
      2. Muscles of the Thigh                                        194
      3. Muscles of the Lower Leg                                    203
        _A._ On the Ventral Side                                     203
        _B._ On the Dorsal and Lateral Surfaces                      209
     4. Muscles of the Foot                                          212
        _A._ Muscles on the Dorsum of the Foot                       212
        _B._ Muscles on the Sole of the Foot                         212
        _C._ Muscles of the Tarsus                                   215


  THE VISCERA                                                        217

    I. The Body Cavity                                               217

    II. Alimentary Canal                                             221
      1. Mouth                                                       221
        Glands of the Mouth                                          223
        Teeth                                                        224
        Tongue                                                       226
        Muscles of the Tongue                                        228
        Soft Palate                                                  229
        Muscles of the Soft Palate                                   230
      2. Pharynx                                                     231
        Muscles of the Pharynx                                       232
      3. Œsophagus                                                   234
      4. Stomach                                                     234
      5. Small Intestine                                             236
      6. Large Intestine                                             237
      7. Liver, Pancreas, and Spleen                                 239

    III. Respiratory Organs                                          243
      1. Nasal Cavity                                                243
      2. Larynx                                                      246
        Cartilages of the Larynx                                     247
        Muscles of the Larynx                                        249
      3. Trachea                                                     251
      4. Lungs                                                       252
        Thyroid Gland                                                254
        Thymus Gland                                                 254

    IV. Urogenital System                                            255
      1. Excretory Organs                                            255
        Kidneys                                                      255
        Ureter                                                       256
        Bladder                                                      256
        (Suprarenal Bodies)                                          257
      2. Genital Organs                                              257
        _A._ Male                                                    257
        _B._ Female                                                  263
        Muscles of the Urogenital Organs, Rectum, and Anus           268
          _a._ Muscles Common to the Male and Female                 268
          _b._ Muscles Peculiar to the Male                          271
          _c._ Muscles Peculiar to the Female                        272


  THE CIRCULATORY SYSTEM                                             274

    I. The Heart                                                     274

    II. The Arteries                                                 280
      1. Pulmonary Artery                                            280
      2. Aorta                                                       281
        _A._ Thoracic Aorta and its Branches                         281
          Common Carotid Artery                                      283
          Subclavian Artery                                          290
        _B._ Abdominal Aorta and its Branches                        301
          External Iliac Artery and its Branches                     309

    III. The Veins                                                   315
      1. Veins of the Heart                                          315
      2. Vena Cava Superior and its Branches                         316
        Veins of the Brain and Spinal Cord                           324
      3. Vena Cava Inferior and its Branches                         325
        Portal Vein                                                  326

    IV. Lymphatic System                                             330
      1. Lymphatics of the Head                                      331
      2. Lymphatics of the Neck                                      332
      3. Lymphatics of the Thoracic Limbs                            332
      4. Lymphatics of the Thorax and Abdomen                        333
      5. Lymphatics of the Pelvic Limbs                              334


  THE NERVOUS SYSTEM         335

    I. The Central Nervous System                                    336
      1. Spinal Cord                                                 336
      2. The Brain                                                   339
        (1) Myelencephalon                                           344
        (2) Metencephalon                                            347
        (3) Mesencephalon                                            351
        (4) Diencephalon                                             352
        (5) Telencephalon                                            357

    II. The Peripheral Nervous System                                369
      1. Cranial Nerves                                              369
        I. Olfactory Nerve                                           369
        II. Optic Nerve                                              369
        III. Oculomotor Nerve                                        369
        IV. Trochlear Nerve                                          370
        V. Trigeminal Nerve                                          370
        VI. Abducens                                                 375
        VII. Facial Nerve                                            375
        VIII. Auditory Nerve                                         377
        IX. Glossopharyngeal Nerve                                   378
        X. Vagus Nerve                                               378
        XI. Accessory Nerve                                          382
        XII. Hypoglossal Nerve                                       383
      2. Spinal Nerves                                               383
        _A._ Cervical Nerves                                         383
          The Brachial Plexus                                        386
        _B._ Thoracic Nerves                                         393
        _C._ Lumbar Nerves                                           394
          Lumbar Plexus                                              395
        _D._ Sacral Nerves and Sacral Plexus                         399
        _E._ Nerves of the Tail                                      404
      3. Sympathetic System                                          404


  SENSE ORGANS AND INTEGUMENT                                        409

    I. The Eye                                                       409

    II. The Ear                                                      415

    III. Olfactory Organ                                             426

    IV. Organ of Taste                                               426

    V. Integument                                                    427


  APPENDIX: PRACTICAL DIRECTIONS                                     429


  INDEX                                                              473



LIST OF ILLUSTRATIONS.


  FIG.                                                              PAGE

    1. Skeleton                                                        2
    2. Fourth Thoracic Vertebra                                        3
    3. Fourth Thoracic Vertebra                                        3
    4. Thoracic Vertebræ                                               5
    5. Lumbar Vertebræ                                                 7
    6. Sacrum                                                          9
    7. Sacrum                                                          9
    8. Caudal Vertebra                                                11
    9. Caudal Vertebra                                                11
   10. Cervical Vertebræ                                              12
   11. Sixth Cervical Vertebra                                        13
   12. Atlas                                                          13
   13. Axis                                                           15
   14. Ligaments of the Odontoid Process                              18
   15. Rib                                                            19
   16. Sternum                                                        20
   17. Occipital Bone                                                 22
   18.    Occipital Bone                                              22
   19. Interparietal                                                  25
   20. Sphenoid                                                       25
   21. Presphenoid                                                    29
   22. Temporal                                                       31
   23.    Temporal                                                    31
   24. Tympanic Bulla                                                 33
   25. Petrous Bone                                                   34
   26. Frontal                                                        37
   27. Maxillary Bone                                                 39
   28. Maxillary Bone                                                 39
   29. Premaxillary                                                   41
   30. Nasal                                                          42
   31. Ethmoid and Vomer                                              43
   32. Ethmoid and Vomer                                              43
   33. Palatine                                                       45
   34. Lachrymal                                                      46
   35. Malar                                                          46
   36. Mandible                                                       48
   37. Mandible                                                       48
   38. Hyoid                                                          49
   39. Skull, Dorsal Surface                                          50
   40. Skull, Side View                                               53
   41. Skull, Ventral Surface                                         55
   42. Cavities of Skull                                              57
   43. Skull, Median Section                                          60
   44. Scapula                                                        62
   45. Scapula                                                        62
   46. Clavicle                                                       64
   47. Humerus                                                        65
   48. Humerus                                                        65
   49. Radius and Ulna                                                68
   50. Radius and Ulna                                                68
   51. Bones of the Hand                                              70
   52. Ligaments of the Elbow                                         74
   53. Ligaments of the Elbow                                         74
   54. Innominate Bone of Kitten                                      76
   55. Innominate Bone                                                77
   56. Femur                                                          79
   57. Tibia and Fibula                                               81
   58. Bones of the Foot                                              83
   59. Calcaneus                                                      83
   60. Knee-joint                                                     89
   61. Knee-joint                                                     89
   62. Muscles of the Skin                                            94
   63. Muscles on Dorsal Side of Head                                 97
   64. Muscles of Face                                               102
   65. Ventral Muscles of Thorax, Neck, and Head                     109
   66. Pterygoid and Palatal Muscles                                 112
   67. Muscles of Tongue, Hyoid, and Pharynx                         114
   68. First Layer of Body Muscles                                   117
   69. Deep Muscles of the Vertebræ and Ribs                         125
   70. Dorsal Muscles of Lumbar and Caudal Regions                   127
   71. Deep Muscles of Neck                                          135
   72. Muscles on the Ventral Surface of the Cervical Vertebræ       143
   73. Second Layer of Body Muscles                                  149
   74. Diaphragm                                                     152
   75. Lateral Muscles of Arm                                        158
   76. Origin of Lateral Muscles on Scapula                          160
   77. Medial Muscles of Arm                                         162
   78. Origin of Medial Muscles on Scapula                           163
   79. Deep Medial Muscles of Arm                                    167
   80. Deep Lateral Muscles of Arm                                   169
   81. Areas of Origin of Muscles on Ventral Surface of Humerus      171
   82. Areas of Origin of Muscles on Medial Side of Humerus          171
   83. Areas of Origin of Muscles on Dorsal Surface of Left Humerus  171
   84. Tendons on Back of Hand                                       175
   85. Deep Muscles of Forearm                                       177
   86. Insertions of Muscles on Radius and Ulna                      178
   87. Insertions of Muscles on Radius and Ulna                      182
   88. Mm. Lumbricales, etc.                                         183
   89. Deep Muscles of Palm of Hand                                  184
   90. Lateral Muscles of the Leg                                    192
   91. Medial Muscles of the Leg                                     197
   92. Deep Medial Muscles of Thigh                                  200
   93. Teeth of the Upper Jaw                                        225
   94. Teeth of the Lower Jaw                                        226
   95. Tongue, Epiglottis, etc.                                      227
   96. Muscles of Tongue, Hyoid, and Pharynx                         229
   97. Stomach                                                       235
   98. Colon and Cæcum                                               238
   99. Ileocolic Valve                                               238
  100. Liver                                                         240
  101. Liver                                                         240
  102. Pancreas and Spleen                                           242
  103. Cartilages of Nose                                            244
  104. Cartilages of Larynx                                          247
  105. Muscles of Larynx                                             250
  106. Bronchi                                                       253
  107. Thymus Gland                                                  254
  108. Kidney                                                        255
  109. Section of Kidney                                             255
  110. Testis                                                        260
  111. Male Genital Organs                                           262
  112. Female Urogenital Organs                                      265
  113. Muscles of Urogenital Organs and Anus in Male                 270
  114. Muscles of Urogenital Organs of Female                        272
  115. Heart                                                         276
  116. Heart                                                         276
  117. Inside of Heart                                               278
  118. Vessels of Thorax                                             282
  119. Common Carotid and Internal Jugular                           284
  120. Branches of External Carotid                                  288
  121. Arteries of Brain                                             291
  122. Vessels and Nerves of the Axilla                              295
  123. Vessels and Nerves of the Arm                                 299
  124. Palmar Arch                                                   301
  125. Cœliac Artery                                                 302
  126. Abdominal Blood-vessels                                       305
  127. Medial Vessels and Nerves of the Leg                          310
  128. Deep Arteries of Foot                                         314
  129. Thoracic Blood-vessels                                        317
  130. Superficial Vessels and Nerves of the Forearm                 319
  131. Blood-vessels of the Face                                     322
  132. Portal Vein                                                   327
  133. Spinal Cord, cranial portion                                  336
  134. Section of Spinal Cord                                        337
  135. Origin of Spinal Nerves                                       337
  136. Cauda Equina, etc.                                            338
  137. Brain, Dorsal View                                            340
  138. Brain, Ventral View                                           342
  139. Diagram of Brain                                              343
  140. Diagram of Brain                                              343
  141. Dorsal View of Midbrain and ’Tween-brain                      350
  142. Ventral View of Midbrain and ’Tween-brain                     352
  143. Longitudinal Section of Brain                                 356
  144. Lateral View of Brain                                         358
  145. Diagram of Sulci and Gyri                                     359
  146. Diagram of Sulci and Gyri                                     361
  147. Corpus Callosum                                               363
  148. Fornix, Hippocampus, and Corpus Striatum                      364
  149. Transverse Section of Brain                                   366
  150. Transverse Section of Brain                                   366
  151. Transverse Section of Brain                                   366
  152. Transverse Section of Brain                                   367
  153. Transverse Section of Brain                                   367
  154. Cranial Nerves                                                374
  155. Nerves of Face                                                376
  156. Cranial Nerves in the Neck                                    379
  157. Sympathetic and Vagus in the Thorax                           381
  158. Nerves of the Neck                                            384
  159. Brachial Plexus                                               387
  160. Nerves and Vessels of Axilla                                  389
  161. Nerves and Vessels of Forearm                                 391
  162. Lumbar and Sacral Nerves                                      398
  163. Great Sciatic Nerve                                           401
  164. Sympathetic and Vagus in Abdomen                              407
  165. Nictitating Membrane                                          410
  166. Muscles of Eyeball                                            411
  167. Diagram of Eye                                                413
  168. Cartilage of External Ear                                     417
  169. Muscles of External Ear                                       419
  170. Tympanic Membrane                                             422
  171. Malleus and Incus                                             423
  172. Stapes                                                        424
  173. Membranous Labyrinth                                          425



ANATOMY OF THE CAT.



THE SKELETON OF THE CAT.


The skeleton of the cat consists of 230 to 247 bones exclusive of the
sesamoid bones (44) and the chevron bones (8). These are divided as
follows: head 35-40, vertebral column 52-53, ribs 26, sternum 1-8,
pelvis 2-8, upper extremities 62, lower extremities 54-56. The number of
bones varies with the age of the individual, being fewer in the old than
in the young animal, owing to the fact that in an old animal some bones
that were originally separate have united.


I. THE VERTEBRAL COLUMN. COLUMNA VERTEBRALIS.

The vertebral column, spinal column, or back-bone, consists of a varying
number of separate bones, the vertebræ. At its cranial end are seven
vertebræ (=cervical=, Fig. 1, _c_) which are without ribs and support
the head; caudad of these are thirteen rib-bearing vertebræ (=thoracic=,
Fig. 1, _m_); caudad of these are seven that are again without ribs
(=lumbar=, Fig. 1, _o_); these are followed by three vertebræ (=sacral=,
Fig. 1, _x_) which are united into a single bone, the =sacrum=, which
supports the pelvic arch. Following the sacral vertebræ are twenty-two
or twenty-three small ribless vertebræ which support the tail (=caudal=,
Fig. 1, _y_).

  [Illustration: FIG. 1.--SKELETON OF CAT.

  _a_, skull; _b_, hyoid; _c_, cervical vertebræ; _d_, clavicle; _e_,
  scapula; _f_, sternum; _g_, humerus; _h_, radius; _i_, ulna; _j_,
  carpus; _k_, metacarpus; _l_, phalanges; _m_, thoracic vertebræ; _n_,
  ribs; _o_, lumbar vertebræ; _p_, innominate bones; _q_, femur; _r_,
  patella; _s_, fibula; _t_, tibia; _u_, tarsus; _v_, metatarsus; _w_,
  phalanges; _x_, sacrum; _y_, caudal vertebræ.]


=Thoracic Vertebræ.= =Vertebræ thoracales= (Fig. 4).--The =thoracic
vertebræ= are most typical, and the fourth one of these may therefore be
first described (Figs. 2 and 3). It forms an oval ring which has
numerous processes and surrounds an opening which is the vertebral
foramen (_a_). The ventral one-third of this ring is much thickened and
forms the =centrum= or body (=corpus=) (_b_) of the vertebra. The
centrum is a semicylinder, the plane face of which bounds the vertebral
canal, while the curved surface is concave longitudinally and is
directed ventrad. The dorsal plane surface of the centrum is marked by
a median longitudinal ridge on either side of which is an opening
(nutrient foramen) for a blood-vessel. The ends are nearly plane, the
caudal being slightly concave; they are harder and smoother than the
other surfaces. They may be easily separated in a young specimen as thin
plates of bone known as =epiphyses=.

  [Illustration: FIG. 2.--FOURTH THORACIC VERTEBRA, CRANIAL END.

  FIG. 3.--FOURTH THORACIC VERTEBRA, SIDE VIEW.

  _a_, vertebral foramen; _b_, centrum; _c_, caudal, and _d_, cranial,
  costal demifacets; _e_, radix or pedicle; _f_, lamina; _g_, transverse
  process; _h_, cranial articular facet; _i_, caudal articular facet;
  _j_, caudal articular process; _k_, spinous process.]

At the caudal end of the centrum, at its dorsolateral angle, is a smooth
area on each side continuous with the surface of the epiphysis and
bounded dorsolaterally by a sharp ridge of bone (_c_). It is a =costal
demifacet=. In corresponding positions at the cranial end of the centrum
are two demifacets not limited by bony ridges (_d_). When the centra of
two contiguous thoracic vertebræ are placed together in the natural
position the cranial costal demifacets of one together with the caudal
demifacets of the other form two =costal= facets (Fig. 4, _e_), one on
each side, and each receives the head of a rib.

The dorsal two-thirds of the vertebral ring forms the =vertebral arch=
which is continued dorsally into the long, bluntly pointed =spinous
process= (Figs. 2 and 3, _k_) for attachment of muscles.

The vertebral arch (each half of which is sometimes called a
=neurapophysis=) rises on each side from the cranial two-thirds of the
dorsolateral angle of the centrum, as a thickened portion, the radix or
pedicle (Figs. 2 and 3, _e_), which forms the ventral half of the
lateral boundary of the vertebral canal. From the dorsal end of each
radix a flat plate of bone, the =lamina= (_f_), extends caudomediad to
join its fellow of the opposite side and form the vertebral arch. Owing
to the fact that the radix rises from only the cranial two-thirds of the
centrum there is left in the caudal border of the vertebral arch a notch
bounded by the radix, the lamina, and the centrum. There is also a
slight excavation of the cranial border of the radix. When the vertebræ
are articulated in the natural position, these notches form the
=intervertebral foramina= (Fig. 4, _d_), for the exit of the spinal
nerves.

At the junction of radix and lamina the arch is produced craniolaterad
into a short process, the =transverse process= (_g_), knobbed at the
end. On the ventral face of its free end the transverse process bears a
smooth facet, the transverse costal facet or tubercular facet (Fig. 4,
_c_), for articulation with the tubercle of a rib.

On the dorsal face of each lamina at its cranial border is a smooth oval
area, the =cranial articular facet= (superior articular facet of human
anatomy) (Figs. 2 and 3, _h_). Its long axis is oblique and it looks
dorsolaterad. The slight projections of the cranial edge of the laminæ
on which the facets are situated are the inconspicuous =cranial
articular processes= (prezygapophyses).

On the ventral surface of each lamina at the caudal border, near the
middle line is a similar area, the =caudal articular= =facet= (inferior
articular facet of human anatomy) (_i_); these occupy the ventral
surfaces of two projections which form the =caudal= (inferior)
=articular processes= (postzygapophyses) (_j_). These are separated by a
median notch. When the vertebræ are in their natural position the caudal
articular facets lie dorsad of the cranial facets and fit against them.
They thus strengthen the joint between contiguous vertebræ, while
permitting slight rotary motion.

  [Illustration: FIG. 4.--THORACIC VERTEBRÆ, SIDE VIEW.

  _a_, spinous processes; _b_, cranial articular processes; _c_,
  transverse costal facets; _d_, intervertebral foramina; _e_, costal
  facets; _f_, accessory processes; _g_, mammillary processes; _h_,
  caudal articular processes.]

=Differential Characters of the Thoracic Vertebræ= (Fig. 4).--Following
the thoracic vertebræ caudad there is to be seen a gradual increase in
the size of the centra brought about by an increase in their
craniocaudal and transverse measurements. The dorsoventral measurements
remain nearly the same. The costal facets (Fig. 4, _e_) shift caudad so
that on the eleventh, twelfth, and thirteenth thoracic vertebræ each
lies entirely on the cranial end of its centrum, while the caudal end of
the centrum immediately preceding is not marked by any part of it. In
the eleventh thoracic vertebra each costal facet is usually still
confluent with the smooth cranial end of the centrum. In the twelfth
vertebra the facets are separated by smooth ridges from the cranial end
of the vertebra, while in the thirteenth vertebra they are separated by
rough ridges.

The spinous processes (_a_) of the first four are of about the same
length. They then decrease in length to the twelfth, while the twelfth
and thirteenth are slightly longer than the eleventh. The first ten
slope more or less caudad, while the spinous process of the tenth
(=anticlinal=) vertebra is vertical and those of the eleventh, twelfth,
and thirteenth point craniad.

Each of the transverse processes of the seventh thoracic vertebra shows
a tendency to divide into three tubercles; one of these is directed
craniad, the mammillary process (or metapophysis), one caudad, the
accessory process (or anapophysis), while the third (transverse process
proper) looks ventrad and bears the transverse costal facet. This
division becomes more prominent in the succeeding vertebræ, being most
marked in the ninth and tenth. In the eleventh, twelfth, and thirteenth
vertebræ the mammillary (_g_) and accessory (_f_) processes are very
pronounced, while the transverse costal facet and that part of the
transverse process which bears it have disappeared. The ribs of the
eleventh, twelfth, and thirteenth vertebræ are thus attached to their
respective centra by their heads alone.

The cranial articular processes (_b_) are prominent on the first two
thoracic vertebræ; back of these they are very small as far as the
eleventh, so that the articular facets seem to be borne merely upon the
dorsal surface of the cranial edge of the laminæ. In the eleventh,
twelfth, and thirteenth the cranial articular processes are large,
bearing the articular facets on their medial surfaces, while the
mammillary processes appear as tubercles on the lateral surfaces of the
articular processes. The caudal articular processes (_h_) are prominent
in the first thoracic, then smaller until the tenth is reached; in the
tenth, eleventh, twelfth, and thirteenth they are large and their facets
are borne laterally, so as to face the corresponding cranial facets.
Thus from the tenth to the thirteenth thoracic vertebra rotary motion is
very limited, owing to the interlocking of the articular processes.


=The Lumbar Vertebræ.= =Vertebræ lumbales= (Fig. 5).--The last thoracic
vertebræ form the transition to the typical lumbar vertebræ. These are
larger than the thoracic vertebræ. The centra are of the form of the
centra of the thoracic vertebræ, and increase in length to the sixth,
but the seventh is about the length of the first. They increase in
breadth to the last.

  [Illustration: FIG. 5.--LUMBAR VERTEBRÆ.

  _a_, cranial articular processes; _b_, mammillary processes; _c_,
  caudal articular processes; _d_, accessory processes; _e_, transverse
  processes; _f_, spinous processes.]

The cranial articular processes (Fig. 5, _a_) are prominent and directed
craniodorsad; they have the facets on their medial surfaces, while
their dorsolateral surfaces bear the mammillary processes (_b_) as
prominent tubercles. The caudal articular processes (_c_) are likewise
large; their facets look laterad. When the vertebræ are articulated they
are received between the medially directed cranial processes.

The accessory processes (_d_) are well developed on the first vertebra,
diminish in size to the fifth or sixth, and are absent on the seventh
and sometimes on the sixth.

The transverse processes (more properly pseudo-transverse processes)
(_e_) arise from the lateral surface of the centra; are flat and are
directed ventrocraniolaterad. The first is small, and they increase in
length and breadth from the first to the sixth, those of the last being
slightly smaller than in the sixth. The free ends of the last four are
curved craniad.

The spinous processes (_f_) are flat and directed craniodorsad. They
increase in length to the fifth and then decrease. The first five are
knobbed at the end. In a dorsal view the spinous process and cranial
articular processes of each vertebra are seen to interlock with the
caudal articular processes and accessory processes of the preceding
vertebra in such a way as to prevent rotary motion, and this arrangement
may be traced craniad as far as the eleventh thoracic vertebra.


=Sacral Vertebræ.= =Vertebræ sacrales= (Figs. 6 and 7).--The three
sacral vertebræ are united in the adult into a single bone, the =os
sacrum=, or =sacrum=. In a kitten the three vertebræ are separate, while
in an animal almost mature the first two are united and the third is
still separate. The sacrum lies between the last lumbar and the first
caudal vertebræ and articulates laterally with the two innominate bones.
It is pyramidal, with the base of the pyramid directed craniad, and is
perforated by a depressed longitudinal canal, the =sacral canal=, which
is a continuation of the vertebral canal, and by four large foramina
dorsally and four ventrally. It may be described as having a cranial end
or base and a caudal end or apex, a dorsal, a ventral, and two lateral
surfaces.

The =base= is slightly oblique and presents a smooth transversely oval
articular facet (the cranial end of the centrum of the first sacral
vertebra), for articulation with the centrum of the last lumbar
vertebra. Dorsad of this is the sacral canal, more depressed than the
vertebral arch craniad of it. It supports a spinous process (Fig. 6,
_a_) which is directed dorsad. At the junction of its lamina and radix
is seen the prominent cranial articular process (_b_) with sometimes
slight indications of a mammillary process on its lateral surface.
Laterad of the articular facet is seen the cranial face of the expanded
“pseudo-transverse process” (_c_) of the first sacral vertebra. The
ventral border of the base is concave ventrad, forming an arc of about
120 degrees. The =apex= shows the caudal end of the last sacral centrum.
Dorsad of this are the vertebral arch with a very short spinous process
(_a′_), and the caudal articular processes (_d_). Laterad of the centrum
appears the laterally directed thin transverse process (_e_).

  [Illustration: FIG. 6.--SACRUM, DORSAL SURFACE.

  FIG. 7.--SACRUM, VENTRAL SURFACE.

  Fig. 6.--1, 2, 3, the three sacral vertebræ. _a_, _a′_, spinous
  processes; _b_, cranial articular process of first sacral vertebra;
  _c_, expanded transverse process of first sacral vertebra; _d_, caudal
  articular processes of third sacral vertebra; _e_, transverse
  processes of third sacral vertebra; _f_, tubercles formed by fused
  articular processes of the vertebræ; _g_, dorsal (or posterior) sacral
  foramina.

  Fig. 7.--1, 2, 3, the three sacral vertebræ. _a_, the transverse
  ridges formed by the union of the centra; _b_, cranial articular
  processes of first vertebra; _c_, transverse process of first
  vertebra; _d_, caudal articular processes of third vertebra; _e_,
  transverse processes of third sacral vertebra; _f_, _f′_, ventral (or
  anterior) sacral foramina; _g_, notch which helps to form third
  ventral sacral foramen.]

The ventral or pelvic surface (Fig. 7) is smooth, concave craniad,
convex caudad, and crossed by two transverse ridges (_a_) along which
are seen the ossified remains of the intervertebral fibro-cartilages. At
the ends of the first ridge is a pair of nearly circular =ventral= (or
anterior) =sacral foramina= (_f_) for the passage of sacral nerves. At
the end of the second ridge is a pair of ventral sacral foramina (_f′_),
smaller than the first pair and continued laterocaudad into shallow
grooves for the ventral rami of the sacral nerves. That portion of the
bone lying laterad of a line joining the medial borders of these two
pairs of foramina is known as the =lateral mass= of the sacrum and is
composed of the fused transverse processes of the sacral vertebræ. At
the caudal margin of the ventral surface there is a notch between the
lateral mass and the centrum (_g_). When the caudal vertebræ are
articulated, this notch helps to form a foramen for the third sacral
nerve.

The dorsal surface (Fig. 6) is narrower at its cranial end than is the
ventral surface. Its cranial border bears laterally a pair of cranial
articular processes (_b_) with their medially directed facets and
between them it is concave, so that a large dorsal opening is left into
the vertebral canal between the last lumbar vertebra and the sacrum.
Caudad of the articular processes are two pairs of tubercles (_f_).
These are the fused cranial and caudal articular processes of the sacral
vertebræ. Caudad of them are the caudal articular processes of the last
sacral vertebra (_d_). Craniolaterad of the middle and cranial tubercles
are =dorsal= (posterior) =sacral foramina= (_g_) for the transmission of
the dorsal rami of the sacral nerves. Three spinous processes (_a_)
appear between these rows of tubercles. They decrease in height caudad.
That part of the surface included between the spinous process and the
tubercles is made up of the fused laminæ of the sacral vertebræ. That
part between the tubercles and a line joining the lateral margins of the
dorsal (posterior) sacral foramina is formed by the fused radices of the
sacral vertebræ.

The lateral surface may be divided into two parts. Craniad is a large
rough triangular area with equal sides and with one of its angles
directed ventrocraniad. It is the lateral face of the pseudo-transverse
process of the first sacral vertebra (Fig. 6, _c_). A smooth curved
surface (the auricular facet) along its ventral edge articulates with
the ilium, while the dorsal portion is rough for attachment of
ligaments. Caudad is the narrow longitudinal triangular area of the
lateral faces of the fused transverse processes of the second and third
sacral vertebræ.


=Caudal Vertebræ.= =Vertebræ caudales= (Fig. 1, _y_, and Figs. 8 and
9).--The caudal vertebræ (21-23 in number) decrease gradually in size to
the last one. Caudad they become longer and more slender and lose the
character of vertebræ. They become finally reduced to mere
centra,--slender rods of bone knobbed or enlarged at their two ends
(Fig. 8). The last one is more pointed than the others and bears at its
caudal end a small separate conical piece, the rudiment of an additional
vertebra.

  [Illustration: FIG. 8.

  FIG. 9.

  Fig. 8.--Caudal Vertebra, from near the caudal end of the tail.

  Fig. 9.--Fourth Caudal Vertebra, ventral view. _a_, transverse
  processes; _b_, cranial articular processes; _c_, hæmal processes;
  _d_, chevron bone.]

The parts of a typical vertebra--vertebral arch, transverse processes,
cranial and caudal articular processes--may be recognized in the
vertebræ as far back as the eighth or ninth. The transverse processes
(Fig. 9, _a_) are directed caudad and decrease rapidly in length. They
are very small on the ninth vertebra, but may be recognized for a
considerable distance back of this. The spinous process disappears at
about the fourth caudal vertebra, and the vertebral canal becomes
gradually smaller caudad, until on the eighth or ninth vertebra it
becomes merely a groove open dorsad.

Caudad of the third vertebra for a considerable distance, each centrum
bears on each lateral face at its cranial end a short =anterior
transverse= process, and on its ventral face at its cranial end a pair
of rounded tubercles, =hæmal processes= (_c_), which articulate with a
small pyramidal =chevron= bone (_d_) so as to enclose a canal. These
structures disappear caudad.


=Cervical Vertebræ.= =Vertebræ cervicales= (Fig. 10).--The cervical
vertebræ number seven. The first two of these are so peculiar as to
require a separate description, so that the last five may be first
considered.

Passing craniad from the fourth thoracic vertebra to the third cervical
there is a gradual transition. The centra of the cervical vertebræ are
broader and thinner than those of the thoracic vertebræ, while the
vertebral arches and vertebral canal are larger (Fig. 11). The caudal
end of each centrum is concave and looks dorsocaudad when the centrum is
held with its long axis horizontal. The cranial end of the centrum is
convex and looks ventrocraniad when the centrum is horizontal. These
peculiarities are more marked in the third vertebra than in the seventh.
The spinous processes grow rapidly shorter as we pass craniad; the
fifth, sixth, and seventh are directed dorsocraniad, the third and
fourth dorsad.

  [Illustration: FIG. 10.--CERVICAL VERTEBRÆ, SIDE VIEW.

  _a_, spinous processes; _b_, cranial articular processes; _c_, caudal
  articular facet; _d_, intervertebral foramina; _e_, transverse process
  proper; _f_, processus costarius; _g_, wing of the atlas; _h_, dorsal
  arch of the atlas; _i_, atlantal foramen.]

The caudal articular processes are situated at the junction of the
radices and laminæ; their facets (Fig. 10, _c_) look ventrocaudolaterad.
The cranial articular processes also become more prominent than is the
rule in the thoracic vertebræ; they are borne at the junction of radix
and lamina and have their facets (Fig. 11, _b_) directed dorsomediad.
The cranial and caudal articular processes of each side are joined by a
prominent ridge which is most pronounced in the third, fourth, and fifth
vertebræ.

The characteristic feature of the cervical vertebræ is their transverse
process, so called. In each of them it arises by two roots, one from the
centrum and one from the arch. These two roots, which are broad and
thin, converge and unite so as to enclose a canal or foramen, the
=foramen transversarium= (Fig. 11, _g_), for the vertebral artery.
Laterad of the foramen the two parts of the process are, in the third
cervical, almost completely united, the dorsal part being, however,
distinguishable as a tubercle at the caudolateral angle of the thin
plate formed by the process as a whole. This dorsal component is the
=transverse process proper= (Figs. 10 and 11, _e_), while the ventral
portion represents a rib, and is hence known as the =processus
costarius= (_f_). The expanded plate formed by the union of these two
processes is directed nearly ventrad and somewhat craniad in the third,
fourth, and fifth vertebræ. The two components of the process gradually
separate as we pass caudad; in the fourth and fifth vertebræ the part
which represents the transverse process proper forms a very prominent
tubercle at the caudolateral angle of the plate formed by the processus
costarius. In the sixth (Fig. 11) the two parts are almost completely
separated; the dorsal part forms (_e_) a slender knobbed process, while
the processus costarius is divided into two portions (_f_ and _f′_) by a
broad lateral notch. In the seventh the ventral part (processus
costarius) is usually quite lacking, though sometimes represented by a
slender spicule of bone. In the former case the foramen transversarium
is of course likewise lacking.

  [Illustration: FIG. 11.--SIXTH CERVICAL VERTEBRA, CRANIAL END.

  FIG. 12.--ATLAS, VENTRAL VIEW.

  Fig. 11.--_a_, spinous process; _b_, cranial articular facet; _c_,
  lamina; _d_, radix or pedicle; _e_, transverse process proper; _f_,
  _f′_, processus costarius; _g_, foramen transversarium; _h_, centrum;
  _i_, vertebral canal.

  Fig. 12.--_a_, ventral arch; _b_, tuberculum anterius; _c_, lateral
  masses; _d_, transverse processes; _e_, cranial articular facets; _f_,
  groove connecting the foramen transversarium with the atlantal
  foramen; _g_, atlantal foramen; _h_, caudal articular facets.]

=The Atlas= (Fig. 10, 1; Fig. 12).--The first cervical vertebra or atlas
has somewhat the form of a seal ring. The centrum is absent; it has
united with the second vertebra to form the odontoid process or dens.
Its place is taken in the atlas by a narrow flat arch of bone, narrower
at the ends than in the middle, the =ventral arch= (Fig. 12, _a_) of the
atlas. This connects the lateral, thicker portions of the ring ventrally
and bears on its caudal margin a blunt tubercle (=tuberculum anterius=,
Fig. 12, _b_). Laterally the ring is thickened, forming thus the
=lateral masses= (_c_) which are continued into the broad thin
transverse processes (Fig. 10, _g_; Fig. 12, _d_). Each lateral mass
bears at its cranial end on its medial surface a concave, pear-shaped
facet, cranial (or superior) articular facet, (Fig. 12, _e_) for
articulation with the condyles of the skull. These facets look
craniomediad. Dorsad of each is a foramen, the atlantal foramen (Fig.
10, _i_; Fig. 12, _g_), which pierces the dorsal arch at its junction
with the lateral mass. Caudal to the facet, on the medial face of each
lateral mass, within the vertebral canal, is a tubercle. To the two
tubercles are attached the transverse ligament (Fig. 14, _b_) which
holds in place the odontoid process (dens) of the axis.

That part of the lateral mass which bears the articular facet projects
craniad of the dorsal arch and is separated by a deep triangular notch
from the transverse process. Along the bottom of this notch runs a
groove (Fig. 12, _f_), convex craniad, which connects the cranial end of
the foramen transversarium and the atlantal foramen. The vertebral
artery passes along it. The foramen transversarium is circular. It is
bounded laterally by the lateral masses, and dorsally by the dorsal
arch.

The dorsal arch (Fig. 10, _h_) is two to three times as broad as the
ventral, has a thick convex cranial border with a median notch, and a
thin concave caudal border.

  [Illustration: FIG. 13.--AXIS OR EPISTROPHEUS, SIDE VIEW.

  _a_, odontoid process or dens; _b_, cranial articular facets; _c_,
  spinous process; _d_, caudal articular facet; _e_, transverse process;
  _f_, foramen transversarium.]

The caudal articular facets (Fig. 12, _h_) are borne by the caudal ends
of the lateral masses. They are slightly concave, triangular, and look
caudomediad, so that their dorsal borders form with the caudal border of
the dorsal arch nearly a semicircle. The transverse processes are flat
and directed laterad. The attached margin of each is about two-thirds
the length of the thinner free margin. The somewhat thicker caudal end
of the transverse process projects further caudad than any other part of
the vertebra and is separated by a slight notch from the caudal
articular facet. From the bottom of this notch the foramen
transversarium extends craniad and opens at the middle of the ventral
face of the transverse process.

=Epistropheus= or =Axis= (Fig. 10, 2; Fig. 13).--The second cervical
vertebra (epistropheus or axis) is not so wide as the atlas but is much
longer. Craniad the centrum is continued into a slender conical,
toothlike projection, the =dens= or =odontoid process= (Fig. 13, _a_)
which represents the centrum of the atlas. The dens is smooth below for
articulation with the ventral arch of the atlas. It is rougher above.
Laterad of the dens the centrum bears a pair of large cranial articular
facets (_b_) which look craniolaterad. These have each the form of a
right-angled triangle with rounded angles, one side of the triangle
being nearly horizontal. Each is separated from the articular face of
the dens by a roughened groove. The spinous process (_c_) runs the
length of the vertebral arch. It extends craniad of the vertebral arch
nearly as far as the dens, as a flat rounded projection. Caudad of the
vertebral arch it projects for a short distance as a stout triangular
spine. The caudal articular facets (_d_) are borne on thickenings of the
caudolateral portions of the arch; they face almost directly ventrad.
The transverse process (_e_) is slender and triangular and directed
nearly caudad. Its apex reaches no farther than the caudal or articular
face of the centrum. Its base is traversed by the foramen transversarium
(_f_).

=Differential Characters of the Cervical Vertebræ.=--It is possible to
identify each of the cervical vertebræ:

The first by the absence of the centrum.

The second by the dens or odontoid process.

The third by the small spinous process and slightly marked tubercle of
the transverse process, and by a median tubercle on the cranial border
of the vertebral arch.

The fourth by the spinous process directed dorsad, and the short thick
tubercle of the transverse process not trifid.

The fifth by the spinous process directed craniad, and the more slender
spine-like tubercle of the transverse process not trifid.

The sixth by the trifid transverse process.

The seventh by the long spinous process and the slender simple
transverse process, and by the usual absence of the foramen
transversarium.


LIGAMENTS OF THE VERTEBRAL COLUMN.

=Fibro-cartilagines intervertebrales.=--The separate vertebræ (except
the atlas and axis) are united by the disk-shaped =intervertebral
fibro-cartilages=, which are situated between the centra of the
vertebræ. Each consists of a central pulpy portion and a fibrous outer
portion, covered by strong intercrossing tendinous fibers which unite
with the periosteum of the vertebræ.

=Ligamentum longitudinale anterius.=--On the ventral face of the centra
of the vertebræ, from the atlas to the sacrum, lies a longitudinal
ligament, the =anterior longitudinal ligament=. It is very small, almost
rudimentary, in the cervical region: large and strong in the thoracic
and lumbar regions.

=Ligamentum longitudinale posterius= (Fig. 14, _a_).--A corresponding
ligament (=posterior longitudinal ligament=) lies on the dorsal surface
of the centra (therefore within the vertebral canal). It is enlarged
between each pair of vertebræ and closely united to the intervertebral
fibro-cartilages.

=Ligamentum supraspinale.=--Between the tips of the spinous processes of
the thoracic and lumbar vertebræ extend ligamentous fibers. They are not
united to form a distinct band, and can hardly be distinguished from the
numerous tendinous fibers of the supraspinous muscles. Together they
represent the =supraspinous ligament=. From the tip of the spinous
process of the first thoracic vertebra to the caudal end of the spine of
the axis extends a slender strand representing the =ligamentum nuchæ= or
=cervical supraspinous ligament=. It is imbedded in the superficial
muscles of this region, some of which take origin from it.

Ligamentous fibers are also present between the spinous processes of the
vertebræ (=ligamenta interspinalia=): between the transverse processes
(=ligamenta intertransversaria=), and between the vertebral arches
(=ligamenta flava=).

=Capsulæ articulares.=--The joints between the articular processes are
furnished with =articular capsules= attached about the edges of the
articular surfaces. These are larger and looser in the cervical region.

=Atlanto-occipital Articulation.=--The joint between the atlas and the
occipital condyles has a single articular capsule, which is attached
about the borders of the articular surfaces of the two bones. This
capsule is of course widest laterally, forming indeed two partially
separated sacs, which are, however, continuous by a narrow portion
across the ventral middle line. This capsule communicates with that
which covers the articular surface of the dens, and through this with
the capsule between the atlas and axis. That portion of the capsule
which covers the space between the ventral arch of the atlas and the
occipital bone represents the =anterior atlanto-occipital membrane=; it
is strengthened by a slender median ligamentous strand. The =posterior
atlanto-occipital= membrane covers in the same way the space between the
dorsal arch of the atlas and the dorsal edge of the foramen magnum. In
it a number of different sets of fibers, with regard to direction and to
degree of development, may be distinguished; these have sometimes been
considered separate ligaments.

The =lateral ligaments= of the atlas begin at the lateral angle of the
cranial margin of the atlas, at about the junction of its dorsal and
ventral arches, and pass cranioventrad to the jugular processes.

=Articulation between the Axis and Atlas.=--The =articular capsule= is
large and loose, being attached to dorsal and ventral borders of the
atlas, about the articular surfaces of the axis, and to the cranial
projection of the spine of the atlas. It also passes craniad along the
ventral side of the dens and communicates here with the capsule of the
atlanto-occipital articulation. In the dorsal part of the capsule a
short strong ligamentous strand is developed, connecting the caudal
border of the dorsal arch of the atlas with the tip of the cranial
projection of the spinous process of the axis.

  [Illustration: FIG. 14.--LIGAMENTS OF THE ODONTOID PROCESS OR DENS.

  First three cervical vertebræ and base of the skull, with dorsal
  surface removed. _a_, ligamentum longitudinale posterius; _b_,
  transverse ligament of the atlas; _c_, ligamenta alaria; _d_, odontoid
  process; _e_, occipital condyles; 1, 2, 3, the first three cervical
  vertebræ; 4, basal portion of the occipital bone.]

The dens or odontoid process is held in place by the =transverse
ligament= (Fig. 14, _b_) of the atlas, which passes across the process
as it lies within the vertebral canal of the atlas. The transverse
ligament is attached at its two ends to the medial surface of the sides
of the atlas at about the region where the dorsal and ventral arches of
the atlas unite.

From the cranial end of the odontoid process the two =ligamenta alaria=
(Fig. 14, _c_) diverge craniolaterad to the rough ventromedial angle of
the condyles of the occipital bone.


=II. RIBS. COSTÆ= (Figs. 1 and 15.)

The cat has thirteen pairs of ribs. One of the fifth pair (Fig. 15) may
be taken as typical. It is a curved flattened rod of bone attached at
its dorsal end to the vertebral column, and at its ventral end to a
cartilage (=costal cartilage=, Fig. 15, _f_) which serves to unite it to
the sternum.

The most convex portion of the bone is known as the =angle= (_e_). Each
rib presents a convex lateral and a concave medial surface, a cranial
and a caudal border. The borders are broad dorsad and narrow ventrad,
while the surfaces are narrow dorsad and broad ventrad. The rib has thus
the appearance of having been twisted.

The rib ends dorsad in a globular head or =capitulum= (_a_), by which it
articulates with the costal demifacets of two contiguous thoracic
vertebræ. Between the capitulum and angle on the lateral surface is an
elevated area, the =tubercle=, marked by the smooth tubercular facet
(_c_) for articulation with the transverse process of a vertebra. The
constricted portion between the head and tubercle is known as the =neck=
(=collum=) (_d_). The angle is marked by a projecting process (_e_)
(=angular process=) on its lateral border, for attachment of a ligament.

  [Illustration: FIG. 15.--FIFTH RIB OF LEFT SIDE, CRANIAL VIEW.

  _a_, head; _b_, tubercle; _c_, tubercular facet; _d_, neck; _e_,
  angle, with angular process; _f_, cartilage.]

The ribs increase in length to the ninth (the ninth and tenth are of the
same length) and then decrease to the last. They decrease in breadth
behind the fifth. The first is nearly in a dorsoventral plane, while the
others have their dorsal ends inclined slightly craniad.

  [Illustration: FIG. 16.--STERNUM, VENTRAL VIEW.

  _a_, manubrium; _b_, the separate pieces forming the body; _c_, bony
  part of the xiphoid process (the expanded cartilaginous portion not
  being shown); _d_, facet for attachment of first rib.]

The tubercles become less prominent as we pass caudad and are absent on
the last two or three ribs, which do not articulate with the transverse
process.

The first nine ribs (=true ribs= or =costæ veræ=) are attached
separately to the sternum by their costal cartilages. The last four
(false ribs or costæ spuriæ) are not attached separately to the sternum.
The costal cartilages of the tenth, eleventh, and twelfth are united to
one another at their sternal ends. They may be united also to the ninth
costal cartilage or to the sternum by a common cartilage of insertion,
or they may be quite free from the sternum. The thirteenth costal
cartilages are free (floating ribs).

=Ligaments of the Ribs.=--The articular surfaces between the head of the
rib and the centra, and between the tubercle and the transverse process
of the vertebra, have each an articular capsule. There are also a number
of small ligamentous bands from the tuberosity and the neck of the rib
to the transverse process of the vertebra.


=III. STERNUM.= (Fig. 16.)

The sternum consists of three portions, a cranial piece or =manubrium=
(_a_), a caudal piece or =xiphoid= process (_c_), and a middle portion
or =body= (=corpus=), which is divided into a number of segments (_b_).

To the sternum are united the ventral ends of the first nine ribs. It
thus forms the median ventral boundary of the thorax. Since the thorax
decreases in dorsoventral measurement craniad, the long axis of the
sternum is inclined from its caudal end dorsocraniad, and if continued
would strike the vertebral column in the region of the first cervical
vertebra.

The manubrium (_a_) makes up about one-fifth the whole length of the
sternum and projects craniad of the first rib. It has the form of a
dagger and presents a dorsal surface and two lateral surfaces, the
latter uniting ventrad to form a sharp angle. In the middle of the
lateral surface near the dorsal margin is an oval articular surface
(_d_) borne on a triangular projection. It looks caudodorsad and is for
the first costal cartilage.

The caudal end articulates with the body by a synchondrosis and presents
a slightly marked oval facet on each side for the second costal
cartilage.

The body consists of six cylindrical pieces (_b_) enlarged at their ends
and movably united by synchondroses. They increase in breadth from the
first, and decrease slightly in length and thickness. At the caudal end
of each near its ventral border there is a pair of facets looking
caudolaterad. They are for the costal cartilages.

The xiphoid process (_c_) is a broad thin plate of cartilage at its
caudal end; bony and cylindrical at its cranial end. It is attached by
its base to the last segment of the body by a considerable cartilaginous
interval, while the opposite end is free and directed caudoventrad.

The cartilage of the ninth rib is attached to the lateral face of the
cartilage between the xiphoid and the body, and just caudad of this the
common cartilage of insertion of the tenth, eleventh, and twelfth costal
cartilages is attached, if present.


IV. THE SKULL.

The bones of the head consist of the =skull proper= together with a
number of separate bones forming part of the =visceral skeleton=; these
are the lower jaw, the hyoid, and the ear-bones.

The skull proper is considered as divided into =cranial= and =facial=
portions. The former includes all the bones which take part in bounding
the cranial cavity or cavity of the brain; the latter includes the bones
which support the face.

The cranial portion of the skull includes all that part enclosing the
large cavity which contains the brain. For convenience this portion may
be considered as made up of three segments, each of which forms a ring
surrounding a part of the cranial cavity. The first or caudal segment or
ring consists of the occipital bone (with the interparietal) surrounding
the foramen magnum. The second segment consists of the sphenoid ventrad,
the parietals laterad and dorsad. Between the first and second segments
are intercalated laterally the temporal bones containing the auditory
organ. The third segment or ring consists of the presphenoid ventrad, of
the frontals laterad and dorsad. The cranial opening of this ring is
closed by the lamina cribrosa of the ethmoid.

The cranial portion of the skull therefore contains eleven separate
bones: one occipital, one interparietal, two temporals, one sphenoid,
two parietals, one presphenoid, two frontals, and one ethmoid.

The facial portion of the skull is much smaller than the cranial, and
lies craniad of the latter; it encloses the nasal cavity. It contains
the following thirteen bones: two palatines, one vomer, two maxillaries,
two lachrymals, two premaxillaries, two nasals, two malar or zygomatic
bones. The two halves of the mandible or lower jaw are frequently
included in the facial portion of the skull, making in all fifteen
separate bones in this part of the skull.

In the following the bones of the skull are first described separately,
then an account is given of the skull as a whole.


=Occipital Bone.= =Os occipitale= (Figs. 17 and 18).--The occipital bone
forms the most caudal portion of the cranium, entering into the
formation of its caudal wall and of its base. It connects the cranium
with the vertebral column and surrounds a large opening, the =foramen
magnum= (_d_), by means of which the cranial cavity communicates with
the vertebral canal.

  [Illustration: FIG. 17.--OCCIPITAL BONE, CAUDAL OR OUTER SURFACE.

  FIG. 18.--OCCIPITAL BONE, INNER SURFACE.

  _a_, basilar portion; _b_, lateral portions; _c_, squamous portion;
  _d_, foramen magnum; _e_, occipital condyles; _f_, jugular processes;
  _g_, jugular notch; _h_, lambdoidal ridge; _i_, external occipital
  crest; _j_, external occipital protuberance.]

In young kittens four portions may be distinguished in this bone. These
are, a basal portion (the =basioccipital bone=), two lateral portions
(the =exoccipital bones=), and a dorsal portion (the =supraoccipital
bone=). These four bones remain separate through life in many lower
vertebrates. In the adult cat they are completely united into a single
bone, but it is convenient to describe this bone as made up of four
parts: a basal portion (_a_) (=pars basilare=), corresponding to the
basioccipital, two lateral portions (_b_) (=partes laterales=),
corresponding to the exoccipitals, and a squamous portion (_c_) (=squama
occipitalis=) corresponding to the supraoccipital.

The basilar portion (_a_) as seen from the dorsal or ventral surface is
oblong and flattened. It is broadest at the junction of its middle and
last thirds, and tapers toward both ends. It presents a cranial end and
a caudal end, a dorsal, a ventral, and two lateral surfaces. Its caudal
end, which helps to form the ventral boundary of the foramen magnum, is
concave from side to side. The cranial end is transversely elongate,
about five times as broad as high, pointed laterally and roughened for
attachment to the caudal end of the body of the sphenoid, which has a
corresponding form. The joint is a synchondrosis.

The dorsal surface is concave from side to side, forming a longitudinal
groove in which rest the pons and medulla. The concavity is more
pronounced caudad, where the bone is thinner at its middle.

The ventral surface is marked by three parallel longitudinal ridges. One
of them is median and expands caudad into a smooth triangular elevated
area which extends to the foramen magnum. The other two ridges run near
the lateral edges of the bone. Between them and the median ridge the
surface is smooth and is depressed caudad. Laterad of each lateral ridge
is a rough triangular surface overlaid in the natural state by the
medial edge of the tympanic bulla.

The lateral surfaces are smooth and sharp and abut against the petrous
portion of the temporal bone. They pass into the lateral portions of the
occipital caudad.

The =lateral portions= (_b_) of the occipital arise from the caudal
margin of the basilar portion in the transverse plane; a short distance
laterad of the line of junction they turn dorsad at an angle of nearly
ninety degrees. They form the lateral boundaries of the foramen magnum
and pass dorsally into the squamous portion.

The external surface of each presents an elongated elevated spirally
curved surface, the =occipital condyle= (_c_), for articulation with the
atlas. A small part of each condyle is formed from the basal portion.
The two condyles are separated from one another ventrally by a narrow
notch, and each extends (laterad) along the border of the foramen magnum
to a point slightly dorsad of the transverse diameter of the latter.

Laterad of each condyle the bone is elevated into a blunt triangular
projection, the =jugular process= (_f_), which covers the caudal end of
the tympanic bulla. Between the jugular process and the condyle is a
deep depression.

The internal surface (Fig. 18) is concave dorsoventrally, following the
outline of the foramen magnum. It is convex from side to side. It is
smooth except at its outer margin, which is rough for articulation with
the mastoid portion of the temporal bone. The cranial face of the
jugular process (_f_) shows a rough concavity for the reception of the
bulla tympani. Mediad of the jugular process is a notch (=jugular
notch=) (_g_) which when the bones are articulated forms part of the
boundary of the jugular foramen. Mediad of this notch is a foramen which
forms one end of the =hypoglossal canal=. It passes dorsocaudad into the
cranial cavity and transmits the hypoglossal nerve. Dorsad of the
hypoglossal canal is the cranial opening of the =condyloid canal=, which
passes caudad and opens just craniad of the dorsal end of the condyle.
It transmits a vein. The outer border of this portion is rough for
articulation with the petrous and mastoid portions of the temporal.

The =squamous portion= (_c_) has the form of a sector of a circle whose
arc is a little more than ninety degrees. The central angle of the
sector is truncated and bounds the foramen magnum dorsally. The arc of
the sector forms the dorsal margin of the bone, while along the radii it
passes into the lateral portions. Its dorsal portion is thick and
porous; its ventral portion near the foramen magnum is thin and compact.

The external surface (Fig. 17) is marked by a prominent ridge, the
=lambdoidal ridge= (_h_), parallel with the dorsal border and near to
it. The narrow portion of the outer surface that lies dorsad of the
ridge forms an angle of about ninety degrees with the remainder of the
surface.

A median crest (_i_) extends ventrad from the middle of the lambdoidal
ridge toward the foramen magnum; this is the =external occipital crest=.
At its junction with the lambdoidal ridge it is elevated into a
tubercle, the =external occipital protuberance= (_j_).

The inner surface (Fig. 18) presents depressions for the convolutions of
the cerebellum.

The dorsal border is thick and rough for articulation with the parietals
and interparietal. The ventral border abuts on the foramen magnum and is
thin and smooth.


=Interparietal Bone.= =Os interparietale= (Fig. 19).--This is a small
triangular bone lying between the parietals, with its apex directed
craniad, and its base in contact with the squamous portion of the
occipital.

Its dorsal surface is arrow-shaped and has its posterior border notched.
It is marked by a median crest (part of the =sagittal crest=) which is
continued craniad from the middle of the lambdoidal crest.

The ventral surface is irregularly triangular, smooth, and concave. The
three borders are rough for articulation with the parietals and
occipital.

  [Illustration: FIG. 19.--INTERPARIETAL BONE, OUTER SURFACE.

  FIG. 20.--SPHENOID BONE, DORSAL OR INTERNAL SURFACE.

  Fig. 19, showing the sagittal crest running craniocaudad across its
  middle.

  Fig. 20.--_a_, body; _b_, wings; _c_, pterygoid process; _d_,
  tuberculum sellæ; _e_, dorsum sellæ; _f_, sella turcica; _g_, notch
  which aids in forming the foramen lacerum; _h_, longitudinal groove of
  alisphenoid; _i_, notch which aids in forming the orbital fissure;
  _j_, foramen rotundum; _k_, foramen ovale.]


=Sphenoid Bone.= =Os sphenoidale= (Fig. 20).--The sphenoid bone of man
is represented in the cat by two entirely distinct bones,--one cranial,
the other caudal. The cranial portion may be designated as the
=presphenoid= (Fig. 21); the caudal part will be described as the
=sphenoid= (proper) (Fig. 20).

The sphenoid bone in the kitten is in three parts: a central portion,
the =basisphenoid=, and two lateral portions, the =alisphenoids=. In
many lower vertebrates these three bones are permanently distinct, but
in the adult cat they are united to form the sphenoid bone. To these
there is added a fourth element, separate in many vertebrates as the
=pterygoid= bone. The sphenoid may thus be described as composed of a
central portion, the body (_a_) (basisphenoid), and of two thin expanded
wings (_b_) (alisphenoids, alæ magnæ of the human sphenoid); each of
which has arising from it a thin curved process, the =pterygoid process=
(_c_), directed craniad and largely made up of the pterygoid bone.

The body of the sphenoid (_a_) lies in the middle line of the base of
the skull. It is wedge-shaped, with the converging sides of the wedge
directed laterad and its apex pointed craniad.

It has six surfaces, of which the dorsal and a part of the laterals look
into the cranial cavity. The cranial end articulates with the body of
the presphenoid, and the caudal with the body of the occipital.

The dorsal surface is triangular, with one apex of the triangle
truncated, elevated, and directed craniad. This elevation is the
=tuberculum sellæ= (_d_). Just caudad of the middle the surface presents
a rectangular elevation with rounded angles, the =dorsum sellæ= (_e_).
The cranial end of the dorsum sellæ presents at each dorsolateral angle
a very small smooth tubercle which represents one of the posterior
clinoid processes of man. Between this elevation and the elevated
cranial end of this surface there is a deep excavation, the =sella
turcica= (_f_), in which in the natural state is lodged the hypophysis.
Near the cranial end of the sella is a small foramen, probably nutrient.
At the caudal end of the body a slight notch (_g_) separates it from the
wing: this notch forms a part of the =foramen lacerum=. Against this
notch fits the apex of the petrous bone, and from it a groove (=carotid
groove=) is continued mediocraniad to the sella turcica.

The ventral surface (Fig. 41, 3) is triangular, smooth, and nearly flat;
it is marked by a median ridge which is the continuation craniad of the
ridge on the ventral face of the basilar portion of the occipital.

Its caudal angles are separated from the rest of the bone by sharp
triangular elevations, laterad of which are rough triangular areas,
overlaid when the bones are articulated by a triangular spine from the
tympanic bulla.

Its lateral surfaces are mostly covered by the wings. They appear at the
sides of the elevated cranial end of the dorsal surface as triangular
areas.

The caudal end is concave, rough, and has the form of the cranial end of
the basilar part of the occipital.

The cranial end is nearly square and rough for articulation with the
body of the presphenoid.

=The Wing= (=alisphenoid=; ala magna of the human sphenoid) (Fig. 20,
_b_).--This is a thin quadrilateral plate of bone attached by its medial
border to nearly the whole of the lateral surface of the body. Its
middle portion lies nearly in the same plane as the body, but its ends
are curved dorsad so that its internal surface is concave and its
external surface is convex. The curvature is most pronounced near the
long lateral border, so that this border forms nearly a semicircle.

The internal surface supports the occipital lobe of the cerebrum. It is
marked by a rounded groove (=h=) which is parallel with the lateral
surface of the body. The dorsal margin of the groove projects mediad in
the form of a sharp ridge which is broadest caudad, where it often
reaches nearly to the posterior clinoid process. The groove passes
craniad into three foramina. The first (cranial) of these, the =orbital
fissure= (_i_), is large and lies between the wing, the body, and the
pterygoid process. It is incomplete, but is completed by the
presphenoid. The second foramen is small and rounded; it is the =foramen
rotundum= (_j_). The third, =foramen ovale= (_k_), is larger and oval
and penetrates the wing through about the middle of its longitudinal
axis. Another minute foramen penetrates the sphenoid between the wing
and the body of the bone, just laterad of the tuberculum sellæ. This
foramen is continuous craniad with a groove on the dorsal surface of the
pterygoid process; the groove and foramen constitute the =pterygoid
canal=. It transmits a nerve.

The external surface shows the orbital fissure, the foramen rotundum and
the foramen ovale, bounded ventrally by a sharp ridge, which is
continued onto the pterygoid process. Between this ridge and the body
the surface is longitudinally grooved for the tuba auditiva or
Eustachian tube.

The semicircular margin of the bone articulates with the squamous
portion of the temporal. At the junction of its caudal and middle third
there is sometimes a toothlike projection which underlies the root of
the zygoma.

The whole of the cranial margin, except the lateral end, articulates
with the wing of the presphenoid. At this end the angle formed by the
junction of lateral and cranial borders is produced into a flat process,
which passes dorsocaudad between the squamous portion of the temporal
and the frontal, and articulates by the roughened internal surface of
its free end with a similar process from the parietal.

The caudal margin laterad of the groove is bevelled and roughened at the
expense of the dorsal surface and is overlaid by the ventral end of the
tentorium. Mediad of the groove it projects caudad as a slender point,
the =lingula= of the sphenoid. This is received into a narrow cleft
between the apex of the petrous bone and the bulla tympani.

The pterygoid process (_c_) is a nearly square, thin plate of bone. The
medial surface is smooth and concave, the lateral face is convex and
marked by two parallel ridges. The medial one of these is continued
craniad from the bony septum which separates the orbital fissure from
the foramen rotundum, and the lateral one from the septum which
separates the foramen rotundum from the foramen ovale. A sharp
triangular spine projects laterad from near the caudal end of the
lateral ridge.

The two ridges and that part of the lateral surface of the bone included
between them form a part of the sphenoid bone known as the pterygoid
process of the sphenoid bone, in those cases where the pterygoid is a
separate bone.

The remainder of the process is equivalent to the pterygoid bone of
other vertebrates.

Between the caudal margin of this bone and the lateral of the two
ridges, i.e., between the pterygoid bone and the pterygoid process of
the sphenoid, is a long deep fossa, the =internal pterygoid fossa= (Fig.
40, _s_). The laterocaudal margin of the pterygoid process projects
caudad, as a curved triangular spine, the =hamulus= or =hamular process=
(Fig. 40, _t_; Fig. 43, _i_).


The =Presphenoid Bone=. =Os presphenoidale= (Fig. 21).--In a young cat
this bone is in three pieces, a basal portion (=presphenoid=) and two
wings (=orbitosphenoid bones=). These bones remain distinct throughout
life in many lower vertebrates, but in the adult cat they fuse to form a
single bone. We may nevertheless conveniently describe this bone as made
up of a body (_a_) (the basisphenoid), and two wings (_b_), the
orbitosphenoids (the alæ parvæ of the human sphenoid).

  [Illustration: FIG. 21.--PRESPHENOID BONE, VENTRAL VIEW.

  _a_, body; _b_, wings; _c_, optic foramina.]

The body (_a_) lies in the base of the skull in the median line, craniad
of the basisphenoid. It has the form of a rectangular prism about twice
as long as broad. It is hollow, and the cavity is divided by a median
longitudinal partition into two cavities (=sphenoidal sinuses=, Fig. 43,
_l_). The sphenoidal sinuses are continued craniad into the cavities of
the ethmoid. The body has six surfaces:

The dorsal or internal surface (Fig. 42, _n_) looks into the cranial
cavity and is continuous with the dorsal surface of the wings. The
caudal end of the body is depressed, and when united to the basisphenoid
aids in forming the cranial wall of the sella turcica. At each
caudolateral angle is a short spine, the =anterior clinoid process=. At
about one-third the length of the bone from the caudal end is a
transverse groove (=chiasmatic groove=, Fig. 42, _m_) for the optic
chiasma. Its ends lead into two round foramina (the =optic foramina=,
Fig. 42, _l_; Fig. 21, _c_) which pass craniolaterad between the body
and the wings of the presphenoid and transmit the optic nerve and the
ophthalmic artery.

The ventral surface (Fig. 21) is hour-glass-shaped and marked by a
smooth median ridge, continuous with the ridge on the basisphenoid and
overlaid at its cranial end by the vomer. The caudal end presents a
rough triangular area on each side, for articulation with the pterygoid
process of the sphenoid bone, while the cranial end has similar areas
overlaid by the nasal portion of the palatine bones.

The lateral surface looks towards the orbitotemporal fossa. It is
notched near the caudal end by the ventral border of the optic foramen
(_c_). Caudad of this foramen the surface presents an oblique groove
which forms in the natural condition the medial boundary of the orbital
fissure.

Craniad of the optic foramen the surface is smooth and marked near its
ventral border by a longitudinal ridge which forms part of the dorsal
boundary of a fossa, the =external pterygoid fossa= (Fig. 40, _p_).

The caudal end presents ventrally a quadrangular rough surface for
articulation with the body of the sphenoid. The cranial end presents the
two sphenoidal sinuses separated by a median partition.

The median partition articulates by its free border with the lamina
perpendicularis of the ethmoid. At its ventral end is the abruptly
truncate end of the median ridge of the ventral surface, which is
continuous with the ventral cartilaginous portion of the lamina
perpendicularis. The lateral walls of the sphenoidal sinuses are
continued craniad of the dorsal and ventral walls and of the median
partition, and articulate ventrally with the nasal portion of the
palatine bones, and dorsally with the orbital plate of the frontal.
Between them is received the caudal ends of the labyrinths of the
ethmoid in the middle, while between their dorsal edges is received the
caudal end of the cribriform plate, and between their ventral edges the
expanded end of the vomer.

The =wings= (_b_) arise each from nearly the whole of the dorsolateral
angle of the body. They form prominent nearly horizontal triangular
projections over the optic foramina.

The dorsal and ventral surfaces are smooth and continuous respectively
with the dorsal and lateral surfaces of the body. The dorsal surface
looks into the cranial cavity, while the ventral looks into the
orbitotemporal fossa.

Craniad of the apex of the wing its border articulates with the ventral
edge of the orbital portion of the frontal bone. Caudad of the apex the
border articulates with the cranial border of the wing of the sphenoid.


=Temporal Bone.= =Os temporale= (Figs. 22 and 23).--This forms a part of
the lateral wall of the cranium, filling the gap between the occipital
and the sphenoidal segments. It is made up of three portions which are
distinct in kittens but somewhat firmly united in adult cats. In lower
vertebrates these portions are distinct bones called the =Squamous=, the
=Petrous=, and the =Tympanic= bones. In the cat they may be described as
the squamous (_a_), petrous (_b_), and tympanic (_c_) portions of the
temporal bone.

  [Illustration: FIG. 22.--TEMPORAL BONE, EXTERNAL SURFACE.

  FIG. 23.--TEMPORAL BONE, INTERNAL SURFACE.

  _a_, squamous portion; _b_, petrous portion; _c_, _c′_, tympanic
  portion (_c_, entotympanic; _c′_, ectotympanic); _d_, zygomatic
  process; _e_, mastoid portion of the petrous; _f_, mandibular fossa;
  _g_, postmandibular process; _h_, tuberculum articulare; _i_, external
  auditory meatus; _j_, stylomastoid foramen; _k_, pit for tympanohyal
  bone; _l_, mastoid process; _m_, grooves bounding the jugular foramen;
  _n_, internal auditory meatus; _o_, appendicular fossa; _p_, hiatus
  facialis; _q_, styliform process of tympanic bulla.]

The =squamous portion= (_a_) (=squama temporalis=) is thin and oval or
has the form of an equilateral triangle with rounded angles, with a
curved process, the =zygomatic process= (_d_), arising from its ventral
border. Its outer surface (Fig. 22) is convex and smooth and gives
origin to part of the temporal muscle. Its inner surface (Fig. 23) is
concave and smooth except near the margins, where it is bevelled and
rough. The roughened border is broader dorsad and caudad. The ventral
margin of the bone is turned mediad at its cranial end so that the
lateral face of the inverted portion looks ventrad. By this portion of
its lateral face the squamous rests upon the tympanic bulla, and its
edge articulates with the tentorium and the wing of the sphenoid. The
remaining (caudal) portion of the ventral border overlies the mastoid
portion (_e_) of the petrous. By the remainder of its border the bone
articulates with the parietal dorsad and with the wing of the sphenoid
craniad. The roughened portion of its inner surface overlies the margins
of both these bones.

The zygomatic process (_d_) is formed by the confluence of two roots.
One of these starts from the ventral end of the lambdoidal ridge and
passes along the ventral margin of the squama dorsad of the external
auditory meatus. The other arises abruptly from the cranioventral angle
of the bone. The process thus formed is at first broad and passes
horizontally laterad and slightly craniad. It soon grows more slender
and turns gradually craniad, while at the same time it twists so that
the surface which is dorsal at the base becomes medial at the tip; the
posterior root which is continuous with the caudal border at the base is
continuous with the dorsal border at the apex. On the ventral surface of
the base is a transversely elongated concave articular surface, the
=mandibular fossa= (_f_), for the condyloid process of the lower jaw.
Caudad of this is a sharp transverse ridge, the =postmandibular= or
=postglenoid process= (_g_), and craniad of the lateral end of the fossa
a slight tubercle, the =tuberculum articulare= (_h_). Near its apex the
zygomatic process is more slender and its ventral border is bevelled for
articulation with the malar or zygomatic bone.

The =tympanic= (Figs. 22 and 23, _c_; Fig. 24) is expanded into a large
hollow olive-shaped bone which is known as the =auditory bulla= and
encloses the tympanic cavity. Its substance is very compact. Unlike the
tympanic of most other mammals it is developed from two bones, known as
the =ectotympanic= (Fig. 22, _c′_) and =entotympanic= (_c_). These are
strongly marked in young kittens, and can usually be easily
distinguished in adult cats. The entotympanic (Figs. 22 and 23, _c_)
forms the larger part of the bulla, constituting its ventral and medial
surfaces; it is thin, smooth, and transparent. The ectotympanic (Fig.
22, _c′_) surrounds the external auditory meatus: it is thicker and more
opaque than the entotympanic. The bulla lies ventrad of the squamous,
and in an external view conceals a large part of the petrous.

On its lateral surface it presents near the dorsal border an irregular
oval opening, that of the =external auditory meatus= (Fig. 22, _i_),
which leads into the tympanic cavity. Caudad of the external auditory
meatus is a nearly dorsoventral groove, which, when the bone is
articulated, forms a part of the boundary of the stylomastoid foramen
(Fig. 22, _j_); just ventrad of this groove is a pit (_k_) which lodges
the tip of the tympanohyal bone.

Craniad the bone is produced into a short spine, the =styliform= process
(_q_), which lies in a horizontal groove in the ventral surface of the
basisphenoid. Laterad of this spine is a groove for the tuba auditiva or
Eustachian tube.

  [Illustration: FIG. 24.--TYMPANIC BULLA, ISOLATED, MEDIAL SURFACE.

  _a_, inner end of auditory meatus; _b_, partition dividing tympanic
  cavity; _c_, styliform process.]

The medial surface (Fig. 24) presents in the middle near its ventral
margin a short triangular spine which lies in the natural state against
the ventral surface of the basilar portion of the occipital.

Caudad of this spine the surface is marked by two or three vertical
parallel grooves (Fig. 23, _m_). They indicate the portion of the bone
which bounds the jugular foramen, and are possibly impressions of the
ninth, tenth, and eleventh nerves.

The dorsal two-thirds of the medial surface is lacking in the
disarticulated bulla (Fig. 24), so that the cavity of the bone is
exposed. This opening is in the natural state closed by the petrous
bone. The caudal end is rough where it is overlaid by the jugular
process.

On the inner surface of the tympanic bulla is seen the thickened margin
of the inner end of the auditory meatus (Fig. 24, _a_). To it is
attached the membrana tympana. In the median dorsal line this margin is
notched for the reception of the incus and head of the malleus. From the
lateral wall of the cavity at the line of junction of the ectotympanic
and entotympanic a thin bony partition (_b_) rises. It runs almost
directly mediad; is concave dorsally and divides the tympanic cavity
into two chambers.

=The Petrous Portion= (Fig. 23, _b_, and Fig. 25).--This consists of two
parts, a very dense part (the petrous portion proper, Fig. 25), which
has the form of a triangular pyramid and encloses the auditory
labyrinth, and a less dense part, the =mastoid= portion (Figs. 22 and
23, _e_), which is flattened and triangular and is attached by its base
to the base of the pyramid.

The petrous portion may be described as having a base and three sides,
lateral, dorsal, and medial. It completes the medial wall of the
tympanic bulla, so that it is not possible to see it from the exterior
of a skull except through the auditory meatus (Fig. 22, _i_). When the
bones of the skull are articulated its dorsal surface is covered by the
tentorium and alisphenoid. Its lateral face looks into the tympanic
cavity, while the medial face looks into the cranial cavity.

  [Illustration: FIG. 25.--PETROUS BONE OF RIGHT SIDE, LATERAL SURFACE,
  ENLARGED.

  _a_, fenestra cochleæ; _b_, promontory; _c_, fenestra vestibuli; _d_,
  fossa for the tensor tympani muscle; _e_, fossa for incus and malleus;
  _f_, fossa continuous with stylomastoid foramen; _g_, foramen leading
  to facial canal.]

Its lateral face (Fig. 25) (medial wall of the tympanic cavity) presents
just ventrad of the middle of its base a large circular foramen, the
=fenestra cochleæ= (_a_) (or fenestra rotunda), which looks
caudolaterad; it leads into the cochlea. The fenestra cochleæ lies at
the summit of a nipple-like elevation, the =promontory= (_b_), which is
continued toward the apex of the bone as a gradually diminishing
semicylindrical ridge, due to the presence within it of the bony
cochlea. Dorsad of the fenestra cochleæ is the much smaller =fenestra
vestibuli= (_c_) (or ovalis) which leads into the vestibule. It is
occupied in the natural condition by the base of the stapes.

Dorsocraniad of the fenestra vestibuli is a large fossa (_d_) which
contains the tensor tympani muscle. Dorsocaudad of this, partly bounded
by the squamous portion of the temporal, is another large fossa (_e_),
the cranial end of which is occupied by the incus, while its caudal end
is occupied by the head of the malleus.

Nearly caudad of this fossa and separated from it by an oblique bony
septum is a third fossa (_f_) which is narrow and curved. It is
continuous with a notch in the mastoid portion of the bone. When the
tympanic is articulated the notch is converted into a foramen
(=stylomastoid foramen=, Fig. 22, _j_) for the exit of the seventh
nerve. The fossa gives passage to the seventh nerve and also lodges the
stapedius muscle. A groove may be traced from the stylomastoid foramen
to the caudal border of the fossa for the tensor tympani muscle, where
it passes into a canal (_g_). The groove and canal are parts of the
=canalis facialis= or =facial canal= (aqueductus Fallopii) for the
passage of the seventh nerve through the petrous bone.

The medial surface (Fig. 23, _b_) of the petrous portion shows near its
middle a fossa, the =internal auditory meatus= (_n_). This is divided by
a partition of bone into a dorsal and ventral part. The dorsal portion
is the beginning of the facial canal (aqueductus Fallopii) by which the
seventh nerve passes through the petrous bone to emerge at the
stylomastoid foramen. The ventral portion shows at its bottom several
small foramina for the auditory nerve.

Dorsocaudad of the internal auditory meatus is a deep fossa (_o_) for a
small lobe, the so-called appendicular lobe, of the cerebellum. This may
be called the appendicular fossa.

The dorsal surface is triangular and presents near its apex a
foramen--the =hiatus facialis= (_p_), the opening of a canal which joins
the canalis facialis and transmits the superficial petrosal branch of
the nerve of the pterygoid canal (Vidian nerve). That part of the dorsal
surface which lies caudad of the hiatus facialis is known as the =tegmen
tympani=.

The base of the petrous is attached to the mastoid portion (Fig. 23,
_e_).

(For an account of the structures within the petrous bone and the
tympanic cavity, see the description of the internal and middle ear.)

The =mastoid portion= (Figs. 22 and 23, _c_) is attached by its base to
the pyramidal petrous portion, with which it forms an angle of about 120
degrees. It appears in the lateral wall of the skull between the
parietal bone and the occipital (Fig. 40, _d_). The lambdoidal ridge is
continued on its outer surface to the caudal border of the external
auditory meatus. Caudad of the stylomastoid foramen it forms a slight
nipple-like eminence, the =mastoid process= (Fig. 22, _l_). Its inner
face looks into the cranial cavity.


=Parietal Bone.= =Os parietale= (Figs. 39, 40, and 43, 3).--The parietal
bones form the larger part of the lateral and dorsal boundary of the
cranial cavity. Each is a thin rectangular bone, compact and curved and
with a deeply notched shelf of bone, the =tentorium= (Fig. 42, _e_, and
Fig. 43, _f_), projecting inward from near the caudal margin.

The outer surface is smooth and convex. The highest part of the
convexity, a little caudad of the middle of the bone, is known as the
=parietal tubercle= or =eminence= (Fig. 39, _d_); it marks the point of
beginning ossification. An obscure curved ridge (Fig. 39, _e_), running
from the caudodorsal angle or a point craniad of it craniolaterad,
indicates the boundary of the origin of the temporal muscle. Near the
ventral border the surface is roughened and is covered in the natural
state by a part of the squamous portion of the temporal bone.

The inner surface (Fig. 43, 3 and 3′) is smooth and marked by ridges and
grooves for the convolutions of the cerebrum. Near the medial border is
a ridge which, when the bone is articulated with that of the opposite
side, forms a shallow groove for the =superior sagittal sinus=.
Beginning near the middle of the ventral margin and passing dorsad is a
groove for the middle meningeal artery. The =tentorium= (Fig. 43, _f_)
arises from the inner surface near its caudal margin and projects mediad
as a thin curved or notched shelf of bone which separates the cerebellar
fossa (Fig. 43, _I_) of the cranium from the cerebral fossa (Fig. 43,
_II_). When the parietals are articulated there is left between the
tentoria a large foramen by means of which the two fossæ communicate.
The foramen is bounded laterally and dorsally by the free margins of
the tentoria, while the ventral end of each tentorium articulates with
the alisphenoid, and its dorsal end with the opposite tentorium.

The medial border is straight and is united by suture to the opposite
bone.

The cranial border is bevelled at the expense of the inner surface and
articulates with the frontal. Just ventrad of the middle of the border
projects a sharp spine which fits into a corresponding notch in the
caudal border of the frontal.

The ventral border is concave, sharp, and bevelled at the expense of the
outer surface, for articulation with the squamous portion of the
temporal, except near the cranial end, where it articulates with the
wing of the sphenoid.

The caudal border is thick and porous medially, but thin laterally, and
bevelled at the expense of the inner surface for articulation with the
interparietal and mastoid portion of the temporal.


=Frontal Bone.= =Os frontale= (Figs. 39, 40, and 41, 5; Fig. 43, 8; Fig.
26).--The frontal bones meet one another in the median dorsal line so as
to form the roof of the skull between the parietal and nasal bones. A
part extends also ventrad, forming a large part of the medial wall of
the orbit and a part of the temporal fossa.

The bone may be divided into two portions, a plate forming the cranial
portion of the roof of the skull and a part of the roof of the nasal
cavity, the =frontal plate= (Fig. 40, 5), and a part descending into the
orbit, the =orbital plate= (Fig. 40, 5′).

The frontal plate (Fig. 40, 5) is a right-angled triangle with the
hypothenuse lateral. Its dorsal surface is convex and smooth. The
cranial two-thirds of its lateral border is separated from the orbital
fossa by a ridge, the =supraorbital arch= or margin (Fig. 39, _i_; Fig.
40, _o_); the caudal third passes gradually into the temporal fossa. At
its cranial angle is a triangular projection, the =frontal spine= or
nasal spine (Fig. 26, _a_), which fits into a space between the nasal
and maxillary bones.

  [Illustration: FIG. 26.--FRONTAL BONE, MEDIAL SURFACE.

  _a_, frontal spine; _b_, transverse ridge; _c_, surface applied to the
  ethmoid; _d_, vertical plate of medial border.]

The ventral surface is concave and smooth over its caudal one-half and
helps to form the cranial part of the brain-case. It presents slight
ridges and depressions for convolutions of the cerebrum. At its narrowed
middle region the ventral surface is marked by a thick transverse ridge
(Fig. 26, _b_). Caudally the ridge descends by a gentle slope to the
level of the ventral surface of the bone. The cranial end of the ridge
is pierced by an oval foramen through which the frontal sinus (Fig. 43,
_m_, _m′_), which lies within the ridge, communicates with the spaces in
the ethmoid bone (nasal cavity). Craniad of the ridge the surface (Fig.
26, _c_) is rough and, together with the raised medial border of the
bone and the orbital plate, encloses a rectangular space which in the
natural state receives a portion of the labyrinth of the ethmoid. The
ventral surface is marked at its medial edge by a thin longitudinal
ridge which, when the bones are articulated, is continuous with one of
the vertical lamellæ of the ethmoid.

The medial border forms a vertical plate (_d_), broadest craniad and
roughened for articulation with its fellow of the opposite side except
at its cranial end, where it articulates with the border of the nasal
bone.

The caudal border is roughened, bevelled at the expense of the outer
surface, and articulated with the parietal bone except at its ventral
end, where it articulates with the alisphenoid.

The lateral border is smooth, and it is here that the orbital plate is
joined to the frontal plate at right angles. Along its cranial
two-thirds this union is marked by a sharp ridge, the supraorbital
margin (Fig. 40, _o_) or arch. This ridge extends caudolaterad as a
triangular projection, the =zygomatic= (or postorbital) =process= (Fig.
40, _n_), which is flattened on its cranioventral face near its
extremity and forms part of the boundary of the orbital fossa. At its
cranial end the lateral border articulates with the nasal and maxillary
bones.

The orbital plate (Fig. 40, 5′) arises from the ventral surface of the
lateral border of the frontal plate. It is directed ventrad, is smooth
and concave on its outer surface, and forms the dorsal portion of the
medial wall of the orbital fossa. Near its ventral border it bears the
small =ethmoidal foramen=, for the artery of the same name.

On the caudal one-half of its inner surface (Fig. 26) it assists the
caudal part of the dorsal plate in forming the brain-case. The cranial
one-half of its inner surface is marked off from the remainder of the
surface by a sharp irregular ridge which is for articulation with the
cribriform plate of the ethmoid. Craniad of this the surface is marked
by ridges and looks into the nasal cavity.

The cranial margin is produced dorsally in the form of a blunt
triangular spine. Mediad of this spine the bone articulates with the
lachrymal bone.

The ventral border articulates by its cranial one-third with the orbital
plate of the palatine, and by its caudal two-thirds with the body and
wing of the presphenoid.


=Maxillary Bone.= =Maxilla= (Figs. 27 and 28).--The maxillary bone forms
the cranial and lateral portions of the roof of the mouth. The bones of
opposite sides meet craniad, but diverge caudad to enclose the palatal
plates of the palatine bones. Each consists of a thick prismatic ventral
portion or body (_a_) and a thin flat plate, the =frontal process=
(_b_), extending dorsad from the cranial part of the bone.

  [Illustration: FIG. 27.--MAXILLARY BONE, LATERAL SURFACE.

  FIG. 28.--MAXILLARY BONE, MEDIAL SURFACE.

  _a_, body; _b_, frontal process; _c_, infraorbital foramen; _d_,
  elevation for root of canine tooth; _e_, canine tooth; _f_, first
  premolar; _g_, second premolar; _h_, third premolar; _i_, molar tooth;
  _j_, zygomatic process; _k_, beginning of lachrymal canal; _l_, ridge
  to which the ventral nasal concha is attached; _m_, nasal crest of
  palatine process.]

The body (_a_) has the form of a triangular prism whose broader dorsal
face looks into the nasal cavity and orbit, while the ventral face looks
into the mouth, and the lateral face toward the cheek. From the junction
of the dorsal and lateral surfaces at the cranial end the large flat
curved frontal process (_b_) passes dorsad, while the teeth are
implanted along the border, =alveolar border= or process, formed by the
junction of the ventral and lateral surfaces.

The lateral surface is continuous with the lateral surface of the
frontal process and shows at the base of the frontal process on its
caudal border the large =infraorbital= foramen (Fig. 27, _c_), for the
vessels and nerves of the same name. Near the medial end of the surface
is a cylindrical elevation (_d_) for the root of the canine tooth (_e_).

The ventral surface is smooth and looks into the roof of the mouth.

On the dorsal surface caudal and cranial halves may be distinguished.
The caudal one-half enters into the floor of the orbit. The lateral edge
of this portion is divided into two laminæ, between which is received
the end of the malar bone. Caudad this edge is prolonged into the short
dorsally directed =zygomatic process= (_j_). The cranial half of the
dorsal surface looks into the nasal cavity and is separated from the
caudal half by a sharp vertical lamina of bone which runs caudomediad
from the base of the nasal process. To the dorsal edge of this lamina
are articulated the lachrymal bone and a part of the palatine. At the
point where the lamina joins the base of the nasal process a foramen is
seen leading into a canal, the =nasolachrymal canal= (_k_). Craniad of
the lamina the surface is concave. Where it becomes continuous with the
inner edge of the frontal process there is attached to it a thin bone,
the =ventral nasal concha= (or maxilloturbinal), which is rolled into an
irregular spiral. The nasolachrymal canal opens ventrad of its cranial
end.

The cranial third of this part of the bone projects further mediad than
does the rest of the medial border, forming thus the broad =palatine
process=. This is rough on its medial edge for articulation with the
premaxillary and the palatine process of the opposite bone. This medial
edge rises also dorsally into a low ridge, the =nasal crest= (_m_),
which is roughened for articulation with the vomer. The caudal
two-thirds of the medial edge articulates with the palatine bone.

The cranial end of the bone articulates with the premaxilla.

The caudal end is smooth.

The frontal process (_b_) presents on its inner surface, which looks
into the nasal cavity, certain transverse ridges which are in relation
with the ethmoid bone. Its outer surface is smooth. By its cranial
border it articulates with the nasal bone dorsally and with the
premaxillary bone ventrally.

  [Illustration: FIG. 29.--PREMAXILLARY BONE, OBLIQUELY CRANIOLATERAL
  ASPECT.

  _a_, the three incisor teeth; _b_, palatal portion of the bone; _c_,
  nasal process.]

Its dorsal end articulates medially with the nasal spine of the frontal
bone, and caudally with the orbital plate of the same bone.


=Premaxillary Bone.= (=Os incisivum BNA.=) =Premaxilla= (Fig. 29).--The
premaxillary bones bear the incisor teeth and form the cranial portion
of the roof of the mouth.

Each consists of an irregular, horizontal =palatal portion= (_b_) and of
a perpendicular =nasal process= (_c_) which forms part of the lateral
boundary of the nares and enters into the formation of the lateral wall
of the nasal cavity.

The palatal portion has in its caudal border a deep notch for the
foramen incisivum or anterior palatine canal, which lies between it and
the maxillary and transmits blood-vessels and nerves. It articulates
with the maxillary bone by this border.

The medial border is raised into a thin crest of bone which, besides
forming the medial wall of the foramen incisivum or anterior palatine
canal, articulates by its medial border with the bone of the opposite
side, forming a sort of median trough (=sulcus palatinus=) which
projects dorsad into the nasal cavity and receives the ventral border of
the nasal septum. The caudal end of this border articulates laterad with
the maxilla, dorsad with the vomer.

Its craniolateral border bears the incisor teeth (_a_).

The nasal process (_c_) presents three surfaces, all elongated and
triangular; one, the medial surface, is smooth and concave and looks
into the nasal cavity. Its dorsal border is rough for articulation with
the nasal bone dorsad, and smooth ventrad where it aids in forming the
nares.

The lateral surface is smooth.

The caudal surface is rough for articulation with the maxillary bone.


=Nasal Bone.= =Os nasale= (Fig. 30).--The nasal bones fill the space
between the nasal process of the premaxillary, the frontal process of
the maxillary, and the nasal spine of the frontal bone (Fig. 39, 7).
They thus form part of the dorsal wall of the nasal cavity near the
middle line.

  [Illustration: FIG. 30.--NASAL BONE, DORSAL VIEW.]

Each may be described as consisting of two elongated triangular lamellæ,
one vertical, the other horizontal. The vertical lamella is curved
slightly ventrad and has its apex directed craniad. It is applied by its
medial surface against the vertical lamella of the opposite bone, the
two thus forming a median vertical partition, the =nasal crest= (Fig.
43, 12), which extends ventrad into the nasal cavity and, by joining the
dorsal edge of the lamina perpendicularis, helps to form the internasal
septum.

The horizontal lamella is attached to the dorsal margin of the vertical
lamella in such a way that its apex lies opposite the base of the
vertical lamella. It helps to roof in the nasal cavity, and by its base
forms a part of the dorsal boundary of the narial opening. By its
lateral margin it articulates with the nasal spine of the frontal at its
caudal end, with the frontal process of the maxillary at its middle, and
with the nasal process of the premaxilla at its cranial end. The lateral
angle of its base projects in a curved line which forms the dorsal part
of the lateral boundary of the narial opening.

From the lateral border of the horizontal lamella a bony plate curves
ventrad and mediad, enclosing a narrow fossa which receives a part of
the ethmoid. This is the =concha nasalis superior= (nasoturbinal bone).


=Ethmoid Bone.= =Os ethmoidale= (Figs. 31 and 32).--The ethmoid bone
closes in the cranial cavity at its cranial end and extends forward into
the nasal cavity, which it largely fills.

It consists of a median vertical portion, the =lamina perpendicularis=
(Fig. 43, _n_; Fig. 42, _p_), forming a part of the nasal septum, of two
lateral portions made of thin sheets of bone variously folded and
united--the =labyrinths= (or ethmoturbinals), which fill the greater
part of the nasal cavity; and of a transverse perforated plate, the
=cribriform plate= (lamina cribrosa), attached to the caudal end of the
lamina perpendicularis and the labyrinths.

The lamina perpendicularis (Fig. 43, _n_; Fig. 42, _p_) is a flat
four-sided bone. By its caudal margin it is continuous with the
cribriform plate; by its ventral margin it is enclosed by the halves of
the vomer; by its dorsal margin it unites with the crest formed by the
vertical portion of the nasal bone craniad and with the vertical lamina
of the medial margin of the frontal caudad, while its cranial margin is
continued into the septal cartilage of the nose. Its lateral faces are
smooth and free.

The lamina cribrosa or cribriform plate (Fig. 42, _o_) is elongated
heart-shaped, with the apex of the heart ventrad. Its caudal face is
concave and looks into the cranial cavity. It presents three irregular
longitudinal rows of holes, one median and two lateral, for the passage
of the olfactory fibres from the cranial cavity into the nasal cavity.
Its cranial face is continuous along the medial line with the lamina
perpendicularis, and at the sides with the labyrinths.

The notch in the heart is directed dorsad and receives the vertical
lamina of the medial border of the frontal bone. The apex of the heart
articulates with the cranial end of the dorsal surface of the
presphenoid. Its lateral margins are articulated with the ethmoidal
ridges on the medial surface of the frontal bone.

  [Illustration: FIG. 31.--ETHMOID AND VOMER, SIDE VIEW.

  FIG. 32.--ETHMOID AND VOMER, VENTRAL VIEW.

  _a_, vomer; _b_, vertical cells of the labyrinth of the ethmoid; _c_,
  horizontal cell of the same; _d_, part of the ethmoid that forms the
  lamina papyracea; _e_, edge of cribriform plate.]

The labyrinths (Figs. 31 and 32) are attached to the cranial face of the
lamina cribrosa, one on each side of the lamina perpendicularis. Each is
made of thin bony plates irregularly folded so as to enclose spaces, the
=ethmoid cells=. In each may be distinguished a cranial portion (_b_),
in which the cells are nearly vertical, and a caudal portion (_c_), in
which the cells are nearly horizontal.

The medial surfaces are separated by a space from the lamina
perpendicularis. This space is broadest along the junction of the
horizontal and vertical portions of the labyrinth. There are thus formed
two passageways which correspond to the superior meati of human anatomy.

The lateral surfaces come into contact with the frontal process of the
maxillary and the orbital plate of the frontal bone. On the lateral
surface of each labyrinth there is a thin irregular lamina of bone lying
in a dorsoventral longitudinal plane and closing in some of the ethmoid
cells laterally (_d_). A small part of this lamina, situated near the
caudoventral angle of the bone, appears in the orbital fossa on the
external surface of the skull between the presphenoid, palatine, and
frontal bones or between the lachrymal, palatine, and frontal bones.
Sometimes in the entire skull two such pieces may be seen, one in each
of these positions. This corresponds to the =lamina papyracea= of human
anatomy.

The dorsocaudal angle of each bone is received into the space between
the orbital plate of the frontal and the vertical lamina of the medial
border of the frontal. Its ventrocaudal angle is received between the
cranial extensions of the lateral walls of the presphenoid, while its
ventral surface is overlaid caudally by the expanded portion of the
vomer, to which it is attached at its caudolateral angles.


=Vomer= (Figs. 31 and 32, _a_).--The vomer consists of two thin laminæ
of bone which ensheath the ventral margin of the lamina perpendicularis
(or the cartilaginous plate which continues ventrad from this margin)
and unite ventrad of it; the two thus form a trough open dorsad.

Each becomes horizontal near its caudal end and at the same time
expands. The expanded portion lies ventrad of the labyrinth of the
ethmoid, closing in some of its cells: its lateral angles are united
with the labyrinths.

At its caudal end the bone articulates with the body of the presphenoid,
and each half of it is produced caudad near the middle line into a
triangular spine which lies ventrad of the body of the presphenoid. The
horizontal portion of the bone helps to separate the olfactory and
respiratory passages of the nasal chamber, while its vertical portion
contributes to the formation of the nasal septum.

The ventral margin formed by the junction of the two halves of the bone
is smooth and free caudad, but at its cranial end is broad and rough for
articulation with the palatal processes of the maxillæ.


=Palatine Bone.= =Os palatinum= (Fig. 33).--The palate bone or palatine
bone consists of two portions, a =horizontal= or =palatal= portion (_a_)
and a =perpendicular= or =nasal= portion (_b_), uniting at an angle of
about forty-five degrees.

  [Illustration: FIG. 33.--PALATINE BONE, DORSAL VIEW.

  _a_, horizontal portion; _b_, perpendicular portion; _c_, maxillary
  spine; _d_, posterior nasal spine; _e_, sphenopalatine foramen; _f_,
  caudal opening of posterior palatine canal.]

The horizontal portions (_a_) of the two bones are received between the
maxillary bones and form the caudal and medial part of the roof of the
mouth. Each is irregularly quadrilateral in form, with the caudolateral
angle produced caudad into a long process which is continuous with the
perpendicular portion of the bone. The lateral margin of the horizontal
portion articulates over its cranial half with the maxillary bone. At
about its middle a short thick =maxillary spine= (_c_) projects
caudolaterad. The remainder of the lateral margin is directly continuous
with the perpendicular plate of the bone. The medial margin is rough for
articulation with the corresponding margin of the opposite palatine; the
caudal angle of this margin projects caudad as the short =posterior
nasal spine= (_d_). The caudal margin forms a free edge which bounds the
choanæ; it passes laterally into the perpendicular portion.

The ventral surface (Fig. 41, 8) looks into the mouth. Near the middle
of its craniolateral margin are two or more small foramina (Fig. 41,
_q_) which form the cranial termination of the posterior palatine canal.
The dorsal surface is smooth and looks into the nasal cavity.

The perpendicular or nasal portion (Fig. 33, _b_) of the palatine is
thin and irregularly quadrilateral in form. It is attached by its
cranial two-thirds to the dorsal surface of the horizontal portion. The
outer surface is concave and looks into the orbital fossa. The inner
surface is convex and looks into the nasal cavity.

The perpendicular portion is marked by two foramina just craniad of the
middle. The larger dorsal oval foramen is the =sphenopalatine= foramen
(_e_). The smaller ventral foramen is the caudal opening of the
posterior palatine canal (_f_). From this opening the canal passes
craniomediad, lying in the substance of the palatine bone; it opens on
the ventral surface of the horizontal portion at the small openings
previously described (Fig. 41, _q_).

By its cranial margin it articulates with the lachrymal bone. By its
dorsal margin it articulates craniad with the orbital plate of the
frontal: with the lamina papyracea at its middle, and with the body of
the presphenoid caudad. The caudal half of the dorsal margin is
partially divided into two lamellæ with a rough surface between them:
this rough surface lies against the ventral surface of the presphenoid.
The caudal margin articulates with the pterygoid portion of the
sphenoid.


=Lachrymal Bone.= =Os lachrymale= (Fig. 34; Fig. 39, 10).--The lachrymal
bone is a thin pentagonal scale of bone filling the interval between the
horizontal plate of the palatine, the maxillary, and the orbital plate
of the frontal. Its outer surface looks into the orbit, its inner
surface into the nasal cavity.

  [Illustration: FIG. 34.--LACHRYMAL BONE OF LEFT SIDE, EXTERNAL
  SURFACE.

  FIG. 35.--MALAR BONE OF RIGHT SIDE, LATERAL SURFACE.

  Fig. 34.--_a_, notch forming the beginning of the lachrymal canal.

  Fig. 35.--_a_, ridge for origin of the masseter muscle; _b_, frontal
  process; _c_, zygomatic process.]


Near the middle of its cranial border it is notched obliquely by a
foramen (_a_), the beginning of the nasolachrymal canal.


=Malar Bone.= =Jugal Bone.= =Os zygomaticum= (Fig. 35).--The malar or
zygomatic bone is a flat curved plate of bone which forms the lateral
wall of the orbit and together with the zygomatic process of the
temporal forms the zygomatic arch. Its outer surface is smooth and
marked by a longitudinal ridge (_a_) for attachment of the masseter
muscle.

At its caudal end the bone is continued into two processes: one, the
=frontal= process or =orbital= process (_b_), is a triangular spine of
bone directed caudomediad; when the bones are articulated it lies
opposite the zygomatic process of the frontal to which it is joined by a
ligament (orbital ligament). The other, =zygomatic= process (_c_) of the
malar bone, extends ventrocaudad and articulates with a similar process
from the temporal to form the zygomatic arch above mentioned.

Its inner surface is smooth and looks into the orbit, except that of the
zygomatic process, which looks into the temporal fossa.

Its cranial border is roughened at the expense of both surfaces and
articulates with the maxillary bone. Its other borders are smooth except
the dorsal border of the zygomatic process, which is roughened for
attachment to the zygomatic process of the temporal.


=The Mandible.= =Mandibula= (Figs. 36 and 37).--The mandible (or
inferior maxillary bone) is composed of two halves which come together
at the cranial end and form the lower jaw. At its caudal end each half
articulates with the temporal bone at the mandibular fossa, and at its
cranial end it joins the opposite bone, the suture being known as the
=symphysis= of the jaw (=symphysis menti=) (Fig. 37, _a_).

Each half consists of a horizontal portion, the =body= (_b_), bearing
teeth on one of its borders (the =alveolar border=), and of a vertical
portion, the =ramus= (_c_).

The body (_b_) has the form of a flattened cylinder and has two surfaces
and two borders. The lateral surface (Fig. 36) is smooth and presents
near its cranial end a foramen (or sometimes two), the =mental foramen=
(_d_), forming the cranial termination of the mandibular canal. At its
caudal end is a deep fossa continuing on to the ramus, the =coronoid
fossa=, or =masseteric fossa= (_e_).

  [Illustration: FIG. 36.--MANDIBLE, LATERAL SURFACE.

  FIG. 37.--MANDIBLE, MEDIAL SURFACE.

  _a_, symphysis; _b_, body; _c_, ramus; _d_, mental foramina; _e_,
  coronoid fossa; _f_, mandibular foramen; _g_, angular process; _h_,
  coronoid process; _i_, condyloid process; 1, 2, 3, the three incisor
  teeth; 4, the canine tooth; 5, 6, the premolars; 7, the molar tooth.]

The medial surface (Fig. 37) is smooth and has near its caudal end a
foramen, the =mandibular foramen= (_f_), which communicates with the
mandibular canal leading lengthwise through the bone to the mental
foramen. The cranial end is roughened for attachment to the bone of the
opposite side.

The ventral border is smooth and rounded; it ends caudally in a blunt
point, the =angular process= (_g_). The dorsal (alveolar) border is
slightly curved and bears the sockets (=alveoli=) for the teeth. It is
continuous with the cranial margin of the coronoid process.

The ramus is divided into two portions, the =coronoid= process (_h_) and
the =condyloid= process (_i_). The coronoid process (_h_) extends
dorsocaudad as a thin plate of bone with smooth surfaces and borders.
Its outer surface is partly occupied by the =coronoid fossa= (_e_). The
condyloid process (_i_) has the form of a semicylindrical transverse
piece of bone attached to the caudal margin of the coronoid process. It
articulates with the mandibular fossa of the temporal bone.


=Hyoid Bone.= =Os hyoideum= (Fig. 38 and Fig. 104).--The hyoid bone
forms the support for the tongue and gives origin to muscles passing to
the tongue and larynx. It also supports the thyroid cartilage (Fig. 104,
1).

  [Illustration: FIG. 38.--HYOID BONE, DORSAL VIEW.

  _a_, body; _b_, _c_, _d_, _e_, cranial cornu; _f_, caudal cornu; _b_,
  ceratohyal; _c_, epihyal; _d_, stylohyal; _e_, tympanohyal; _f_,
  thyrohyal.]

It consists of a transverse bony bar, the =body= (Fig. 38, _a_) and of
two =cornua= or horns attached to each end of the body.

The cranial cornu (lesser cornu of human anatomy) is the longer (Fig.
38, _b_-_e_). Each arises from the cranial face of the body at its
lateral end, curves laterad, and then caudodorsad. It consists of four
bony pieces movably united by cartilage.

The terminal piece is the =tympanohyal= (_e_); it is imbedded in the
tympanic bulla just ventrad of the stylomastoid foramen. It is not
therefore seen attached to the cornu after the latter has been separated
from the skull. The other pieces become successively shorter toward the
body, and are called =stylohyal= (_d_), =epihyal= (_c_), and
=ceratohyal= (_b_).

The caudal cornua (_f_) (greater cornua of human anatomy) arise from the
ends of the body. Each consists of a single piece of bone, the
=thyrohyal= (_f_), which passes caudolaterad; its free end is united to
a process of the thyroid cartilage (Fig. 104, 1).


=The Skull as a Whole.=--In the following description of the skull as a
whole the mandible, hyoid, and ear-bones are not included.

The skull forms a bony box which contains the brain and is produced
craniad into the =facial= portion which encloses the nasal cavity and
forms the framework of the face.

In =dorsal view= (Fig. 39) the skull presents a smooth convex surface,
broadest caudad, with the two =zygomatic arches= (_g_) curving out some
distance laterally. The following bones are visible in dorsal view: the
occipital (1), interparietal (2), parietals (3), temporals (4), frontals
(5), malar or zygomatic bones (6), nasals (7), maxillaries (8),
premaxillaries (9), and lachrymals (10).

  [Illustration: FIG. 39.--SKULL, DORSAL SURFACE.

  1, occipital bone; 2, interparietal bone; 3, parietal bones; 4,
  temporal; 5, frontal; 6, malar; 7, nasal; 8, maxillary; 9,
  premaxillary; 10, lachrymal, _a_, lambdoidal ridge; _b_, external
  occipital tubercle; _c_, sagittal crest; _d_, parietal eminence; _e_,
  line which forms the dorsal boundary of the temporal fossa; _f_,
  zygomatic process of the frontal; _g_, zygomatic arch; _h_, frontal
  process of the malar; _i_, supraorbital arch; _j_, nares; _k_, foramen
  incisivum or anterior palatine foramen; _l_, sphenopalatine foramen;
  _m_, zygomatic process of the temporal; _n_, infraorbital foramen;
  _o_, opening of lachrymal duct.]

The caudal boundary of the dorsal surface is marked by the prominent
=lambdoidal ridge= (_a_) which passes from the middle cranioventrad
along each side to the root of the zygomatic arch: it is borne by the
occipital and temporal bones. From the middle of the lambdoidal ridge a
second ridge, the =sagittal crest= (_c_), passes craniad in the middle
line across the interparietal bone: it varies greatly in extent,
reaching in a very old and muscular cat to the cranial border of the
parietals, while in kittens it does not exist. The most prominent
portions of the skull in this region, just craniad of the middle of the
parietal bones, are known as the parietal tubercles or eminences (_d_).
A faint curved line (_e_) runs from the cranial end of the sagittal
crest craniolaterad to the base of the zygomatic process of the
frontal: it marks the dorsal boundary of the origin of the temporal
muscle, and may therefore be considered the dorsal boundary of the
temporal fossa. This fossa extends from its dorsal boundary as far
laterad and caudad as the lambdoidal ridge (_a_), and as far craniad as
a line connecting the tip of the zygomatic process of the frontal (_f_)
with the frontal process of the malar (_h_). The temporal muscle takes
origin from its surface.

The middle portion of the dorsal surface is formed by the frontals (5).
Each frontal presents laterally a prominent =zygomatic process= (_f_),
extending ventrolaterad toward a corresponding (frontal) process (_h_)
of the malar bone. These two processes mark the boundary between the
orbital fossa (craniad) and the temporal fossa (caudad). Craniad of the
zygomatic process of the frontal a sharp margin separates the dorsal
surface of the skull from the wall of the orbital fossa: this is the
=supraorbital arch= or margin (_i_).

The cranial portion of the dorsal surface is formed by the maxillary
(8), nasal (7), and premaxillary bones (9). Just craniad of the nasals,
bounded ventrad and craniad by the premaxillaries, appears the large
opening of the nares (_j_), leading into the nasal cavity.

The =zygomatic arch= (_g_) is formed by the zygomatic process of the
temporal (_m_) and the malar or zygomatic bone (6). Each presents near
its middle a prominent dorsocaudally directed process, the frontal
process (_h_) of the malar bone. The zygomatic arch forms the lateral
boundary of the temporal and orbital fossæ, which are separated by a
line connecting the frontal process of the malar (_h_) and the zygomatic
process of the frontal (_f_).

A portion of the floor of the orbit and the opening of the lachrymal
canal (_o_) may also be seen in dorsal view; they are described in
connection with the lateral surface.

The =caudal surface= of the skull is formed largely by the occipital
bone (Fig. 17), surrounding the foramen magnum (Fig. 17, _d_). At the
sides of the foramen magnum are the two prominent curved occipital
condyles (_e_) for articulation with the atlas. Craniolaterad of the
condyles, separated from them by a deep notch, are the jugular processes
(_f_) of the occipital, closely applied to the caudal ends of the
tympanic bullæ.

Dorsad of the foramen magnum are faint indications of a median ridge
running dorsad, the =external occipital crest= (Fig. 17, _i_); this
rises at its junction with the lambdoidal ridge to form the prominent
=external occipital tubercle= (Fig. 39, _b_). The dorsal and
dorsolateral boundaries of the posterior surface are formed by the
lambdoidal ridge (Fig. 17, _h_; Fig. 39, _a_).

The =lateral surface= of the skull (Fig. 40) is much more complicated
than the dorsal and posterior surfaces. Caudally the occipital condyles
(_a_) and external occipital crest (_b_) are visible; dorsocaudad the
sagittal crest (_c_).

Extending from the caudal end of the sagittal crest the lambdoidal ridge
(_d_) is seen passing ventrocraniad to the tympanic bulla, thence
craniad to the root of the zygomatic arch. In the ventral part of the
caudal region the tympanic bulla (_e_) is visible with the jugular
process (_f_) of the occipital pressed close against its caudal end.
Just craniad of the jugular process the mastoid process (_g_) of the
temporal rests against the side of the bulla. Beneath the cranial edge
of this process is the opening of the stylomastoid foramen (_h_) for the
seventh nerve, while just ventrad of the foramen is the small pit (_i_)
in the tympanic bulla for the reception of the tympanohyal bone. Craniad
of the stylomastoid foramen is the large opening of the external
auditory meatus (_j_), leading into the middle ear.

Immediately dorsocraniad of the external auditory meatus the zygomatic
arch begins as the zygomatic process (_k_) of the temporal bone. On the
cranial surface of the base of this process is the deep mandibular fossa
(_l_) for the condyle of the mandible. This fossa is bounded caudally by
the prominent postmandibular process (_m_).

  [Illustration: FIG. 40.--SKULL, SIDE VIEW.

  1, occipital bone; 2, interparietal; 3, parietal; 4, temporal; 5, 5′,
  frontal; 6, malar; 7, sphenoid; 8, palatine; 9, presphenoid; 10,
  maxillary; 11, nasal; 12, premaxillary; 13, incisor teeth; 14, canine;
  15, 16, 17, premolars; 18, molar. _a_, occipital condyle; _b_,
  external occipital crest; _c_, sagittal crest; _d_, lambdoidal ridge;
  _e_, tympanic bulla; _f_, jugular process; _g_, mastoid process; _h_,
  stylo-mastoid foramen; _i_, pit for tympanohyal bone; _j_, external
  auditory meatus; _k_, zygomatic process of temporal bone; _l_,
  mandibular fossa; _m_, postmandibular process; _n_, zygomatic process
  of the frontal; _o_, supraorbital margin; _p_, external pterygoid
  fossa; _q_, sphenopalatine foramen; _r_, orbital fissure; _s_,
  internal pterygoid fossa; _t_, hamulus; _u_, foramen ovale; _v_,
  foramen rotundum; _w_, optic foramen; _x_, opening of lachrymal canal;
  _y_, infraorbital foramen.]

All that portion of the lateral surface of the skull which lies
craniodorsad of the lambdoidal ridge may be divided (excluding the
zygomatic arch) into three main parts, the =temporal fossa=, the
=orbital fossa=, and the =face=. The boundaries of the temporal fossa
have been given. The orbital fossa is bounded externally by a prominent
semicircular ridge formed chiefly by the zygomatic arch, the zygomatic
process of the frontal (_n_), and the supraorbital arch (_o_) of the
frontal, which may be traced to the cranial root of the zygomatic arch.
The orbital fossa may be considered to end caudally and ventrally at the
level of the optic foramen (_w_); ventrad of it are certain smaller
fossæ. Immediately ventrad is the long =external pterygoid fossa= (_p_),
from which arises part of the external pterygoid muscle. This fossa
begins at the sphenopalatine foramen (_q_) and extends caudad to the
orbital fissure (_r_); it is separated by a ridge from the orbital
fossa. Caudoventrad of the external pterygoid fossa and separated from
it by a sharp ridge is the small narrow =internal pterygoid= fossa
(_s_), which extends ventrad without interruption on to the surface of
the hamulus (_t_) and caudad to within two or three millimeters of the
tympanic bulla. From it the internal pterygoid muscle takes origin. The
hamulus (_t_) projects caudoventrad in this region, forming a prominent
feature in a lateral view.

Four foramina leading into the cranial cavity are visible in a lateral
view of the skull, craniad of the tympanic bulla. The one nearest the
bulla is the =foramen ovale= (_u_) for the third division of the fifth
nerve; next craniad of this is the =foramen rotundum= (_v_) for the
second division of the fifth nerve. These two foramina pierce the
alisphenoid: just craniad of them, between the alisphenoid and the
orbitosphenoid, is the large =orbital fissure= (_r_) (foramen lacerum
anterius), which transmits the third, fourth, and sixth cranial nerves
and the first division of the fifth. Dorsocraniad of the orbital fissure
is the =optic foramen= (_w_), for the =optic nerve=.

Ventrad of the cranial portion of the orbit is the large =sphenopalatine
foramen= (_q_), for the nerves and arteries of the same name. Just
craniad of this is the small caudal opening of the =posterior palatine
canal=, which passes through the substance of the palatine bone and
opens on its ventral surface near its cranial margin. Just dorsad of the
cranial root of the zygomatic arch is the opening of the =lachrymal
canal= (_x_), while the root of the arch is pierced by the large
=infraorbital foramen= (_y_), which transmits the =infraorbital= nerves
and artery from the orbit.

The teeth (13-18), implanted along the alveolar border of the maxillary
and premaxillary, form a prominent feature in a lateral view: they are
described in the account of the alimentary canal.

The =ventral surface= of the skull (Fig. 41) is very complex. It is
separated by the orbits into a caudal and a cranial portion, united by a
narrow median trough-like part. Laterad of this trough-like part are
visible parts of the orbit and the zygomatic arches, which do not
properly belong to the ventral surface and have already been described.

  [Illustration: FIG. 41.--SKULL, VENTRAL VIEW.

  1, occipital bone; 2, temporal; 3, sphenoid; 4, presphenoid; 5,
  frontal; 6, malar; 7, vomer; 8, palatine; 9, maxillary; 10,
  premaxillary. _a_, foramen magnum; _b_, occipital condyles; _c_,
  jugular process; _d_, tympanic bulla; _e_, mastoid process; _f_,
  stylomastoid foramen; _g_, external auditory meatus; _h_, jugular
  foramen; _i_, styliform process; _j_, groove for Eustachian tube; _k_,
  foramen ovale; _l_, foramen rotundum; _m_, pterygoid process of
  sphenoid; _n_, perpendicular plate of palatine; _o_, choanæ or
  posterior nares; _p_, zygomatic arch; _q_, cranial end of posterior
  palatine canal; _r_, palatine grooves; _s_, foramina incisiva or
  anterior palatine foramina; _t_, opening of pterygoid canal.]

Caudally there appear in the ventral view the foramen magnum (_a_),
occipital condyles (_b_), and jugular processes (_c_). In front of the
jugular processes the two tympanic bullæ (_d_) form prominent features,
with the mastoid process (_e_), the stylomastoid foramen (_f_), and the
external auditory meatus (_g_) on their lateral surfaces. All these
structures have been described. The tympanic bullæ (_d_) are placed with
long axes directed craniomediad, so that they converge toward their
cranial ends. At the caudomedial angle of each bulla is the large
=jugular foramen= (_h_), for the ninth, tenth, and eleventh nerves.
Opening into the mediocaudal margin of the jugular foramen is the
smaller =hypoglossal= foramen, for the twelfth nerve.

The craniomedial end of the tympanic bulla projects craniad as the
=styliform= process (_i_). Just laterad of this process is the opening
(_j_) into the tympanic bulla by which the tuba auditiva or Eustachian
tube passes into the middle ear. A faint groove for the tube passes
craniomediad from this opening, on the surface of the sphenoid.
Craniolaterad of the opening for the tuba auditiva is the =foramen
ovale= (_k_); craniad of this the =foramen rotundum= (_l_) is faintly
indicated. On the surface of the sphenoid just craniad of the styliform
process of the bulla tympani is the minute opening of the =pterygoid
canal= (_t_). The orbital fissure and optic foramen are not seen in the
ventral view.

The middle region of the ventral surface is narrow: it is formed by a
trough-like fossa which is bounded laterally by the pterygoid processes
(_m_) of the sphenoid and the perpendicular plates of the palatines
(_n_). Ventrad of this lies, in the natural condition, the soft palate,
converting the fossa into the nasal portion of the pharynx or
nasopharynx. Craniad this fossa is bounded by the free caudal edges of
the palatines; beneath which the fossa communicates with the nasal
cavity by the two choanæ (_o_). Laterad of this median fossa are visible
in the ventral view parts of the temporal and orbital fossæ, bounded
laterally by the zygomatic arches (_p_).

The cranial part of the ventral surface is a somewhat triangular plane
area formed by the palatal portions of the palatines (8), maxillaries
(9), and premaxillaries (10), which together constitute the hard palate
(=palatum durum=). Laterad and craniad this area is bounded by the
alveolar borders of the maxillaries and premaxillaries bearing the
teeth. The hard palate is marked near the cranial border of the palatine
bones with two or more foramina which form the cranial termination of
the posterior palatine canal (_q_). Two faint grooves pass from these
foramina a short distance craniad, gradually converging: these are known
as the =palatine grooves= (_r_) (=sulci palatini=). Near the cranial end
of the hard palate are two large openings close together near the middle
line: these are the =foramina incisiva= (or =anterior palatine
foramina=) (_s_).

  [Illustration: FIG. 42.--SKULL, WITH DORSAL SURFACE REMOVED, SHOWING
  THE CRANIAL AND NASAL CAVITIES.

  _a_, foramen magnum; _b_, caudal end of hypoglossal canal; _c_,
  jugular foramen; _d_, internal auditory meatus; _e_, tentorium,
  forming the cranial boundary of the cerebellar fossa; _f_, dorsum
  sellæ; _g_, sella turcica; _h_, anterior clinoid processes; _i_,
  foramen ovale; _j_, foramen rotundum; _k_, orbital fissure; _l_, optic
  foramen; _m_, chiasmatic groove; _n_, presphenoid bone; _o_,
  cribriform plate; _p_, lamina perpendicularis of ethmoid; _q_,
  labyrinths of ethmoid; _r_, nares; _s_, foramina incisiva or anterior
  palatine foramina; _t_, infraorbital foramen; _u_, opening of the
  lachrymal canal; _v_, caudal opening of posterior palatine canal; _w_,
  sphenopalatine foramen; _x_, frontal process of the malar; _y_,
  zygomatic process of the temporal; _z_, appendicular fossa, in the
  petrous bone.]


=Cavities of the Skull= (Figs. 42 and 43).--The bones of the cranial
portion of the skull enclose the =cranial cavity= for the brain; the
facial bones enclose the =nasal cavity=, for the olfactory organ.

The =cranial= cavity is divisible into three principal fossæ: the
=cerebellar= fossa (Fig. 43, _I_) caudad, for the cerebellum; the
=cerebral= fossa (_II_) in the middle, for the cerebrum; the small
=olfactory= fossa (_III_) at the cranial end for the olfactory bulb of
the brain.

The =cerebellar= fossa (_I_) is bounded caudally by the occipital bone
enclosing the foramen magnum (Fig. 42, _a_). Its ventral surface is
formed by the basilar portion of the occipital and the petrous portions
of the temporals; its lateral surface by the mastoid portions of the
temporals and parts of the parietals and occipital. Its roof is formed
by the parietals and interparietal. Craniad the cerebellar fossa is
partly separated from the cerebral fossa by the tentorium (Fig. 42, _e_;
Fig. 43, _f_) formed by the two parietals: this encloses a quadrangular
opening by which the two fossæ communicate. The caudal, dorsal, and
lateral walls of the cerebellar fossa are deeply marked by fossæ for the
lobes of the cerebellum; the small =appendicular= fossa (Fig. 43, _e_),
forming a deep indentation in the petrous bone near its dorsocaudal end,
is particularly noticeable.

The following openings are found in the walls of the cerebellar fossa.
Caudad is the large foramen magnum (Fig. 42, _a_) by which the
brain-cavity communicates with the vertebral canal. Near the caudal
margin of the foramen magnum, on its lateral side, just mediad of the
dorsal end of the occipital condyle, is the caudal opening of the
condyloid canal (Fig. 43, _a_) which passes craniad through the
substance of the occipital bone to open just caudad of the petrous: it
transmits a vein. The condyloid canal varies greatly in size in
different specimens. A few millimeters craniad of the edge of the
foramen magnum on the floor of the fossa is the small opening of the
hypoglossal canal (Figs. 42 and 43, _b_), for the twelfth nerve. Just
craniad of this, at the caudomedial border of the petrous, is the large
jugular foramen (_c_). On the petrous itself, near the middle, is the
internal, auditory meatus (_d_) divided into the dorsal =facial canal=
for the seventh nerve, and a ventral passage for the eighth nerve. At
the cranial end of the cerebellar fossa is the large opening bounded by
the free edges of the tentorium.

The =cerebral= fossa forms much the largest part of the cranial cavity.
It is bounded by the parietals (Fig. 43, 3′), squamous portions of the
temporals (4), frontals (8), the sphenoid (5), and presphenoid (6). A
slight rounded ridge on its lateral wall at about the position of the
suture between the frontals and parietals separates a smaller cranial
portion sometimes called the =anterior= fossa, from a larger caudal
portion sometimes known as the =middle= fossa of the cranial cavity. The
walls of the cerebral cavity are marked with numerous ridges and
shallow furrows for the cerebral convolutions.

The floor of the cerebral cavity is bounded caudad by the prominent
dorsum sellæ (Fig. 42, _f_; Fig. 43, _g_), just craniad of which is the
rounded depression known as the sella turcica (Fig. 42, _g_; Fig. 43,
_h_), for lodgment of the hypophysis. A number of foramina pierce the
floor of the cavity in this region. Just ventrad of the cranial tip of
the petrous portion of the temporal is the small =foramen lacerum=
(medius). Craniad and laterad of this is a row of four foramina: the
caudal one is the foramen ovale (Fig. 42, _i_); then come in order the
foramen rotundum (_j_), the orbital fissure (_k_), and the optic foramen
(Fig. 42, _l_; Fig. 43, _k_). The two optic foramina are connected by
the shallow transverse =chiasmatic groove= (Fig. 42, _m_), for the optic
chiasma. Another small foramen continues caudad from a groove on the
floor of the orbital fissure; this opens on the ventral surface of the
sphenoid, between the wing and the body of the bone. The groove and
foramen constitute the =pterygoid canal=, which transmits a nerve,--the
=nerve of the pterygoid canal=, or Vidian nerve.

The cranial cavity narrows at its cranial end to form the small
=olfactory= fossa (Fig. 43, _III_) which lodges the olfactory bulbs.
This is bounded by the frontals and the lamina cribrosa (Fig. 42, _o_)
of the ethmoid; caudad it opens directly into the cerebral fossa.
Numerous openings through the lamina cribrosa for the olfactory fibres
connect the olfactory fossa with the nasal cavity. The roof of the fossa
is marked by a prominent median crest from the united edges of the
frontals.

The =nasal= cavity is almost completely filled by the ethmoid and vomer
and the conchæ nasales. Its roof is formed by the nasal bones and
portions of the frontals; its sides by the frontals, lachrymals,
maxillaries, premaxillaries, and palatine bones; its floor by the
horizontal plates of the palatines, maxillaries, and premaxillaries.

  [Illustration: FIG. 43.--SKULL, MEDIAN LONGITUDINAL SECTION, SHOWING
  THE CAVITIES.

  _I_, cerebellar fossa; _II_, cerebral fossa; _III_, olfactory fossa.
  1, occipital bone; 2, interparietal; 3, 3′, parietal; 4, temporal (4,
  squamous portion; 4′, petrous portion; 4″, tympanic portion); 5,
  sphenoid; 6, presphenoid; 7, palatine; 8, frontal; 9, maxillary; 10,
  premaxillary; 11, ethmoid; 12, nasal; 13, incisor teeth; 14, canine;
  15, 16, 17, premolars; 18, molar. _a_, condyloid canal; _b_,
  hypoglossal canal; _c_, jugular foramen; _d_, internal auditory
  meatus; _e_, appendicular fossa; _f_, tentorium; _g_, dorsum sellæ;
  _h_, sella turcica; _i_, hamular process; _j_, pterygoid process of
  sphenoid; _k_, optic foramen; _l_, presphenoid sinus; _m_, _m′_,
  frontal sinus; _n_, lamina perpendicularis of the ethmoid (broken at
  cranial edge).]

The nasal cavity opens craniad by the large =nares= (Fig. 39, _j_; Fig.
42, _r_), which are bounded by the premaxillary and nasal bones. In the
natural condition this opening is divided by a median cartilage which is
continuous with the lamina perpendicularis (Fig. 43, _n_) of the
ethmoid, thus forming a partition which divides the nasal cavity into
two separate halves. From the floor of the cranial part of the cavity
rises a ridge formed of the nasal crests of the maxillaries and
premaxillaries, and the cranial portion of the vomer. Farther caudad the
vomer spreads out in a horizontal plane and separates from the floor of
the cavity, so that the nasal cavity is thereby divided by a horizontal
partition into dorsal and ventral portions. The ventral portion is
small, forming the inferior meatus of the nose; it ends caudally at the
=choanæ= (posterior nares, Fig. 41, _o_) which lead into the
nasopharynx. That portion of the nasal cavity lying dorsad of the vomer
is almost completely filled by the ethmoid and the conchæ nasales,
superior and inferior. It is bounded caudally by the lamina cribrosa of
the ethmoid (Fig. 42, _o_). The nasal cavity communicates with the
cranial cavity by the foramina for the olfactory fibres in the lamina
cribrosa; with the nasopharynx by the choanæ; with the exterior of the
body by the nares; with the mouth-cavity by the foramina incisiva or
anterior palatine foramina (Fig. 42, _s_); with the orbit by the
sphenopalatine foramen and the nasolachrymal canal. It communicates
directly also with the frontal sinuses (Fig. 43, _m_, _m′_), the
sphenoidal sinuses (Fig. 43, _l_), and with the cells of the labyrinths
of the ethmoid.


JOINTS AND LIGAMENTS OF THE SKULL.

=Sutures of the Skull.=--The bones of the skull join each other by means
of immovable articulations known as sutures. These sutures are
designated by combining the names of the bones between which they are
situated: as, =sphenofrontal= suture (=sutura sphenofrontalis=), between
the sphenoid and frontal; =nasomaxillary= suture (=sutura
nasomaxillaris=), between the nasal and maxillary bones. When a suture
joins the two corresponding bones of opposite sides the prefix =inter=
is used, as the =intermaxillary= suture (=sutura intermaxillaris=)
between the maxillaries. The sutures bounding the parietals have,
however, received special names not derived in this manner. The suture
caudad of the parietals, separating them from the occipital and
interparietal, is known as the =lambdoidal= suture; that between the two
parietals is the =sagittal= suture; that separating the parietals and
squamous portions of the temporals is the =squamous= suture; that
between the parietals and frontals is the =coronal= suture. The suture
separating the two frontals also is known as the =frontal= suture, in
place of interfrontal.

=Articulations of the Mandible.=--In man the two halves of the mandible
are united craniad, so as to form a single bone. In the cat the two
halves are separate, but articulate closely at the =symphysis menti= by
a thin interarticular cartilage.

The articulation of the mandible at the mandibular fossa of the temporal
is covered with a close =articular capsule=. The mandibular fossa is
lined with cartilage. A slender ligament passes from the angular
process of the mandible caudad to the external auditory meatus, being
attached to the latter about 8 millimeters from its medial end. This is
the =stylomandibular ligament=.


V. BONES OF THE THORACIC EXTREMITIES.


=Scapula= (Figs. 44 and 45).--The scapula may be described as a flat
triangular bone with one angle rounded. It lies beneath the muscles on
the lateral face of the thorax near its cranial end. From its lateral
surface there projects a flat ridge (Fig. 44, _g_), the =spine= of the
scapula. The ventral end of the ridge is free as a curved process, the
=acromion= process (Fig. 44, _j_).

  [Illustration: FIG. 44.--SCAPULA, LATERAL SURFACE.

  FIG. 45.--SCAPULA, MEDIAL SURFACE.

  _I_, fossa supraspinata; _II_, fossa infraspinata; _III_, fossa
  subscapularis; _IV_, fossa for teres major. _a_, vertebral border;
  _b_, coracoid border; _c_, glenoid border; _d_, glenoid angle and
  fossa; _e_, coracovertebral angle; _f_, glenovertebral angle; _g_,
  spine; _h_, tuberosity of the spine; _i_, metacromion; _j_, acromion;
  _k_, supraglenoidal tubercle; _l_, incisura scapulæ; _m_, coracoid
  process; _n_, groove indicating portion of spine; _o_, _o′_, ridges
  for attachment of muscle-fibres.]

The ventral angle of the scapula (_d_), the =glenoid= angle (lateral
angle of human anatomy), is much heavier than the others and bears a
concave, pear-shaped articular facet, the =glenoid fossa=, for
articulation with the humerus. The border with which this angle is more
nearly continuous may be called the =glenoid= border (_c_) (axillary
border of human anatomy).

Near the narrower cranial end of the glenoid fossa is a small curved
projection of the bone, the =coracoid= process (Fig. 45, _m_). The
border upon which it lies is the =coracoid border= (_b_) (superior
border of human anatomy). The third border is turned toward the
vertebral column and is the =vertebral border= (_a_).

The angle between the glenoid and vertebral borders is the
=glenovertebral= angle (_f_) (inferior angle of human anatomy), and that
between the coracoid and vertebral borders the =coracovertebral= angle
(_e_) (medial angle of human anatomy).

The medial or costal surface (Fig. 45) is smooth and nearly flat. A
shallow furrow (_n_) marks the position of the spine of the scapula.
Between the furrow and the coracoid border are two oblique parallel
ridges (_o_ and _o′_) for the insertion of muscle-fibres. Near the
glenoid border is a well-marked ridge separating the subscapular fossa
(_III_), comprising the greater part of the medial surface of the
scapula, from the fossa in which the teres major muscle has origin
(_IV_). The surface presents several nutrient foramina usually directed
toward the glenoid angle.

The lateral surface (dorsal surface of human anatomy) (Fig. 44) is
divided by the spine (_g_) into two portions. The portion of the scapula
craniad of the spine and the cranial surface of the spine bound the
=supraspinous= fossa (=fossa supraspinata=) (_I_), while the surface
caudad of the spine and the caudal portion of the spine bound the
=infraspinous= fossa (=fossa infraspinata=) (_II_).

The spine (_g_) begins as a triangular elevated area in the middle of
the vertebral margin and runs toward the glenoid angle. It rises
gradually for about two-fifths of its length and then the margin becomes
broader and the spine remains of the same height to its glenoid end.
There is a rough thickening, the =tuberosity= (_h_) of the spine,
situated on its free border about midway between the tip of the acromion
and the vertebral end of the spine. The spine is inclined toward the
glenoid margin so as to form an angle of about 60 degrees with the
caudal half of the lateral surface.

At the base of the acromion process (_j_) the margin of the spine
presents a flat triangular projection, the =metacromion= (_i_), directed
toward the glenoid border.

The acromion (_j_) continues in the direction of the spine. It is
thicker than the spine, smooth and rounded on both its surfaces and both
its borders, and its apex is connected by fibrous tissue to the
clavicle.

The coracoid border (_b_) presents a slight rounded notch, the =incisura
scapulæ= or suprascapular notch (_l_), just dorsad of the glenoid angle,
and at its ventral end bears the coracoid process (_m_) which is
directed ventromediad.

The glenoid angle (_d_) is the only one requiring special mention.
Between the root of the coracoid process and the glenoid cavity it
presents a tubercle, the =supraglenoidal= or bicipital tubercle (_k_),
for the tendon of origin of the biceps muscle. The glenoid angle is
separated by a contracted neck from the rest of the bone. Between this
angle and the inner margin of the acromion there is left a deep notch,
the =great scapular notch=.

  [Illustration: FIG. 46.--CLAVICLE.

  _a_, medial end; _b_, lateral end.]


=Clavicle.= =Clavicula= (Fig. 46).--The clavicle in the cat is greatly
reduced. It is a slender curved rod of bone imbedded in the muscles of
the shoulder and connected by fibrous tissue to the apex of the acromion
process. The lateral end (_b_) is slightly enlarged.


=Humerus= (Figs. 47 and 48).--The humerus forms the support of the upper
arm and articulates by its proximal end with the scapula at the glenoid
cavity, and by its distal end with the radius and ulna, the bones of the
lower arm. It is a nearly cylindrical bone with enlarged ends, and is so
curved that its dorsal and ventral borders are hooked at the opposite
ends so that it has the form of an Italic _f_.

The proximal end of the bone bears on its dorsomedial portion a
thickening, the =head= of the humerus (_a_), which bears a smooth ovoid
articular facet by which the bone articulates with the glenoid cavity of
the scapula. The head is not separated from the body by a distinct
anatomical =neck= as in the human humerus.

  [Illustration: FIG. 47.--HUMERUS, VENTRAL SIDE.

  FIG. 48.--HUMERUS, MEDIAL SIDE.

  _a_, head; _b_, greater tuberosity; _c_, lesser tuberosity; _d_,
  bicipital groove; _e_, pectoral ridge; _f_, deltoid ridge; _g_, rough
  area for insertion of latissimus dorsi and teres major; _h_, nutrient
  foramen; _i_, capitulum; _j_, trochlea; _l_, coronoid fossa; _m_,
  radial fossa; _n_, medial epicondyle; _o_, lateral epicondyle; _q_,
  supracondyloid foramen.]

Along the lateral border of the proximal end of the shaft is a high
rough ridge semicircular in side view, the =great tuberosity= (_b_). It
gives attachment to muscles and is marked on its dorsal border by a deep
depression for the tendon of the infraspinatus muscle. On the medial
margin of the proximal end closely associated with the head is a smaller
elevation, the =lesser tuberosity= (_c_), also for muscular attachment.

Between the greater and lesser tuberosities on the ventral surface is
seen a broad groove, the =sulcus intertubercularis= or =bicipital
groove= (_d_), which passes distad onto the surface of the shaft. In the
natural state it is converted into a canal by overlying tendons and
lodges the tendon of the biceps muscle.

The shaft is nearly cylindrical at its middle, but its dorsoventral
diameter is slightly greater than its mediolateral diameter. Its
proximal end is flattened mediolaterad, while its distal end is
flattened dorsoventrad.

From the ventral margin of the greater tuberosity a ridge, the
=pectoral= ridge (_e_), is continued onto the surface of the shaft, and
from the dorsal margin another ridge, the =deltoid= ridge (_f_), passes
distad and ventrad so as to meet the pectoral ridge near the middle of
the ventral surface of the bone. On the medial margin of the bone near
the junction of the first and second fourths is a roughened area (_g_)
for the attachment of the tendons of the latissimus dorsi and teres
major muscles, and on the same surface near the junction of the second
and last thirds is a nutrient foramen (_h_).

The distal end of the bone presents a smooth saddle-shaped articular
surface, which, in well-marked bones, is divided, when seen from the
ventral surface, by a slight nearly median ridge into two unequal
portions, lateral and medial (_i_ and _j_). The lateral half is rounded
and is called the =capitulum= (_i_). It is broader ventrad than dorsad,
and is not continued onto the dorsal surface of the bone. It is for
articulation with the proximal end of the radius.

The medial half of the surface, the =trochlea= (_j_), is concave and
passes directly into the capitular surface laterad, but is limited
mediad by a sharp ridge. It is continued onto the dorsal surface of the
bone, where it is limited also laterad by a ridge. It articulates with
the semilunar notch of the ulna.

Proximad of the trochlea the dorsal surface presents a deep fossa, the
=olecranon fossa=, which receives the olecranon of the ulna when the arm
is straightened. On the ventral surface (Fig. 47) are two shallower
fossæ separated by a longitudinal ridge. The one over the trochlea
receives the coronoid process of the ulna when the arm is bent, and is
called thence the =coronoid fossa= (_l_). The one over the capitulum,
the =radial fossa= (_m_), receives a triangular facet on the proximal
end of the radius at the same time. Between the radial and coronoid
fossæ on one side and the olecranon fossa on the other is only a thin
plate of bone. On the medial surface of the distal end is a considerable
roughened elevation, the =medial epicondyle= (_n_) (epitrochlea). It
gives origin to flexor muscles and to the ulnar collateral ligaments of
the elbow-joint. Opposite the medial epicondyle over the capitulum is
the =lateral epicondyle= (_o_) for the origin of extensor muscles of the
forearm and of the radial collateral ligaments of the elbow-joint. From
the lateral epicondyle a ridge, the lateral =supracondyloid ridge=
(_p_), continues proximad, curving onto the dorsal surface of the bone
and ending about opposite the junction of the deltoid and pectoral
ridges.

Proximad of the medial epicondyle the bone is pierced near its medial
margin by an oblique oval foramen, the =supracondyloid foramen= (_q_).


=Radius= (_I_, Figs. 49 and 50).--In the usual position the radius lies
with its proximal end on the lateral side of the arm, articulating with
the capitulum of the humerus. The proximal end is thus laterad of the
proximal end of the ulna. Its distal end, however, lies on the medial
side of the distal end of the ulna, so that the radius in the natural
position crosses ventrad of the ulna.

The radius is a curved bone slightly flattened dorsoventrally, with
enlarged ends. It may be described as consisting of a shaft and of a
proximal and a distal end. Its proximal end presents on the ventral
surface a tuberosity, the =bicipital tuberosity= (_c_), for the
insertion of the tendon of the biceps muscle. Proximad of this the bone
is contracted to form a =neck= (_b_) which is surmounted by a =head=
(_a_). The head has on its proximal surface a depressed oval facet by
which it articulates with the capitulum, and on its ulnar border a long
narrow facet, the =articular circumference= (_d_), for articulation with
the radial notch of the ulna; also a triangular facet (_e_), which fits
into the radial fossa of the humerus.

The shaft is convex dorsad and concave ventrad. The distal end is
somewhat pyramidal. From its medial or radial side a wedge-shaped
process, the =styloid= process (_f_), extends distad. The distal
surface of the end together with the lateral surface of the styloid
process form a concave articular cavity (_g_) which fits against the
scapholunar bone.

  [Illustration: FIG. 49.--RADIUS AND ULNA, DORSOLATERAL VIEW.

  FIG. 50.--RADIUS AND ULNA, VENTROMEDIAL VIEW.

  _I_, radius; _II_, ulna. _a_, head of radius; _b_, neck; _c_,
  bicipital tuberosity; _d_, articular circumference; _e_, facet for
  radial fossa of humerus; _f_, styloid process of radius; _g_, facet
  for articulation of scapholunar bone; _h_, semilunar (or great
  sigmoid) notch of ulna; _i_, coronoid process; _j_, olecranon; _k_,
  area for insertion of brachialis and clavobrachial muscles; _l_, rough
  area for attachment of interosseous membrane; _m_, styloid process of
  ulna.]

The dorsal surface of the distal end is marked by longitudinal grooves
for tendons, and its lateral or ulnar surface bears a concave facet for
articulation with the ulna.


=Ulna= (_II_, Figs. 49 and 50).--The ulna is a long slender bone,
flattened mediolaterad. It is enlarged at its proximal end and becomes
gradually smaller toward the distal end.

The proximal end is marked ventrally by a deep excavation, the
=semilunar notch=, or =great sigmoid cavity= (_h_). By the saddle-shaped
articular surface of the semilunar notch it articulates with the
trochlea. This articular surface is divided into two parts by a
transverse non-articular area. The distal boundary of the semilunar
notch is a blunt process, the =coronoid= process (_i_), which bears on
its lateral surface a concave facet, the =radial notch=, for the head of
the radius.

The portion of the bone proximad of the semilunar notch is called the
=olecranon= (_j_). It fits into the olecranon fossa of the humerus when
the arm is straightened, and is rough at its end for the insertion of
tendons.

The body of the ulna becomes triangular distad. The distal end is
slightly larger than the shaft just proximad of it, and bears on its
radioventral side a hemispherical head for articulation with the radius.
Distad of the head the bone continues as the flattened =styloid= process
(_m_), which projects distad from its dorsolateral side and is smooth on
the medial side of its apex, for articulation with the cuneiform bone of
the wrist.


=Carpus= (Fig. 51).--The carpus (wrist) consists of seven bones arranged
in two rows, three in the proximal row and four in the distal row.
Beginning on the medial side of the hand (thumb or radial side), the
first bone in the proximal row is the =scapholunar= (_a_) (equal to the
scaphoid or navicular and lunar of the human hand). It articulates with
the radius. The next is the =cuneiform= (_b_), articulating with the
styloid process of the ulna, and the next, which is attached to the
cuneiform and projects freely ventrad, is the =pisiform= (_c_).

In the distal row the bone on the radial side is the =trapezium= (_d_);
the next is the trapezoid (_e_), the next the os magnum (_f_), and the
last the unciform (_g_). The distal row articulates with the metacarpals
or bones of the palm of the hand (1-5).

In the kitten the scapholunar is represented by three bones, the
=scaphoid= or navicular, on the radial side, the =lunare=, between the
scaphoid and the cuneiform, and a =centrale=, which lies distad of the
other two.

_Scapholunar Bone._ _Os scapholunaris_ (Fig. 51, _a_).--The scapholunar
is a quadrangular bone with the ventroradial angle produced into a blunt
process. Its proximal surface is smooth and articulates with the distal
end of the radius. The distal end is marked by oblique ridges and
articulates with the unciform, os magnum, trapezoid, and trapezium. The
ulnar surface articulates with the cuneiform, and the dorsal surface of
the ventroradial process with the radial sesamoid.

_Cuneiform Bone._ (_Os triquetrum BNA_) (Fig. 51, _b_).--The cuneiform
bone has the form of a flattened pyramid. Its base articulates with the
unciform, its proximoulnar surface with the pisiform except at its
dorsal margin, where it articulates with the styloid process of the
ulna. On its proximoradial surface is a smooth facet for articulation
with the scapholunar.

_Pisiform Bone._ _Os pisiforme_ (Fig. 51, _c_).--The pisiform bone is
about twice as long as broad, with enlarged ends. Its dorsal end
articulates with the cuneiform, and on its proximal surface, separated
from the above by a smooth ridge, is a smooth facet for articulation
with the styloid process of the ulna.

  [Illustration: FIG. 51.--CARPUS, METACARPUS, AND PHALANGES, DORSAL
  SURFACE.

  _a_, scapholunar bone; _b_, cuneiform; _c_, pisiform; _d_, trapezium;
  _e_, trapezoid; _f_, os magnum; _g_, unciform; _h_, radial sesamoid;
  _i_, proximal phalanges; _j_, second phalanges; _k_, distal
  phalanges; 1, 2, 3, 4, 5, metacarpals in order from the radial side.]

_Unciform Bone._ (_Os hamatum BNA_) (Fig. 51, _g_).--The unciform is a
wedge-shaped bone with the apex of the wedge directed proximad, and
smooth for articulation with the scapholunar. By a part of its ulnar
surface it articulates with the cuneiform, and by its radial surface
with the os magnum. Its distal end articulates with the fourth and fifth
metacarpals.

_Os magnum._ (_Os capitatum BNA_) (Fig. 51, _f_).--The os magnum may be
described as an oblong plate bearing on its proximal surface a
semicircular ridge which crosses it diagonally. The proximal end of the
bone articulates with the scapholunar. Its distal end articulates with
the third metacarpal except near its ventroulnar angle, where it
articulates with the fourth metacarpal. Its ulnar surface articulates
with the unciform. Its radial border articulates with the trapezoid, the
third metacarpal, and, by two facets, with the second metacarpal.

_Trapezoid._ (_Os multangulum minus BNA._) (Fig. 51, _e_).--The
trapezoid is somewhat wedge-shaped, with the apex of the wedge pointing
ventrad. Its proximal side articulates with the scapholunar, its distal
side with the second metacarpal, its ulnar side with the os magnum, and
its radial side with the trapezium.

_Trapezium._ (_Os multangulum majus BNA._) (Fig. 51, _d_).--The
trapezium has the form of a triangular prism curved into a semicircle.
The convex face looks proximad and articulates by its ventral half with
the scapholunar. The ulnar surface articulates with the second
metacarpal dorsally, and ventrally with the trapezoid. Its radial
surface articulates with the first metacarpal.


=Bones of the Hand or Manus= (Fig. 51, 1-5).--The _Metacarpals_.
_Metacarpus._--The metacarpals are the five bones of the palm of the
hand; they are numbered from one to five, beginning with the thumb. They
are cylindrical elongated bones with enlarged ends. The distal end is
called the head, and the proximal end the base. Each head bears a
hemispherical articular facet which is marked over its ventral half by a
prominent smooth ridge. The surface dorsad of the ridge articulates with
the proximal head of a phalanx. The ridge and the surface at its sides
are for a pair of sesamoid bones.

The first metacarpal (1) is the shortest. Its head is oblique, and it
articulates by the ulnar half of its proximal surface with the trapezium
(_d_); by the radial half with the radial sesamoid (_h_).

The second metacarpal (2) is marked on the proximal part of its dorsal
surface by an oblique groove passing from the radial side distad to the
ulnar side. The base articulates with the trapezoid (_e_). The ulnar
surface of the proximal end articulates with the os magnum (_f_) and
third metacarpal, while the radial surface articulates with the
trapezium (_d_).

The third metacarpal (3) is the longest, and its base is rhomboidal with
a projecting dorsoradial angle separated by a groove from the rhomboid
surface. The proximal end articulates with the os magnum (_f_) and
second metacarpal; the radial surface of the proximal end with the
second, and the ulnar surface with the fourth, metacarpal.

The fourth metacarpal (4) has a base similar in form to that of the
third, and when placed in position with the fifth the two form a
hemispherical facet which articulates with the unciform (_g_) and os
magnum (_f_). The fourth metacarpal articulates by its radial side with
the third, and by its ulnar side with the fifth.

The fifth metacarpal (5) articulates by its proximal end with the
unciform (_g_), and by the radial side of its proximal end with the
fourth metacarpal.

_Digits_ (Fig. 51).--The first digit of the hand is called the =pollex=
(thumb), the second the =index=, the third the =medius=, the fourth the
=annularis=, the fifth the =minimus=.

The first digit has two phalanges, each of the others three phalanges.

_Phalanges_ (Fig. 51, _i_, _j_, _k_).--The phalanges of the proximal row
(_i_) are elongated, flattened dorsoventrally and curved so as to be
longitudinally convex dorsad. All have thickened ends. The proximal end
is notched, and its proximal surface looks dorsad and is concave for the
head of the metacarpal. The distal end is pulley-shaped, and the pulley
surface extends farther on to the ventral than on to the dorsal surface,
and serves for articulation with the middle phalanx.

The phalanges of the middle row (_j_) are like those of the proximal
row, but shorter. The proximal surface is triangular and marked by a
median facetted ridge. The whole surface is smooth and adapted to the
distal end of the phalanx of the first row. The distal end is
transversely elongated, so as to be cylindrical, and projects more
toward the ulnar than toward the radial side. The distal phalanx (_k_)
articulates with this cylinder so that when it is fully extended it lies
on the ulnar side of the middle phalanx.

The distal phalanx (_k_) has the form of a quadrangular prism. It is
excavated on its proximal surface for articulation with the middle
phalanx. Its distal surface presents dorsad a deep excavation from the
bottom of which arises a compressed plate of bone having the form of a
bird’s beak. The depression receives the base of a claw, and the
beak-like projection supports the claw.

_Sesamoid Bones of the Hand._ _Ossa sesamoidea._--The hand contains, in
addition to those already described, eleven small bones that are
developed in tendons.

One of these, the =radial= sesamoid (Fig. 51, _h_), is closely applied
to the radial end of the scapholunar bone. It is developed in the
tendon of the extensor brevis pollicis muscle.

The other ten occur in pairs as small flattened curved bones on the
ventral side of the joint between each metacarpal and the phalanx with
which it articulates.


JOINTS AND LIGAMENTS OF THE THORACIC LIMBS.

The =shoulder-joint= is an arthrodial or ball-and-socket joint. The
bones entering into its formation are the scapula and the humerus.

The =capsular ligament= or =articular capsule= is very ample and allows
for extended movement of the humerus. It is attached to the edge of the
glenoid fossa of the scapula and passing distad covers the head of the
humerus and is inserted at the line of junction of the shaft and the
epiphysis which forms the head of the bone. On the lateral side of the
ventral surface of the humerus the attachment continues distad about two
centimeters along the lateral edge of the bicipital groove. On the
medial side the insertion passes over the proximal end of the lesser
tuberosity. A strong transverse band passes from the greater tuberosity
to the lesser tuberosity and bridges the bicipital groove, converting it
into a canal. The lateral and medial parts of the capsule are
strengthened by thicker bands of fibres, the more prominent medial one
of which passes from the coracoid process of the scapula to the lesser
tuberosity. To the capsule are closely united parts of the
supraspinatus, infraspinatus, coracobrachialis, and subscapularis
muscles. A synovial membrane lines the capsule within and forms a sheath
around the biceps tendon, so that the latter does not actually enter the
synovial capsule.

The =elbow-joint= (Figs. 52 and 53) is a ginglymus or hinge-joint. The
bones which enter into it are the humerus, radius, and ulna.

The capsule of the joint forms a sac, with the following attachments to
the bones: (1) To the humerus it is attached at the proximal edge of the
coronoid and radial fossæ; to the sides of the capitulum and trochlea
distad of the two epicondyles, and to the distal edge of the olecranon
fossa. (2) To the ulna it is attached at the edges of the radial and
semilunar notches; (3) to the radius around the articular facet, two or
three centimeters distad of the border. Many of the muscles of this
region are closely attached to the capsule.

  [Illustration: FIG. 52.--LIGAMENTS OF ELBOW-JOINT, MEDIAL SIDE.

  FIG. 53.--ELBOW-JOINT, LATERAL VIEW.

  Fig. 52.--1, humerus; 2, ulna; 3, radius. _a_ and _b_, the two medial
  collateral ligaments.

  Fig. 53.--1, humerus; 2, radius; 3, ulna. _a_, dorsal collateral
  ligament; _b_, ventral collateral ligament; _c_, annular ligament.]

Closely connected with the capsule of the joint are the =collateral
ligaments=. The two =medial= collateral ligaments (Fig. 52) arise from
the medial epicondyle. One (_b_) passes distad and laterad to the
interval between the radius and ulna; here it divides, one branch going
to the head of the radius, while the other is attached to the lateral
surface of the ulna at the edge of the semilunar notch. The second
medial ligament (_a_) lies dorsad of the first; it passes to the medial
surface of the ulna, at the distal edge of the semilunar notch.

The two collateral ligaments on the =lateral= side (Fig. 53) arise from
the lateral epicondyle. The ventral one (_b_) passes almost directly
distad and is inserted into the lateral surface of the proximal end of
the radius about one centimeter from the articular surface; its inner
surface is partly united to the annular ligament (_c_) of the radius.
The dorsal one (_a_) is attached to the lateral border of the semilunar
notch of the ulna.

=Articulations of Radius and Ulna.=--The proximal =radio-ulnar
articulation= (Fig. 53) is by a pivot-joint or trochoid. The two bones
are held in place by the =annular= ligament (Fig. 53, _c_). This is
attached on the lateral side to the dorsal border of the radial notch of
the ulna, passes around the head of the radius, receiving some
ligamentous fibres which come from the lateral epicondyle, and is
attached to the coronoid process of the ulna. The annular ligament is
closely united with the capsule of the joint.

The radius and ulna are united for about their middle third by the thin
=interosseous membrane=, which fills the interosseous space between
their adjacent edges.

=The Wrist.=--At the wrist or carpus there are in reality three joints,
the first between the radius and ulna proximad and the first row of
carpals distad, the second between the two rows of carpal bones, the
third between the distal row of carpals and the metacarpals. The first
two are movable joints; the third is not. Each of these three joints has
a capsule, and the bones entering into the joints are interconnected by
numerous ligaments. These ligaments are named by combining the names of
the two bones which they interconnect. Ligaments which interconnect
bones of the same row in the carpus are sometimes distinguished as
=interosseous= ligaments, as contrasted with =intercarpal= ligaments,
which connect together bones of different rows. According to their
position the ligaments may also be distinguished as dorsal, ventral, and
lateral. Detailed descriptions and figures of all these ligaments are
given by Strauss-Durckheim.

=Metacarpals.=--The joint between the carpals and metacarpals has been
described. At the distal end of the metacarpals the articulations with
the phalanges have each a capsule. The joint is further strengthened by
a double lateral ligament on each side. The two sesamoid bones at each
joint are interconnected by a strong transverse ligament, and each is
connected with the head of the metacarpal and the base of the first
phalanx by a lateral ligament.

=Phalanges.=--Between the phalanges the joints possess capsules, and
each has a radial and an ulnar lateral ligament.


VI. BONES OF THE PELVIC EXTREMITIES.


=Innominate Bones. Ossa innominata.= (=Os coxæ BNA=) (Figs. 54 and
55).--The two innominate bones articulate with the sacrum and extend
thence caudoventrad and finally turn mediad and unite in the middle
line, forming the =symphysis pubis=. They thus form an arch, =the pelvic
arch=, =pelvic girdle= or =pelvis=, which is closed dorsad by the
sacrum.

In the middle of the lateral surface of each bone is a hemispherical
depression, the =acetabulum= (Fig. 55, _d_), which receives the head of
the femur.

  [Illustration: FIG. 54.--INNOMINATE BONE OF KITTEN, VENTROLATERAL
  VIEW.

  _I_, ilium; _II_, ischium; _III_, pubis; _IV_, acetabular bone. _a_,
  acetabulum; _b_, obturator foramen.]

In the kitten each innominate bone is composed of three principal parts
united by sutures (Fig. 54). From the sacrum to the acetabulum is a
single bar, the =ilium= (_I_). Caudad of the acetabulum are two bars.
The dorsal one of these is the =ischium= (_II_), and the ventral one is
the =pubis= (_III_). The ischium enters into the formation of the
acetabulum (_a_), but the pubis does not. The two bones, however, are in
contact at the ventral edge of the acetabulum. From this point they
diverge, but unite with one another again near the middle line and thus
enclose an oval foramen, the =obturator foramen= (_b_). Wedged between
the ilium, ischium, and pubis at their point of junction and helping to
form the acetabulum is a small irregular bone, the =acetabular bone=
(_IV_). In the adult cat these four parts are united into a single bone
which is nevertheless usually described, ignoring the acetabular piece,
as made up of ilium (Fig. 55, _I_), ischium (_II_), and pubis (_III_).

  [Illustration: FIG. 55.--INNOMINATE BONE OF ADULT CAT, VENTROLATERAL
  VIEW.

  _I_, ilium; _II_, ischium; _III_, pubis. _a_, crest of the ilium; _b_,
  posterior inferior spine; _c_, great sciatic notch; _d_, acetabulum;
  _d′_, incisura acetabuli; _e_, spine of the ischium; _f_, lesser
  sciatic notch; _g_, tuberosity of the ischium; _h_, ramus of the
  ischium; _i_, ramus of the pubis; _j_, obturator foramen; _k_, pubic
  tubercle; _l_, iliopectineal line; _l′_, ilio-pectineal eminence; _m_,
  anterior superior process.]

The =ilium= (_I_) is somewhat contracted at the middle and broader at
its ends. One end enters into the acetabulum (Fig. 55, _d_) and forms
about one-fifth the articular surface. This end is also the thickest
part of the bone. The lateral surface of the ilium is concave for the
attachment of muscles. The medial surface is smooth over its acetabular
half and rough over its sacral half. The rough portion is marked at its
junction with the smooth portion by the ear-shaped =auricular
impression= by which the bone articulates directly with the sacrum. The
caudal half of that part of the medial surface craniad of the auricular
impression gives attachment to the ilio-sacral ligaments which bind the
ilium to the sacrum. The dorsal border is straight at its cranial end
and concave and rounded at its caudal end. Between the two portions and
at the dorsal edge of the auricular surface is a protuberance
corresponding to the =posterior inferior spine= (Fig. 55, _b_) of the
human ilium. The concavity of the dorsal border (_c_) corresponds to the
great sciatic notch of the human ilium. At its caudal end is the short
=spine of the ischium= (_e_), which is not a part of the ilium. The
ventral border of the ilium is broad caudad, becoming narrower craniad.
The lateral margin of the ventral border is continued to a tuberosity at
the edge of the acetabulum; its medial margin is called the
=iliopectineal line= (_l_) and extends on the pubis to the symphysis. An
eminence, the =iliopectineal eminence= (_l′_), on the iliopectineal
line, lies opposite to the acetabulum at about the junction of the ilium
and pubis. The cranial end of the bone is thickened, forming the =crest=
(_a_) of the ilium. At the junction of the crest with the ventral border
is a projection, the =anterior superior process= (_m_) of human anatomy.

The =pubis= (_III_) (including the acetabular bone) enters into the
formation of the acetabulum (_d_) constituting about one-sixth the
circumference, but less than one-sixth its area. It may be described as
a flat, curved bone, contracted at the middle and expanded at the ends.
The dorsal end enters into the acetabulum; the ventral end unites with
the opposite bone at the symphysis pubis and sends caudad a projection,
the =ramus= (_i_) of the pubis, which unites with the ramus of the
opposite bone to form about two-thirds of the entire symphysis. At the
sides of the symphysis a slightly marked angle projects craniad from
each of the pubic bones; these two together constitute the =pubic
tubercle= (_k_), for the origin of the rectus abdominis muscle. The
surfaces of the ramus are smooth. One of its borders is concave and
enters into the formation of the obturator foramen (_j_). Another of its
borders is the iliopectineal line (_l_). Its third border is rough for
the symphysis.

The =ischium= (_II_) has the form of a triangular prism contracted at
the middle. Its cranial end forms nearly two-thirds of the acetabulum.
Its caudal end bears dorsad a rough thickening, the =tuberosity= of the
ischium (_g_). From the caudal half of the ventral border of the bone a
sickle-shaped process, the =ramus= (_h_) of the ischium, curves
medioventrad and then craniad and joins the ramus of the pubis. Its
medial border is rough and enters into the symphysis, forming the caudal
one-third. The lateral angle of the bone is rounded. Its dorsal angle is
marked near the cranial end by the =spine= (_e_) of the ischium. The
concavity between this spine and the tuberosity corresponds to the
=lesser sciatic notch= (_f_) of human anatomy.

The acetabulum (_d_) is cup-shaped. The ventral one-sixth of its border
is deficient and a broad groove extends from the deficiency to the
bottom of the cup. The deficiency, =incisura acetabuli=, or =acetabular
notch= (_d′_), is closed naturally by a ligament, and the groove gives
origin to the ligament (ligamentum teres) which attaches the head of the
femur.

  [Illustration: FIG. 56.--LEFT FEMUR, VENTRAL SIDE.

  _a_, head; _b_, neck; _c_, depression for round ligament; _d_, great
  trochanter; _e_, trochanteric fossa; _f_, intertrochanteric line; _g_,
  lesser trochanter; _h_, linea aspera; _i_, medial condyle; _j_,
  lateral condyle; _k_, intercondyloid fossa; _l_, lateral epicondyle.]


=Femur= (Fig. 56).--The femur is the proximal bone of the posterior
extremity. It consists of enlarged proximal and distal ends connected by
a nearly cylindrical shaft. The proximal end presents on its medial side
a hemispherical =head= (_a_) which fits into the acetabulum. It is
supported by a =neck= (_b_) which is contracted near the head and
expanded dorsoventrally where it joins the remainder of the bone. The
medial surface of the head presents near its ventral border a depression
(_c_) for the insertion of the round ligament of the femur. Ventrad the
articular surface of the head extends as an acute projection onto the
shaft, so that the whole articular surface appears somewhat pear-shaped.
On the lateral side of the proximal end opposite the head is a
projecting mass, the =great trochanter= (_d_), forming the end of the
shaft. On the medial side of the great trochanter at its junction with
the neck is a deep fossa, the =trochanteric= fossa or =digital= fossa
(_e_) for the insertion of muscles. From the ventral surface of the
great trochanter a ridge, the =intertrochanteric= line (_f_), is
continued distad, ending in a pyramidal projection, the =lesser
trochanter= (_g_), which serves for the insertion of muscles. A second
ridge is continued to the lesser trochanter from the neck. A slight but
well-marked ridge, the =spiral= ridge or line, runs round two sides of
the neck parallel to the second ridge.

The shaft is nearly straight and cylindrical. A rough line is continued
along its ventral surface from the lesser trochanter, and a similar line
along its lateral surface from the greater trochanter; these unite
ventrad to form the =linea aspera= (_h_). On its ventral surface is a
nutrient foramen, directed proximad.

The shaft gradually widens distad and ends in two =condyles= (_i_ and
_j_) which are continuous dorsad but separated ventrad by a deep notch,
the =intercondyloid fossa= (_k_). The distal surface of the shaft and
condyles is articular. This articular surface is larger on the lateral
condyle (_j_). The part of the articular surface on the end of the shaft
(=patellar surface=) is for the patella; that part of it on the condyles
and separated by the notch is for the tibia.

On the lateral surface of the lateral condyle is a slight prominence,
the lateral epicondyle (_l_), and on the medial surface of the medial
condyle is another prominence, the medial epicondyle; both are for the
attachment of ligaments.


=Patella= (Fig. 1, _r_).--The patella is a small flat bone with a
pear-shaped outline, having its apex distad. It lies against the
articular surface at the lower end of the shaft of the femur. It thus
covers the knee-joint. The inner surface is smooth and convex from side
to side, but concave in a proximodistal line. It fits against the lower
end of the femur. Its outer surface is rough and concave. It is a
sesamoid bone inserted in the tendon of the quadriceps femoris muscle.

Three other sesamoid bones are found in the region of the knee (see Fig.
61, p. 89). Two are in the tendons of the gastrocnemius muscle, proximad
of the two condyles of the femur. The third is in the tendon of the
popliteus muscle, just laterad of the lateral condyle of the femur.

  [Illustration: FIG. 57.--TIBIA AND FIBULA OF LEFT LEG, DORSAL VIEW.

  _I_, tibia; _II_, fibula. _a_, medial condyle of the tibia; _b_,
  lateral condyle; _c_, spine of the tibia; _d_, crest of the tibia;
  _e_, tubercle for attachment of the patellar ligament; _f_, medial
  malleolus; _g_, projection of dorsal surface of the tibia; _h_, head
  of fibula; _i_, lateral malleolus.]


=Tibia= (_I_, Fig. 57).--The tibia is the longer of the two bones of the
leg between the knee and the ankle, and is the longest bone of the body.
It has a triangular shaft and enlarged proximal and distal ends.

The proximal end is curved ventrad and projects into two prominences,
the =tuberosities=, on either side. Each tuberosity bears on its
proximal end an articular facet for the condyles of the femur; these are
known respectively as the =lateral= and =medial condyles= (_a_ and _b_)
of the tibia. The condyles are oval, convex dorsoventrad, and concave
from side to side. The two condyles are separated at the middle of their
contiguous margins by a bicuspid projection, the =spine= of the tibia
(_c_). They are continuous dorsad, but separated ventrad by a deep notch
between the tuberosities, the =popliteal= notch. On the distal side of
the lateral condyle is an elongated facet for the proximal end of the
fibula.

The shaft is triangular, smallest at about its middle and enlarged at
both ends. It presents dorsal, medial, and lateral borders, and medial,
lateral, and ventral surfaces. The lateral surface is concave proximad.
The medial surface is convex. The two are continuous at the distal end.
At their proximal ends the border separating them is raised into a
prominent ridge, the =crest= (_d_) of the tibia, the proximal end of
which contributes to increase the proximal surface of the bone, and
presents an oblong tubercle (_e_) for the insertion of the =ligamentum
patellæ= (ligament of the quadriceps femoris muscle). The ventral
surface is concave proximad where it abuts upon the tuberosities. Its
proximal half is crossed by two rough parallel lines, the distal one of
which crosses in a spiral course from the lateral to the medial border;
near its beginning is a nutrient foramen.

The distal end extends farther distad on its medial side. The extension
is the =medial malleolus= (_f_). The malleolus presents two grooves on
its medial surface for the tendons of muscles. On the lateral side of
the distal end is an oblique triangular facet for the distal end of the
fibula. The ventral surface of the distal end presents an oblique border
which passes from the apex of the malleolus proximolaterad. The dorsal
surface extends into a V-shaped projection (_g_) between the malleolus
and the fibular facet. The distal end presents an oblique ridge running
from the apex of the V-shaped extension of the dorsal surface to near
the base of the medial malleolus. The ridge and the concavities on
either side of it, the medial one of which is deeper, fit against the
proximal trochlear surface of the astragalus.


=Fibula= (_II_, Fig. 57).--The fibula lies at the lateral side of the
tibia in the shank. It is a slender triangular bone with enlarged
proximal and distal ends.

The proximal end or head (_h_) is flattened. It bears a facet on its
proximomedial surface for articulation with the tibia, and is
longitudinally grooved on the outer surface.

The shaft has a very sharp medial border. This border is turned toward
the tibia and gives attachment to the interosseous membrane, which runs
between the tibia and fibula.

The distal end is expanded to form the =lateral malleolus= (_i_). This
bears a facet on the proximal portion of its medial surface near its
dorsal margin, for the tibia, and distad of this is a second facet for
the astragalus. The ventral and lateral surfaces are grooved for
tendons.


=Tarsus= (Fig. 58).--The tarsus consists of seven bones. The longest of
these, lying on the lateral side of the foot and forming the support of
the heel, is the =calcaneus= or =os calcis= (_a_). It articulates distad
with a bone, the =cuboid= (_c_), which bears the fourth and fifth
metatarsals. Lying between the calcaneus and the tibia is the
=astragalus= or =talus= (_b_), the distal end of which articulates with
the boat-shaped =navicular= or =scaphoid= (_d_). The scaphoid bears on
its distal surface the three cuneiform bones, lateral (_e_), medial
(_g_), and intermediate, bearing the rudiment of the first metatarsal
and the second and third metatarsals.

_Astragalus._ (_Talus BNA_) (Fig. 58, _b_).--The astragalus may be
divided into body, neck, and head. The body is marked on its proximal
surface by a deep pulley-like groove for the articulation with the
distal end of the tibia, and on its lateral and medial surfaces by
curved facets for articulation with the malleoli of the tibia and
fibula. This entire surface for articulation with the bones of the leg
is known as the trochlea. The lower surface is marked by two facets
separated by a groove; these are for articulation with corresponding
facets on the calcaneus. Distally the bone contracts to form the =neck=
and enlarges at the end, forming the =head=, which is smooth on its
distal surface for articulation with the navicular or scaphoid.

_Calcaneus_ (Fig. 58, _a_, and Fig. 59).--The calcaneus (os calcis) is
the largest bone of the foot and forms the heel. It is two or three
times as long as broad and has six surfaces: dorsal, ventral, medial,
lateral, proximal, and distal. The proximal one-half of the dorsal
surface (Fig. 59) is smooth, while the distal half is broadened and
bears two facets which are separated by a groove. These articulate with
the corresponding facets on the astragalus. The medial facet is borne on
a projection of the bone, the sustentaculum tali (_c_). Distad of the
facets the surface is rough. The ventral surface is smooth. The proximal
end (_b_) is grooved for the tendon of Achilles. The lateral surface is
smooth and marked by a grooved tubercle, the =peroneal tubercle= (_d_),
near the distal end. The medial surface is marked by part of the
articular facet for the astragalus, and also by the grooved
sustentaculum tali. The distal end (_a_) articulates with the cuboid.

  [Illustration: FIG. 58.--TARSUS, METATARSUS, AND PHALANGES OF LEFT
  FOOT, VENTRAL VIEW.

  _a_, calcaneus; _b_, astragalus; _c_, cuboid; _d_, scaphoid; _e_,
  lateral cuneiform; _g_, medial cuneiform; _h_, peroneal groove, for
  the tendon of the peroneus longus muscle; _i_, proximal phalanges;
  _j_, second row of phalanges; _k_, distal phalanges; _l_, sesamoid
  bones. 1, rudimentary first (medial) metatarsal; 2, 3, 4, 5, the other
  metatarsals.]

  [Illustration: FIG. 59.--CALCANEUS OF RIGHT FOOT, DORSAL VIEW.

  _a_, distal facet for cuboid; _b_, proximal end with groove for tendon
  of Achilles; _c_, sustentaculum tali; _d_, peroneal tubercle.]

_Cuboid._ _Os cuboideum_ (Fig. 58, _c_).--The cuboid has somewhat the
form of a cube and articulates by its proximal end with the calcaneus
(_a_), and by its distal end with the fourth and fifth metatarsals. Its
medial surface articulates with the scaphoid (_d_) and lateral cuneiform
(_e_). The ventral surface is marked near its distal end by an oblique
ridge, distad of which is a deep groove, the peroneal groove (_h_), for
the tendon of the peroneus longus muscle.

_Scaphoid._ (_Os naviculare pedis BNA_) (Fig. 58, _d_).--The scaphoid is
a boat-shaped bone. Its proximal surface is marked by a concave facet
for the head of the astragalus (_b_), and its distal surface has three
facets for the lateral (_e_), intermediate and medial (_g_) cuneiform
bones. At the junction of the ventral with the medial surface is a
prominent tubercle. The lateral surface bears two linear facets for
articulation with the calcaneus (_a_) and cuboid (_c_).

_Lateral Cuneiform._ _Ectocuneiform._ _Os cuneiforme tertium BNA_ (Fig.
58, _e_).--The lateral cuneiform is a wedge-shaped bone with a hooked
process extending from the ventral sharp angle of the bone. It
articulates by its proximal end with the scaphoid (_d_), and by its
distal end with the third metatarsal. The medial surface bears near its
distal end two facets for the second metatarsal, and on its proximal end
a facet for the intermediate cuneiform. The caudal surface has a facet
on its proximal end for the cuboid (_c_).

_Intermediate Cuneiform._ _Mesocuneiform._ _Os cuneiforme secundum
BNA._--The intermediate cuneiform is small and wedge-shaped, with the
base of the wedge dorsad. It lies between the lateral cuneiform and the
medial cuneiform, articulates by its proximal end with the middle facet
of the scaphoid, and bears on its distal end the second metatarsal. It
is not visible in ventral view.

_Medial Cuneiform._ _Entocuneiform._ _Os cuneiforme primum BNA_ (Fig.
58, _g_).--The medial cuneiform lies on the medial side of the foot. It
is a flat triangular bone about twice as long as broad, and broader at
its proximal end than at the distal end. It bears on its distal end the
rudimentary first metatarsal. The proximal end is oblique and bears a
concave facet for the lateral distal facet of the scaphoid (_d_). The
lateral surface has a concave facet at its proximal end for the
intermediate cuneiform, while the distal portion is applied against the
medial surface of the second metatarsal.


=Bones of the Foot or Pes= (Fig. 58).--_Metatarsals._ _Metatarsus_ (Fig.
58, 1-5).--The metatarsals are five in number. They bear a close
resemblance to the metacarpals, but they may be distinguished by their
bases.

The _first_ metacarpal (1) is rudimentary and conical. Its base has a
facet for the distal end of the medial cuneiform (_g_), while the outer
surface fits into a depression on the inner surface of the base of the
second metatarsal.

The _second_ (2). The proximal surface of the base is triangular,
corresponding to the distal end of the intermediate cuneiform. The
medial surface is marked by two concavities, one along the proximal
border for the distal end of the medial cuneiform, and one distad of
this for the first metatarsal. The lateral surface bears on the
proximal margin an oblique triangular facet dorsad and a similar facet
ventrad, both for the lateral cuneiform (_e_). Distad of these facets is
a rough ridge.

The _third_ (3). The proximal end of its base is a triangular facet with
the apex directed ventrad and the sides excavated. It is for the distal
end of the lateral cuneiform (_e_). Its medial surface presents a
depression which receives the ridge of the second metatarsal. On the
lateral surface a short distance distad of the proximal border is a
triangular concave facet, and near the proximal border ventrad a second
concave facet. Both are for the fourth metatarsal.

The _fourth_ (4). The proximal end is convex, notched medially and
facetted for the cuboid (_c_). Its medial surface bears dorsad, a short
distance from its proximal end, a smooth tubercle, and ventrad a small
convex facet. Both articulate with facets on the lateral surface of the
third metatarsal. The lateral surface has a sinuous facet along its
dorsal border, and ventrad of this a depression. There is a second facet
along the ventral border. Both facets are for the fifth metatarsal, and
the depression is for ligaments.

The _fifth_ (5) has its base flattened and expanded so as to be
wedge-shaped, with the apex of the wedge directed proximad. Its dorsal
end extends into a tubercle. It thus presents only lateral and medial
surfaces. The medial surface shows two tubercles, one distad of the
other. The distal tubercle and the distal half of the proximal tubercle
are facetted and fit into the sinuous facet on the fourth metatarsal. A
narrow facet on the ventral border of the surface articulates with the
facet on the ventral border of the lateral surface of the fourth
metatarsal. The proximal half of the distal tubercle is facetted for the
cuboid (_c_). The lateral surface is smooth, non-articular, and
obliquely grooved.

_Phalanges_ (Fig. 58, _i_, _j_, _k_).--There are three phalanges in each
of the four digits, and these are almost identical with those described
for the manus.

_Sesamoid Bones._ _Ossa sesamoidea_ (Fig. 58, _l_).--The sesamoid bones
are found at the joints between the metatarsals and phalanges, and are
in all respects like those of the manus.


JOINTS AND LIGAMENTS OF THE PELVIC LIMBS.

_Ligaments of the Pelvis._--The ilium and sacrum are articulated at the
auricular facet of the ilium and the corresponding rough surface of the
sacrum. The joint is an amphiarthrosis, permitting very little movement.
A =capsular ligament= surrounds the articular surface, being attached to
the bones about its circumference; it is short and strong. Craniad of
the capsule is a thick very short ligament, composed of very strong
transverse fibres passing from the rough surface of the sacrum to the
corresponding rough surface of the ilium. This forms the =lateral
iliosacral ligament=, which is united at its caudal border to the
capsule.

A strong, wide ligamentous band passes from the dorsal border of the
ilium to the sides of the sacrum. This is indistinctly subdivided into
several bands, which together represent the =long= and =short posterior
iliosacral ligaments= of man.

_Symphysis pelvis._--The medial borders of the pubis and ilium meet in
the middle line ventrad of the pelvis and are here united by cartilage.
The joint is strengthened by numerous small bands which pass across the
line of junction from one side to the other; these occur on both
surfaces.

_The Hip-joint._--The hip-joint is an =enarthrosis=, or ball-and-socket
joint in which more than half the spherical head of the femur is
received into the acetabulum. The depth of the acetabulum is increased
by a rim of fibrocartilage about its margin, forming the =labrum
glenoidale=. This passes across the acetabular notch, forming the
=transverse ligament= of the acetabulum; beneath it blood-vessels and
nerves pass into the acetabular cavity.

The =capsule of the joint= is large and loose. It is attached about the
margin of the acetabulum, and passes over the head of the femur, to be
attached to the bone several millimeters distad of the head. It thus
encloses both the head and the neck of the femur.

The =ligamentum teres=, or round ligament, is a very strong, short
ligament which passes from the depression in the head of the femur to
the bottom of the acetabulum.

=The Knee-joint= (Figs. 60 and 61).--The joint between the femur and the
tibia is very complex. The surfaces of the condyles of the femur do not
correspond to those of the condyles of the tibia. Between the ends of
the two bones are placed two disks of cartilage, the =menisci=, or
semilunar cartilages (Fig. 60, _c_ and _d_; Fig. 61, _a_ and _b_), of
such a form that the congruity of articular surfaces is restored. Each
meniscus has a proximal surface corresponding to the form of one of the
condyles of the femur, and a distal surface corresponding to a condyle
of the tibia. The menisci are held in position by ligaments. The
knee-joint permits not only backward and forward movement, but also a
small amount of rotary motion.

The joint has two =capsules=, one on the dorsal (convex) side, the other
on the ventral side. The two communicate only by a small passageway
lying within the joint between the ends of the bones. The dorsal one is
attached to the femur several millimeters proximad of the patellar
surface and some distance on each side of the latter. The patella is
imbedded in its outer wall, and it is attached to the tibia on the edges
of the articular surface of the latter, from the crest to the
tuberosities. The capsule is also attached laterally and medially to
the sides of the menisci, and is closely united to the patellar
ligaments. Its cavity contains a mass of yellow fat.

The ventral capsule is attached to the borders of the articular surfaces
of the femur and tibia on their ventral sides, to the menisci, and to
the epicondyles of the femur and the tuberosities of the tibia. Its
walls are stronger and its cavity smaller than those of the dorsal
capsule.

The ligaments of the knee-joint (Figs. 60 and 61), aside from the
capsules, may be classified into: (1) those which are connected with the
patella; (2) =collateral= ligaments (Fig. 60, _i_ and _j_), which pass
from the epicondyles directly distad along the sides of the joint to the
tibia or fibula; (3) =crucial= ligaments (Fig. 60, _g_ and _h_; Fig. 61,
_c_ and _d_), which cross within the joint from one side of the femur to
the opposite side of the tibia; (4) ligaments which hold the menisci in
place (Fig. 60, _e_ and _f_; Fig. 61, _e_ and _f_).

(1) LIGAMENTS OF THE PATELLA.--The patella is imbedded in the dorsal
wall of the dorsal capsule of the joint. From its distal end a strong
tendon or ligament passes distad to the crest of the tibia. This is
known as the =ligamentum patellæ=: it may be considered a part of the
tendon of M. quadriceps femoris. On the lateral side the capsule of the
joint is strengthened by the transverse fibres of the tendon of M.
plantaris, which aid in holding the patella in place.

(2) COLLATERAL LIGAMENTS.--Of these there are two. The =ligamentum
collaterale fibulare= (Fig. 60, _j_) is attached to the lateral
epicondyle of the femur and passes distad across the tendon of the
plantaris muscle to the head of the fibula. Dorsad of the fibular
ligament and parallel with it passes the tendon of origin of the
extensor longus digitorum. The =ligamentum collaterale tibiale= (Fig.
60, _i_; Fig. 61, _g_) begins on the medial epicondyle of the femur and
passes distad to the lateral tuberosity of the tibia; part of it passes
one to one and a half centimeters distad of the tuberosity to be
attached to a rough ridge on the side of the tibia.

  [Illustration: FIG. 60.--KNEE-JOINT, FROM THE DORSAL OR PATELLAR SIDE.

  FIG. 61.--KNEE-JOINT, FROM THE VENTRAL OR FLEXOR SIDE.

  Fig. 60.--The patella has been removed. 1, femur; 2, tibia; 3,
  fibula. _a_, patellar surface of femur; _b_, tubercle for attachment
  of ligamentum patellæ; _c_, medial meniscus; _d_, lateral meniscus;
  _e_, _f_, ligaments of the menisci; _g_, ligamentum cruciatum
  anterius; _h_, ligamentum cruciatum posterius; _i_, ligamentum
  collaterale tibiale; _j_, ligamentum collaterale fibulare.

  Fig. 61.--The capsule of the joint has been opened. 1, femur; 2, tibia
  (fibula not shown); 3, sesamoid bone in lateral head of M.
  gastrocnemius; 4, sesamoid in medial head of M. gastrocnemius; 5,
  tendon of M. popliteus, with sesamoid bone; 6, 7, lateral and medial
  condyles of the femur, with the intercondyloid notch between them; 8,
  9, lateral and medial condyles of the tibia, with the popliteal notch
  between them; _a_, _b_, medial and lateral menisci; _c_, ligamentum
  cruciatum anterius; _d_, ligamentum cruciatum posterius; _e_, _f_,
  ligaments of the lateral meniscus; _g_, ligamentum collaterale
  tibiale.]

(3) CRUCIAL LIGAMENTS.--There are two of these also. The =ligamentum
cruciatum anterius=, or anterior crucial ligament (Fig. 60, _g_; Fig.
61, _c_), is a thick, strong ligament which begins on the dorsal part of
the proximal end of the tibia nearer the medial side (Fig. 60, _g_), and
passes ventrad and proximad, between the ends of the two bones forming
the joint, into the intercondyloid fossa of the femur, and becomes
attached to the medial surface of the lateral condyle of the femur (Fig.
61, _c_). It is composed of two partially separated bands, forming a
slight angle with one another. It is crossed near its dorsal and ventral
ends by two of the ligaments of the menisci. The =ligamentum cruciatum
posterius=, or posterior crucial ligament (Fig. 60, _h_; Fig. 61, _d_),
begins on the tibia at the edge of the popliteal notch (Fig. 61, _d_),
nearer the medial side, and passes dorsad and proximad to be attached to
the ventral edge of the patellar surface of the femur, in the
intercondyloid fossa (Fig. 60, _h_).

(4) LIGAMENTS OF THE MENISCI.--There are five of these, connecting the
menisci with the femur or tibia. One (Fig. 60, _e_) passes from the
dorsal edge of the medial meniscus (_c_) transversely across the
anterior crucial ligament (_g_) to the proximal end of the tibia nearer
the lateral side. A second (Fig. 60, _f_) passes from the dorsal margin
of the lateral meniscus (_d_) transversely beneath the anterior crucial
ligament (_g_) to the proximal end of the tibia nearer the ventral side
and medial border. A third (Fig. 61, _f_) passes from the ventral margin
of the lateral meniscus obliquely across the anterior crucial ligament
(_c_) to the lateral side of the medial condyle of the femur. The fourth
(Fig. 61, _e_) is small, passing from the medial angle of the ventral
border of the lateral meniscus distad to the popliteal notch. The fifth
passes from the ventral border of the medial meniscus laterad beneath
the posterior crucial ligament to the proximal end of the tibia, nearer
the ventral and lateral sides.

=Articulations between the Tibia and Fibula.=--At the proximal end the
fibula is as it were suspended from the distal side of the overhanging
lateral tuberosity of the tibia by strong ligamentous tissue. The
capsule of the joint is formed by an extension of the capsule of the
knee-joint which passes between the tibia and fibula on the ventral
side. Forming the dorsolateral wall of this extension is a strong, thick
ligament which passes directly from the head of the fibula to the
lateral surface of the lateral tuberosity of the tibia. A second more
delicate ligament passes from the head of the fibula dorsoproximad to
the tubercle laterad of the crest of the tibia, bridging a groove
through which passes the tendon of M. extensor longus digitorum.

The tibia and fibula are connected throughout their length by an
=interosseus membrane=. This is broad and very thin in its proximal
part, narrower and thicker distad.

Distad the two malleoli forming the ends of the fibula and tibia are
closely and immovably united. The capsule of the joint is here an
extension proximad of the capsule of the articulation with the
astragalus. On the dorsal side a short broad band of strong fibres
passes from the surface of the tibia obliquely laterodistad to the
border of the fibula; this forms the =anterior ligament= of the =lateral
malleolus=. On the ventral side a very much weaker set of fibres forms
the ventral wall of the articular capsule; it is called the =posterior
ligament= of the =lateral malleolus=. Tibia and fibula are also
connected on the dorsal side by the =ligamentum transversum cruris=, or
transverse ligament of the lower leg (Fig. 91, 5), which spans the
tendons of Mm. extensor longus digitorum and tibialis anterior. From the
middle of the distal margin of this a slender supporting ligament passes
distad and is inserted on the dorsal surface of the tarsus. The grooves
in the two malleoli for the passage of the tendons are spanned by
ligamentous fibres (retinacula) for holding the tendons in place.

=Articulation between the Leg and the Foot.=--At the distal end there is
formed between the two malleoli a deep irregular fossa, into which is
received the trochlea of the astragalus. The joint is covered by a
large =articular capsule=, which passes also, as above noted, between
the tibia and fibula. In addition to the capsule the following ligaments
may be distinguished: (_a_) On the lateral side, (1) a short ligament
from the fibula to the astragalus, directed toward the proximal end of
the foot; (2) a ligament from the fibula to the calcaneus, attached to
the latter proximad of the peroneal tubercle; (3) a stronger ligament
from the fibula to the calcaneus, lying beneath the last-mentioned and
directed toward the proximal end of the bone. (_b_) On the medial side
may be distinguished (1) a strong ligament from the tibia (medial
malleolus) to the sustentaculum tali, and passing thence onto the
scaphoid; (2) a short ligament from the medial malleolus to the
astragalus.

=The Tarsus.=--The articulations between the separate bones of the
tarsus and between the tarsus and metatarsus have a considerable number
of variously communicating articular capsules. The separate bones are
connected by many ligaments. The ligaments of the ventral surface
(=ligamenta plantaria=) are especially well developed. Here may be
noticed particularly a very large =calcaneocuboid= ligament, and a large
=calcaneocuneiform= ligament which passes from the sustentaculum tali to
the medial cuneiform. Those on the dorsal surface (=ligamenta dorsalia=)
are less strong and numerous. Many ligaments, longitudinal, transverse,
and oblique, pass also between the separate bones (=ligamenta
interossea=). =Ligamenta lateralia=, on the lateral and medial borders
of the foot, are also distinguishable. Strauss-Durckheim enumerates
ninety-four ligaments of the tarsus; an account of each of these does
not form part of the plan of the present work.

The ligaments of the metatarsus and phalanges are of the same general
character as in the forelimb. Of these Strauss-Durckheim enumerates
thirty-six; they will not be described here.



THE MUSCLES.


=I. THE MUSCLES OF THE SKIN.= (Fig. 62.)

=M. cutaneus maximus= (Fig. 62, _b_).--This is a very large, thin muscle
which covers almost the whole side of the body. It arises from the outer
surface of the latissimus dorsi (Fig. 68, _m_) near its ventral end and
from the bicipital arch (Fig. 65, _t′_) in the axilla; from the linea
alba for a considerable distance (two or three inches) caudad of the
base of the xiphoid process, and from the thorax over a line joining the
axilla and the base of the xiphoid. Sometimes a few fibres take origin
from the fascia which covers the pectoantibrachialis on the ventral side
of the arm.

From their origin the fibres diverge. The cranial ones curve about the
base of the forelimb and are inserted into the skin at or near the
middle line caudad of the first thoracic vertebra. The most cranial
fibres of all are inserted about one to one and a half centimeters from
the middorsal line; thence the line of insertion approaches the
middorsal line to reach it at about the eighth or ninth thoracic
vertebra. The middle fibres run parallel to the middorsal line in the
lumbar and sacral regions as far as the root of the tail, a small bundle
passing onto the dorsal side of the tail, another onto the ventral side.
The fibres of the caudal portion pass onto the thigh, the ventral ones
running in the fold of skin which stretches from thigh to abdomen, and
are finally lost in the fascia along a line connecting the knee and the
root of the tail. A strong fascia connects the adjacent borders of the
cutaneus and platysma and lies over the scapular region.

  [Illustration: FIG. 62.--MUSCLES OF THE SKIN.

  _a_, _a_′, _a_″, M. platysma; _b_, M. cutaneus maximus; _c_, M.
  orbicularis oris. Between the platysma and the cutaneus maximus are
  seen the following deeper muscles: _d_, M. acromio-trapezius; _e_, M.
  levator scapulæ ventralis; _f_, M. spino-deltoideus; _g_, M.
  acromio-deltoideus; _h_, M. clavobrachialis; _i_, caput laterale of M.
  triceps brachii; _j_, caput longum of M. triceps brachii; _k_, M.
  xiphi-humeralis; _l_, M. pectoralis minor. 1, external jugular vein.]

This muscle lies immediately beneath the integument. It covers the first
layer of body muscles.

_Action._--Moves the skin.

=M. platysma= (Figs. 62 and 64, _a_, _a′_, _a″_).--This muscle forms a
thin layer of fibres covering the sides of the neck and face, in close
relation with the integument. Several more or less distinct portions may
be distinguished.

(1) Most of the fibres (_a_) arise from the middorsal line, from the
occiput to the first thoracic vertebra, in a narrow fascia common to the
muscles of the two sides. The most cranial fibres of this region arise
as a small bundle from the external occipital crest, beneath the
levator auris longus (Fig. 63, _g_, _g′_).

From this origin in the middle line the fibres pass craniolaterad. The
most cranial fibres curve about the ventral side of the ear and pass
toward the caudal angle of the eye, where they unite with fibres of the
zygomaticus (Fig. 64, _d_) or corrugator supercilii lateralis (Fig. 64,
_k_), or pass to the lower eyelid. Caudad of these the fibres cover the
side of the face and become lost among the facial muscles, some passing
to the lower eyelid, some to the fibrous pad which supports the
vibrissæ, some to the angle of the mouth, some to the lower lip. The
most ventral fibres meet the fibres of the opposite muscle just ventrad
of the symphysis of the mandible.

The ventral free border of the platysma is separated on the ventral side
of the neck from the border of the opposite muscle by a wedge-shaped
area having its point at the symphysis menti.

The fibres of this portion of the muscle are interrupted by an
attachment to the skin, along a line passing from the base of the ear to
about the middle of the coracoid border of the scapula, The dorsal (_a_)
and ventral (_a′_) portions of the muscle, separated by this line of
attachment, are sometimes described as separate muscles (the
=supercervicocutaneus= and =cervicofacial=, respectively, of
Strauss-Durckheim).

(2) A band of fibres one or two centimeters across (_a″_) arises in the
fascia of the side of the neck just craniad of the middle of the
coracoid border of the scapula, and passes caudoventrad toward the
manubrium, its fibres crossing the fibres of the first part of the
platysma at right angles. These fibres become lost in the fascia ventrad
of the manubrium, or pass across the middle line to intermingle with the
corresponding fibres of the opposite side. This portion of the platysma
is sometimes absent.

The platysma is everywhere subcutaneous, except at its dorsocranial
angle, where a small bundle of fibres is covered by the levator longus
auris. It covers the deeper muscles of the neck and head. Closely
attached to its inner surface are the submentalis and depressor conchæ,
whose fibres bridge over the ventral interval between the borders of the
platysmas of opposite sides.

_Action._--Moves the skin of the face and neck.


=II. THE MUSCLES OF THE HEAD.=


A. SUPERFICIAL MUSCLES.--The most superficial layer of muscles on the
face and head is formed by differentiation of the fibres of the
platysma. The muscles thus formed are not clearly distinct from each
other; in this region sets of fibres differing in direction and in
origin or insertion receive separate names even though the different
sets of fibres are closely interwoven.

In the quadrangle on the dorsal surface of the head enclosed between the
two eyes and the two ears, a thin superficial sheet of fibres is found,
in which a number of different sets may be distinguished (Fig. 63).
These have received the following names.

=M. intermedius scutulorum= (Fig. 63, _a_).--This consists of a broad
thin sheet of transverse fibres between the two external ears. The
fibres are attached at either end to the scutiform cartilage (1) of
the two ears, and pass without interruption across the middle line. At
its cranial edge this muscle is continuous with the corrugator
supercilii medialis (_b_); at its lateral edge with the
frontoscutularis; at its caudal edge with the levator auris longus
(_g_).

_Relations._--Outer surface with the integument. Inner surface with the
galea aponeurotica (to which the muscle is closely united), the
epicranius muscle (_h_) and the temporal muscle (_n_).

_Action._--Draws the two ears dorsad, toward the middle line.

  [Illustration: FIG. 63.--MUSCLES ON THE DORSAL SURFACE OF THE HEAD.

  On the right side are shown the superficial muscles; on the left side
  the superficial muscles have mostly been removed, exposing the deeper
  muscles and the bone. _a_, M. intermedius scutulorum; _b_, M.
  corrugator supercilii medialis; _c_, M. orbicularis oculi; _d_, M.
  corrugator supercilii lateralis; _e_, cranial end fibres of M.
  platysma; _f_, M. adductor auris superior; _g_, _g′_, M. levator auris
  longus (_g_, cranial portion; _g′_, caudal portion); _h_, _h′_, M.
  epicranius (_h_, M. occipitalis; _h′_ M. frontalis); _i_, M.
  transversus auriculæ; _k_, M. auricularis superior (cut on the left
  side); _l_, M. abductor auris brevis; _m_, M. abductor auris longus;
  _n_, M. temporalis; _o_, cut origin of M. frontoscutularis; _p_, _p′_,
  M. levator labii superioris alæque nasi (_p′_, the origin from the
  maxillary bone); _q_, angular head of M. quadratus labii superioris.
  1, scutiform cartilage; 2, external ear; 3, bones of the skull.]

=M. corrugator supercilii medialis= (_b_).--This consists of a thin
sheet of scattered fibres lying craniad of the last and intermingling
with it. The fibres take origin near the middle line, pass laterad, then
curve craniad, converging, to be inserted into the whole extent of the
upper eyelid, especially near the caudal angle. Here the fibres unite
with those of the orbicularis oculi (_c_).

This muscle is continuous caudad with the intermedius scutulorum (_a_),
craniad with the orbicularis oculi (_c_); laterad with the corrugator
supercilii lateralis (_d_). Toward the medial side the fibres lose
themselves in a tendinous sheet that joins the galea aponeurotica.

_Relations._--Outer surface with the integument. Inner surface with the
frontoscutularis and the skull.

_Action._--Raises the upper eyelid.

=M. orbicularis oculi= (Fig. 63, _c_; Fig. 64, _s_).--This consists of
two thin bands of muscle-fibres which lie one in either eyelid parallel
to its border and unite at the angle of the eye.

_Origin_ by short tendon-fibres from a tubercle on the surface of the
frontal process of the maxillary bone just dorsad of the orbital end of
the lachrymal canal and between the two parts of the quadratus labii
superioris (Fig. 63, _p_ and _q_).

The muscle splits into two parts which pass into the two eyelids. At the
outer angle of the eye the two bands unite by the intervention of
tendon-fibres between the muscle-fibre bundles of the two.

_Relations._--Outer surface with the integument. Inner surface with the
inner membrane of the eyelid.

_Action._--Closes the eye.

=M. corrugator supercilii lateralis= (Fig. 63, _d_; Fig. 64, _k_).--This
consists of a number of scattered fibres which arise from among the
fibres of the frontoscutularis, and from the tendon lying just craniad
of the external opening of the ear, to which are united also parts of
the zygomaticus (Fig. 64, _d_) and submentalis (Fig. 64, _c_). The
fibres pass craniad, converging so as to form a narrow band which is
inserted at the caudolateral angle of the eye, where it unites with the
orbicularis oculi (Fig. 64, _s_). This muscle is continuous on the
medial side with the corrugator supercilii medialis (Fig. 64, _j_) and
the frontoauricularis, on the lateral side with the platysma.

_Relations._--Outer surface with the integument. Inner surface with the
frontal bone and the frontoscutularis.

_Action._--Pulls the angle of the eye caudad; at the same time pulls the
external ear craniad.

=M. frontoauricularis.=--A few of the fibres which are attached along
the upper eyelid sometimes pass dorsocaudad, mingled with fibres of the
corrugatores supercilii medialis and lateralis and the frontoscutularis,
to the craniomedial angle of the auricular cartilage, where they unite
with the fibres of the adductor auris superior. These fibres are
sometimes distinguished as the =frontoauricularis= muscle.

=M. levator auris longus= (Fig. 63, _g_ and _g′_). (Part of the
auricularis posterior of man.)--This lies on the caudal half of the
dorsal surface of the head, forming a laterocaudal continuation of the
intermedius scutulorum (_a_).

_Origin_ from the middle line of the neck dorsad of the atlas, and from
the sagittal crest for about one centimeter craniad of the external
occipital tubercle. The fibres form a broad thin sheet which passes
craniolaterad as far as the caudal end of the scutiform cartilage (1).
Here the muscle divides; the major portion is attached to the scutiform
cartilage (1), its fibres intermingling with those of the intermedius
scutulorum (_a_). The caudal portion of the muscle (_g′_) passes onto
the surface of the auricle, extending one or two centimeters distad;
here it is inserted on an oblique line which lies directly craniad of
the insertion of the transversus auriculæ (_i_).

The caudal portion of this muscle (_g′_) having origin above the atlas
and insertion on the auricle, is sometimes considered a separate muscle,
the supercervicoauricular or cervicoauricular. The cranial portion (_g_)
with origin on the sagittal crest and insertion on the scutiform
cartilage might be distinguished as the occipitoscutularis.

The levator auris longus is continuous at its cranial end medially with
M. epicranius (_h_); laterally with M. intermedius scutulorum (_a_).

_Relations._--Outer surface with the integument. Inner surface with the
temporal muscle (_n_), the auricularis superior (_k_), the abductor
longus auris (_m_), a narrow strand of the platysma, and the
clavotrapezius.

_Action._--Pulls the external ear dorsocaudad.

The four following muscles lie partly or entirely beneath those already
described; they are doubtless formed as differentiations of the inner
layers of the platysma.

=M. auricularis superior= (or attollens auris) (Fig. 63, _k_).--This
muscle forms a band about one centimeter broad lying just beneath the
levator longus (_g_).

_Origin_ on the sagittal crest for about one centimeter craniad of the
interparietal bone. The muscle passes laterad onto the surface of the
auricle and is inserted into the auricular cartilage a little caudad of
the middle of its convex surface. At its lateral end the cranial margin
is closely united to the under surface of the levator auris longus
(_g_).

_Relations._--Outer surface at the medial end with the epicranius (_h_),
the abductor auris longus (_m_), and levator auris longus (_g_); at the
lateral end with the skin. Inner surface with the temporal muscle (_n_)
and the auricular cartilage.

_Action._--Pulls the external ear dorsad.

=M. abductor auris longus= (Fig. 63, _m_; Fig. 64, _q_). (Part of the
auricularis posterior of man.)

_Origin_ on the sagittal crest dorsad of the interparietal bone, caudad
of that of the auricularis superior (_k_), which it partly covers.

The muscle passes laterad as a flat band 8 to 10 millimeters wide over
the caudal surface of the concha of the ear, and is inserted (Fig. 64,
_q_) on the lateral surface of the eminentia conchæ, caudad of the
antitragus.

_Relations._--Outer surface with the levator auris longus (_g_) and the
integument. Inner surface with the auricularis superior (_k_), the
abductor auris brevis (_l_), and the concha.

_Action._--Pulls the external ear caudad.

=M. abductor auris brevis= (Fig. 63, _l_).

_Origin_ by a tendon from the lambdoidal crest for one or two
centimeters laterad of the middle.

The muscle passes lateroventrad lying beneath the abductor longus (_m_)
as a flat band 6 to 8 millimeters wide which is inserted into the medial
surface of the most proximal portion of the concha, just distad of its
junction with the cartilaginous auditory meatus.

_Relations._--Outer surface with the abductor longus (_m_), a small
strand of the platysma and the concha. Inner surface with the temporal
muscle (_n_).

_Action._--Pulls the concha caudad.

=M. epicranius= (or occipitofrontalis) (Fig. 63, _h_ and _h′_).

_Origin_ on the sagittal crest or suture, just craniad of the origin of
the levator longus auris, to the inner surface of which this muscle is
closely united. From the origin the fibres pass craniad forming a band
(_h_) about 8 or 10 millimeters in width, the two muscles lying close to
one another and partly united in the middle line. About two centimeters
craniad of their origin the fibres of both muscles end in a tendinous
sheet, the =galea aponeurotica=, which covers the surface of the skull
in the region between the ears and eyes, and is formed by the inner
surface of the intermedius scutulorum (_a_) and other muscles of this
region. The galea aponeurotica passes craniad onto the surface of the
nose, where it gives origin again to a thin sheet of muscle-fibres
(_h′_) which are inserted into the integument near the cranial ends of
the nasal bones.

M. epicranius is thus formed of two muscular portions (_h_ and _h′_),
connected by a long tendinous sheet. The caudal portion is frequently
distinguished as the occipital muscle (=M. occipitalis=, _h_), the
cranial portion, on the nose, as the =frontal= muscle (=M. frontalis=,
_h′_).

_Relations._--Outer surface of the occipitalis (_h_) with the
intermedius scutulorum (_a_), the levator auris longus (_g_), and the
integument; inner surface with the auricularis superior (_h_), the
abductor auris longus, and the bone. Outer surface of the frontalis
(_h′_) with the integument; inner surface with the bones of the skull.

_Action._--Moves the integument of the dorsal surface of the head and of
the nose.

Ventrad of the external ear the following three differentiated portions
of the platysma may be distinguished.

=M. zygomaticus= (major) (Fig. 64, _d_).--A slender band connecting the
angle of the mouth with the scutiform cartilage of the ear.

  [Illustration: FIG. 64.--SUPERFICIAL MUSCLES ON THE LATERAL SURFACE OF
  THE HEAD AND NECK.

  _a_, _a′_, _a″_, M. platysma; _b_, M. depressor conchæ; _c_, M.
  submentalis; _d_, M. zygomaticus (_b_, _c_, and _d_ lie beneath the
  platysma and are seen through it); _e_, M. zygomaticus minor; _f_′, M.
  caninus; _f_, _g_, parts of M. quadratus labii superioris (_f_,
  angular head; _g_, M. levator labii superioris alæque nasi); _h_, M.
  myrtiformis; _i_, M. orbicularis oris; _j_, M. corrugator supercilii
  medialis; _k_, M. corrugator supercilii lateralis; _l_, M. adductor
  auris superior; _m_, M. helicis; _n_, M. antitragicus; _o_, M.
  adductor auris inferior; _p_, M. conchæus externus; _q_, M. abductor
  auris longus; _r_, parts of M. auricularis externus; _s_, M.
  orbicularis oculi.]

At the angle of the mouth the fibres arise from among those of the
orbicularis oris (_i_), from both the upper and the lower lip. They pass
thence dorsocaudad across the zygomatic arch as a band 8 or 10
millimeters wide which is attached to a tendinous aponeurosis lying just
craniad of the external opening of the ear. To this aponeurosis are
attached also, wholly or partly, the corrugator supercilii lateralis
(_k_) and the submentalis (_c_). The aponeurosis is united with the
caudoventral angle of the scutiform cartilage and with the ventral edge
of the cranial margin of the auricular cartilage.

This muscle is united at its cranial end with the orbicularis oris
(_i_); throughout its length more or less with the platysma (_a_, _a′_);
at its caudodorsal end with the corrugator supercilii lateralis (_k_) on
its medial side, and with the submentalis (_c_) on its lateral side.

_Relations._--Outer surface with the integument and the platysma (_a′_).
Inner surface with the masseter, temporal, frontoscutularis, and
adductor auris inferior (_o_).

_Action._--Draws the angle of the mouth dorsocaudad; the external ear
ventrocraniad.

=M. submentalis= (Fig. 64, _c_).--A flat band, similar to the last, and
closely connected for some distance to its caudal border.

It arises as scattered fibres near the ventral middle line at about the
level of the larynx, the fibres of the opposite muscles crossing the
middle line and intermingling. The fibres pass dorsad, converging so as
to form a narrower band, which unites dorsad with the zygomaticus (_d_),
to be inserted with it into the tendinous aponeurosis above described.

_Relations._--Outer surface with the integument and platysma (_a′_).
Inner surface with the muscles of the hyoid, the digastricus, the
parotid gland, the masseter, the zygomatic arch and the temporal muscle.

_Action._--Draws the external ear ventrad.

=M. depressor conchæ= (Fig. 64, _b_).--A thin band of fibres, caudad of
the last and parallel with it. The muscle arises as scattered fibres on
the ventral surface of the neck, one or two centimeters craniad of the
manubrium, the fibres of the muscles of opposite sides crossing the
middle line and interdigitating. They pass dorsad, gathering together to
form a narrow band which is inserted into the summit of the antitragus.

_Relations._--Outer surface with the skin at the ventral end, and with
the platysma (_a′_) further dorsad. Inner surface with the deep muscles
of the neck and with the parotid gland.

_Action._--Draws the external ear ventrad.

Lying deeper than the muscles thus far described, but closely connected
with a number of them, are the following:

=M. frontoscutularis.=

_Origin_ (Fig. 63, _o_) on the frontal bone, along the supraorbital
margin, from the craniomedial angle of the eye caudad to the zygomatic
process of the frontal.

The fibres form a large muscle which passes dorsocaudad to the scutiform
cartilage and is mostly attached along its ventrolateral border. Some of
the outer fibres, however, pass distad of the scutiform cartilage toward
the cartilage of the ear, thus joining the adductor auris superior
(_f_).

The outer surface of this muscle is closely connected with fibres of
the intermedius scutulorum (_a_), the corrugatores supercilii medialis
(_b_) and lateralis (_d_), and the frontoauricularis, when this exists.
The outer surface is covered near the origin by the orbicularis oculi
(_c_), farther dorsad by the muscles just mentioned and the integument.
The inner surface is in relation with the frontal bone and the adductor
auris inferior (Fig. 64, _o_).

_Action._--Pulls the ear craniad.

=M. adductor auris inferior.= (Fig. 64, _o_.) (Part of the auricularis
anterior of man.)--A small muscle lying beneath the frontoscutularis.

_Origin_ on the ligament which connects the zygomatic process of the
frontal with the frontal process of the malar. The fibres form a thin
band about 7 millimeters wide which passes craniad, closely united to
the inner surface of the frontoscutularis. At the caudal edge of the
zygomaticus (_d_) the muscle is interrupted by a short tendinous
interval; the fibres then continue to their insertion on the tip of the
antitragus.

_Relations_.--Outer surface with the frontoscutularis, the zygomaticus
(_d_), and the integument. Inner surface with the temporal muscle and M.
antitragicus (_n_).

_Action._--Pulls the ear craniodorsad.

       *       *       *       *       *

The remainder of the muscles of the ear, which, with the exception of
the tragicus lateralis, merely interconnect the cartilages of the
external ear or parts of these cartilages, are described in connection
with the account of the Auditory Organ.

       *       *       *       *       *

Owing to the presence of the fibrous pad to which the whiskers are
attached, the facial muscles between the eye and the mouth differ in the
cat in some respects from those of related animals. This fibrous pad
interrupts the muscles, frequently breaking muscles which are elsewhere
single into two.

=M. zygomaticus minor=, or malaris (Fig. 64, _e_).--This muscle is not
always present; when it exists it forms a very thin flat band of fibres
passing from the ventral side of the eye toward the angle of the mouth.

_Origin_ among the fibres of the orbicularis oculi (_s_) in the lower
eyelid. The fibres pass ventrad; the insertion varies. In some specimens
the insertion is among the fibres of the orbicularis oris (_i_), at the
angle of the mouth, beneath the zygomaticus (_d_). In other cases this
muscle is said to be inserted into the pad on which the whiskers rest.

_Relations._--Outer surface with the integument and near its insertion
with the zygomaticus major (_d_). Inner surface with the malar bone and
the masseter muscle.

_Action._--Pulls the angle of the mouth (or the whiskers) dorsad.

=M. orbicularis oris= (Fig. 64, _i_).--This forms a very thin layer of
subcutaneous concentric fibres which surround the mouth, that of the
upper lip being thicker than that of the lower lip. The part of the
muscle in the lower lip has its fibres intermingled with those of the
platysma (_a′_). In the median line the fibres of the upper lip are
interrupted by a raphe, and caudad of this are intermingled with those
of the caninus.

=M. quadratus labii superioris= (Fig. 63, _p_ and _q_; Fig. 64, _f_ and
_g_).--This is a complex of muscle-fibres attached chiefly to the
fibrous pad on which the whiskers rest. In it two parts can be
distinguished more or less completely.

(1) =M. levator labii superioris alæque nasi= (Fig. 63, _p_; Fig. 64,
_g_) on the sides of the nose. This arises (_a_) as a continuation of
the frontal portion of the epicranius, and (_b_) in a small bundle (Fig.
63, _p_) from near the dorsal end of the frontal process of the
maxillary bone, in common with the next. The two slips thus formed
unite craniad and are inserted partly into the integument on the outer
side of the wing of the nose, partly into the skin of the upper lip,
lateroventrad of the nose, and partly into the pad on which the whiskers
are located, in connection with the next.

(2) The =angular= head (=caput angulare=), or =levator labii superioris
proprius= (Fig. 63, _q_; Fig. 64, _f_) is much larger than the last. It
takes origin from a small tubercle at the cranial border of the orbit,
close to the origin of the orbicularis oculi. The fibres diverge from
their origin to their insertion among the whiskers and in the fibrous
pad on which the whiskers rest.

_Action._--Erects the whiskers and raises the upper lip.

=M. caninus= or =levator anguli oris= (Fig. 64, _f′_).

_Origin_ in a depression on the lateral surface of the maxillary bone,
just craniad of the last premolar tooth. The fibres pass craniad,
diverging, toward the whiskers, and have their insertion into the pad of
tissue on which the whiskers rest.

_Action._--Retracts the whiskers and raises the upper lip.

=M. buccinator.=--A thin muscle against the mucous membrane of the upper
lip, partly united with the orbicularis oris and lying beneath M.
caninus.

_Origin_ on the outer surface of the superior maxillary bone in the
depression between the infraorbital foramen and the first premolar
tooth. The fibres pass ventrad, diverging, and mingle with those of the
deep part of the orbicularis oris.

_Relations._--Outer surface with the caninus and with the orbicularis
oris. Inner surface with the mucous membrane of the upper lip.

_Action._--Raises the upper lip.

=M. myrtiformis= (probably corresponds to a part of the human M.
nasalis) (Fig. 64, _h_).--A thin sheet of muscle-fibres lying craniad of
the levator labii superioris alæque nasi and passing from the whiskers
to the nose and upper lip. It is distinguishable from the alæque nasi by
the direction of the fibres.

_Origin_ from the pad upon which the whiskers rest. The fibres diverge
and have their

_Insertion_ upon the wing of the nose and into the skin of the upper lip
near the median line.

_Action._--Dilator of the nares and elevator of the upper lip.

=M. “moustachier”= (Str.-D.) (probably corresponds to one of the Mm.
incisivi).--It lies on the upper lip near the median line.

_Origin_ from the outer surface of the premaxilla near the suture along
the ventral border of the narial opening. The fibres diverge and pass
caudad into the upper lip within the superficial fibres of the
orbicularis oris.

_Insertion._--The skin of the upper lip just craniad of the whiskers.
Some of the fibres pass into the pad on which the whiskers rest.

_Action._--It carries the lip craniad.

=M. quadratus labii inferioris.=--A thin flat band extending almost the
length of the lower lip.

_Origin_ from the alveolar border of the mandible, between the molar
tooth and the canine. The fibres pass dorsad into the lower lip, where
they intermingle with those of the orbicularis oris. The muscle is
perhaps not constant.

_Action._--Depressor of the lower lip.

Sometimes a few fibres arising from the cranial portion of the alveolar
border of the mandibula pass mediad, seeming to join corresponding
fibres from the opposite side. Such fibres would constitute a M.
transversus menti.


B. DEEP MUSCLES OF THE HEAD.


(_a_) _Muscles of Mastication._

=M. digastricus= (Fig. 65, _b_).--The digastric is a thick prismatic
muscle lying mediad of the angle of the lower jaw, connecting it with
the base of the skull.

_Origin_ by fleshy fibres from the outer surface of the jugular process
of the occipital bone, and by a thin tendon from the tip of the mastoid
process and from the ridge between the mastoid and the jugular
processes. The muscle passes craniad, becoming at the same time broader
and more voluminous.

_Insertion._--The ventral border of the mandible craniad of the caudal
border of the molar tooth. The insertion area extends slightly onto both
surfaces of the bone and is triangular, with its apex craniad.

_Relations._--Outer (ventral) surface with the following, beginning at
the caudal end: the rectus capitis lateralis, the cleidomastoid (_h_),
the submaxillary gland (2), the stylohyoid (_d_), a large lymph-gland
(3), and the integument. Inner (dorsal) surface with the jugulohyoid,
the tympanic bulla, the masseter (_a_), the hyoglossus, and the
mylohyoid (_c_).

_Action._--Depressor of the lower jaw.

=M. masseter= (Figs. 65 and 66, _a_).--The masseter forms the projecting
mass so prominent in the cat behind and below the eye. Its outer surface
is covered by a strong aponeurosis. The muscle is divided into three
layers which are distinct as to origin, insertion, and direction of
fibres, but which are otherwise not distinct.

The =superficial layer= takes

_Origin_ by the superficial aponeurosis from the ridge which runs
lengthwise of the outer surface of the malar bone, and by fleshy fibres
from the surface of the malar bone ventrad of this ridge. The fibres
pass obliquely caudad to their insertion.

_Insertion._--The caudal half of the lateral margin of the ventral
border of the mandible, by a sheet of fascia which lies on the inner
surface of the muscle. The superficial fibres curve ventrad of the
mandible and are inserted into a tendinous intersection between this
muscle and the internal pterygoid (Fig. 66, _c_).

The =middle layer= takes

_Origin_ from the ventral border of the malar bone, from opposite the
molar tooth to within three millimeters of the mandibular fossa. The
fibres pass ventrad and have their

_Insertion_ into the mandible at the ventral border of the external
coronoid fossa by means of the aponeurosis which covers the inner
surface of the muscle.

  [Illustration: FIG. 65.--MUSCLES ON THE VENTRAL SURFACE OF THE THORAX,
  NECK AND HEAD.

  The left side shows the first layer of muscles beneath the skin and
  skin-muscles; the right side shows the second layer, except in the
  head region. _a_, M. masseter; _b_, M. digastricus; _c_, M.
  mylohyoideus; _d_, M. stylohyoideus; _e_, M. sternohyoideus; _f_, M.
  thyreohyoideus; _g_, M. sternomastoideus; _g′_, M. sternothyreoideus;
  _h_, M. cleidomastoideus; _i_, M. levator scapulæ ventralis; _j_, M.
  clavotrapezius; _k_, M. clavobrachialis; _l_, M. pectoralis major;
  _m_, M. pectoantibrachialis; _n_, part of M. scalenus; _o_, M.
  pectoralis minor; _p_, M. xiphihumeralis; _q_, M. latissimus dorsi;
  _r_, M. epitrochlearis; _s_, caput longum of M. triceps brachii; _t_,
  M. biceps brachii; _t′_, bicipital arch; _u_, M. acromiodeltoideus;
  _v_, M. brachialis. 1, parotid gland; 2, submaxillary gland; 3,
  lymphatic glands; 4, external ear; 5, external jugular vein; 6,
  manubrium; 7, first rib; 8, common carotid artery; 9, molar gland.]

The =deep layer= takes

_Origin_ by a strong tendon from the ventral border of the zygoma just
craniad of the mandibular fossa. The fibres pass cranioventrad, diverge
and have their

_Insertion_ into the external coronoid fossa.

_Relations._--Outer surface with the following, beginning at the caudal
border: the external ear, the parotid gland (Fig. 65, 1), the platysma,
the submentalis, the zygomaticus (major), the zygomaticus minor. Ventral
border with a lymph gland caudad of the angle of the mouth (Fig. 65, 3),
and the digastric muscle (_b_). Inner surface with the bones.

_Action._--A very powerful elevator of the lower jaw.

=M. temporalis= (Fig. 63, _n_).--The temporal muscle is the great mass
taking origin from the temporal fossa and having its insertion on both
surfaces and both borders of the coronoid process of the mandible. It
may be divided into two layers, deep and superficial.

The =superficial layer=. The temporal fascia stretches over the temporal
fossa, being attached to its borders; that is, to the sagittal and
lambdoidal crests, to the curved ridge which connects the sagittal crest
with the zygomatic process of the frontal bone, to the caudal border of
this process, to the caudal border of the malar bone, to the caudal
border of the ligament connecting the malar bone and the zygomatic
process of the frontal, and to the dorsal border of the zygomatic
process of the temporal bone and its dorsal root. The craniolateral part
of this fascia is much stronger than the remainder.

The muscle-fibres take origin from the strong craniolateral part of the
inner surface of the temporal fascia, from the groove on the temporal
bone dorsad of the dorsal root of its zygomatic process, from the whole
inner surface of this process and of the zygomatic process of the malar
bone, and sometimes also from that part of the frontal bone which lies
within the temporal fossa.

_Insertion.-_-The outer surface of the coronoid process of the mandible
dorsad of the coronoid fossa, and both borders of the coronoid process.
The cranial fibres may be inserted craniad of the coronoid process onto
the aponeurosis covering the deep portion of the muscle. The caudal part
of this portion is more or less distinct and is sometimes described as
a separate head.

The =deep portion=.

_Origin_ by fleshy fibres from the whole surface of the temporal fossa,
except in cases where the cranial part of the fossa is occupied by the
superficial portion. The fibres converge toward the coronoid process,
and the ventral third of the outer surface is covered by strong fascia.

_Insertion._--The whole inner surface of the coronoid process of the
mandible.

_Relations._--Outer surface with the external ear, the ear-muscles (Fig.
63), the epicranius (Fig. 63, _h_), the corrugatores supercilii
lateralis (_d_) and medialis (_b_). Inner surface with the skull, the
pterygoideus externus (Fig. 66, _b_), and the structures within the
orbit.

_Action._--Elevator of the lower jaw.

=M. pterygoideus externus= (Fig. 66, _b_).--This lies on the medial side
of the mandible, ventrad of the ventral portion of the temporal.

_Origin._--The external pterygoid fossa (Fig. 40, _h_), which lies on
the lateral surface of the perpendicular plate of the palatine bone, and
on the surface of the pterygoid process of the sphenoid bone dorsad of
the internal pterygoid fossa. The fossa extends from the foramen
rotundum to the sphenopalatine foramen. The muscle passes with parallel
fibres laterad, ventrad, and caudad and has its

_Insertion_ by a strong flat tendon into the medial surface of the
mandible near its ventral border between the opening of the mandibular
canal and the base of the angular process.

_Relations._--Ventral surface with the masseter (_a_), the digastric,
and the soft palate with its muscles. Dorsal surface with the temporal,
and near its origin with the muscles of the eye, and other structures in
the orbit.

_Action._--Elevator of the lower jaw.

=M. pterygoideus internus= (Fig. 66, _c_).--This lies caudad of the
pterygoideus externus, nearly parallel to it, and is connected with it
at its lateral end.

_Origin_ from the whole surface of the internal pterygoid fossa (Fig.
40, _s_).

_Insertion_ by fleshy fibres into the ventral surface of the external
pterygoid and its tendon, into the medial surface of the angular process
of the mandible and caudad of the angular process for about one
centimeter into a fascia common to it and the masseter muscle, and into
the stylomandibular ligament.

  [Illustration: FIG. 66.--OBLIQUELY VENTRAL VIEW OF THE DEEP MUSCLES OF
  THE LOWER JAW AND PALATE.

  The tongue and other structures forming the floor of the mouth have
  been removed, showing the roof of the mouth. On the right side the
  masseter and pterygoideus internus have been removed, _a_, _a′_, M.
  masseter; _b_, M. pterygoideus externus; _c_, M. pterygoideus
  internus; _d_, _d′_, M. tensor veli palatini; _e_, _e′_, M. levator
  veli palatini; _f_, M. constrictor pharyngis superior. 1, aponeurosis
  of the velum palatinum; 2, ridges formed by the palatines and
  pterygoid portions of the sphenoid; 3, hamular processes; 4, free
  caudal border of the velum palatinum; 5, bulla tympani.]

_Relations._--Ventral surface with the styloglossus and the soft palate.
Dorsal surface with the bulla tympani (5) and base of the skull. Cranial
surface with the pterygoideus externus (_b_), with which it is partly
united.

_Action._--Assists the pterygoideus externus.


(_b_) _Muscles of the Hyoid Bone._

=M. stylohyoideus= (Fig. 65, _d_).--The stylohyoid is a ribbon-like
muscle about three millimeters wide. It lies on the superficial surface
of the digastric, caudad and ventrad of the angle of the jaw.

_Origin_ by fleshy fibres from the outer surface of the stylohyal bone
near its middle. The muscle curves over the outer surface of the
digastric (_b_), and ends about one centimeter from the middle line in a
slender flat tendon.

_Insertion_ into the middle of the ventral surface of the body of the
hyoid bone. Some of the fibres of the mylohyoid (_c_) are inserted into
its tendon.

_Relations._--Outer surface with the submaxillary gland (2) and the
submentalis muscle. Inner surface with the digastric (_b_), the
hyoglossus (Fig. 67, _h_), and the geniohyoid (Fig. 67, _g_).

_Action._--Raises the hyoid.

=M. geniohyoideus= (Fig. 67, _g_).--The geniohyoid is a long slender
muscle which lies next to the median line between the symphysis menti
and the hyoid bone, closely applied to its fellow of the opposite side
and within (dorsad of) the mylohyoid (Fig. 65, _c_).

_Origin_ from the ventral half of the inner surface of the mandibula for
about one millimeter from the symphysis.

_Insertion_ by muscle-fibres into the lateral half of the ventral
surface of the body of the hyoid bone.

_Relations._--Outer (ventral) surface with the stylohyoid (Fig. 65, _d_)
and the mylohyoid (Fig. 65, _c_); medial border with the muscle of the
opposite side. Lateral border with the hyoglossus (Fig. 67, _h_) and
genioglossus (Fig. 67, _f_). Inner (dorsal) surface with the
genioglossus.

_Action._--Draws the hyoid forward.

=M. jugulohyoideus= (Fig. 67, _b_).--The jugulohyoid is a small flat
quadrangular muscle covering the outer part of the ventral surface of
the tympanic bulla.

_Origin_ from the ventral border of the jugular process.

_Insertion_ into the caudal side of the cartilaginous part of the
stylohyoid opposite the origin of the styloglossus.

_Relations._--Ventral surface with the digastric. Dorsal surface with
the tympanic bulla (3).

_Action._--Draws the hyoid backward and thus gives a firmer surface of
origin for the styloglossus.

=M. mylohyoideus= (Fig. 65, _c_).--The mylohyoid is a large thin muscle
seen after the reflection of the digastric, filling with its fellow of
the opposite side the whole angle between the rami of the lower jaw. Its
fibres are transverse.

_Origin_ from the middle of the medial surface of the body of the
mandible between the caudal opening of the mandibular canal and the
symphysis of the jaw.

  [Illustration: FIG. 67.--MUSCLES OF TONGUE, HYOID BONE, AND PHARYNX.

  _a_, M. tragicus lateralis; _b_, M. jugulohyoideus; _c_, M.
  pterygoideus externus; _d_, partially cut surface of M. pterygoideus
  internus; _e_, M. styloglossus; _f_, M. genioglossus; _g_, M.
  geniohyoideus; _h_, M. hyoglossus; _i_, M. glossopharyngeus; _j_, M.
  constrictor pharyngis medius; _k_, M. constrictor pharyngis inferior;
  _l_, M. stylopharyngeus; _m_, M. sternohyoideus (cut); _n_, M.
  cricothyreoideus; _o_, M. sternothyreoideus (cut); _p_, M.
  thyreohyoideus. 1, mandible; 1′, angular process of mandible; 2,
  stylomandibular ligament; 3, bulla tympani; 4, trachea; 5, œsophagus;
  6, thyroid gland; 7, isthmus of the thyroid gland.]

_Insertion_ with the opposite muscle into a median raphe which extends
from the symphysis of the jaw to the hyoid bone and is closely united to
the external surface of the geniohyoid. Some of the fibres gain
insertion into the body of the hyoid bone through their insertion into
the tendon of the stylohyoid (_d_).

_Relations_.--Outer surface with the submentalis (Fig. 64, _c_) and the
digastric (Fig. 65, _b_). Lateral edge with the masseter (_a_), the
digastric (_b_), and the mandibula. Caudal border with the stylohyoid
(_d_). Inner (dorsal) surface with the geniohyoid (Fig. 67, _g_), the
hyoglossus (Fig. 67, _h_), and the genioglossus (Fig. 67, _f_).

_Action_.--Raises the floor of the mouth and thus brings the hyoid
forward.

=M. ceratohyoideus.=

_Origin_, the two proximal pieces of the cranial horn of the hyoid. The
fibres pass caudad parallel to one another and within the middle
constrictor of the pharynx.

_Insertion_ into the whole length of the caudal cornu of the hyoid bone.

_Relations_.--Outer surface with the middle constrictor of the pharynx.
Inner surface with the pharynx.

_Action_.--Draws craniad the body of the hyoid by bringing its cornua
together and bending the joint between the two pieces of the cranial
cornua.

The muscles connecting the hyoid and the tongue are described in
connection with the description of the tongue.


III. MUSCLES OF THE BODY.


=1. Muscles of the Back.=


A. MUSCLES OF THE SHOULDER (connecting the forelimb with the back) (Fig.
68).

=M. trapezius=.--The trapezius muscle is divided in the cat into three
portions, the spinotrapezius, the acromiotrapezius, and the
clavotrapezius.

=M. spinotrapezius=, or trapezius inferior (Fig. 68, _j_).--The
spinotrapezius (caudal part of the human trapezius) is a flat triangular
muscle.

_Origin_ from the tips of the spinous processes of all or nearly all the
thoracic vertebræ and from the intervening supraspinous ligament. The
origin may extend from a point anywhere between the first and fourth
spines to any point between the eleventh and thirteenth.

_Insertion_ along an S-shaped line (Fig. 76, _k_-_l_) which crosses the
tuberosity of the scapular spine and forms an angle with the spine of
about forty-five degrees. The line extends on one side onto the fascia
covering the supraspinatus muscle, and on the other side onto the fascia
covering the infraspinatus, but does not reach the borders of the
scapula. The cranial two-thirds of the insertion is by a flat tendon
which is broader craniad.

_Relations._--Outer surface with the cutaneus maximus, and craniad with
the acromiotrapezius (_h_). Inner surface with the latissimus dorsi
(_m_) caudad and with the rhomboideus, supraspinatus, and infraspinatus
craniad. Caudal border free; cranial border in contact with the
acromiotrapezius (_h_).

_Action._--Draws the scapula dorsocaudad.

=M. acromiotrapezius=, or trapezius superior (Fig. 68, _h_).--The
acromiotrapezius (middle part of the human trapezius) is a flat
four-sided muscle just craniad of the spinotrapezius, from the median
dorsal line to the scapular spine.

_Origin_ along the median dorsal line from the spinous process of the
axis to a point anywhere between the spinous processes of the first and
fourth thoracic vertebræ. Its caudal two-thirds is from a flat tendon
which is directly continuous with the muscle of the opposite side and
thus bridges the depression between the vertebral borders of the
scapulæ. This tendon narrows craniad, and its cranial fourth is attached
by a fascia to the spinous processes of the cervical vertebræ. At the
cranial border of the muscle the fibres sometimes reach the middle line.
The fibres of the muscle run nearly transversely.

_Insertion_ (Fig. 76, _h_).--Into the outer surface of the metacromion,
the glenoid border of the scapular spine from the metacromion to the
tuberosity, and along a line continued for about one centimeter from the
tuberosity onto the surface of the spinotrapezius (_j_) at the junction
of its muscular and tendinous portions.

  [Illustration: FIG. 68.--FIRST LAYER OF BODY-MUSCLES, BENEATH THE SKIN
  AND SKIN-MUSCLES.

  _a_, M. frontoscutularis; _b_, M. masseter; _c_, M. sternomastoideus;
  _d_, M. clavotrapezius; _e_, M. clavobrachialis; _f_, M. levator
  scapulæ ventralis; _g_, M. acromiodeltoideus; _h_, M.
  acromiotrapezius; _i_, M. spinodeltoideus; _j_, M. spinotrapezius;
  _k_, caput longum of M. triceps brachii; _l_, caput laterale of M.
  triceps brachii; _m_, M. latissimus dorsi; _n_, M. xiphihumeralis;
  _o_, M. pectoralis minor; _p_, M. obliquus abdominis externus; _q_, M.
  sartorius; _r_, M. tensor fasciæ latæ; _s_, M. caudofemoralis; _t_, M.
  biceps femoris; _u_, M. semitendinosus; _v_, M. extensor caudæ
  lateralis; _w_, M. abductor caudæ externus; _x_, M. flexor caudæ
  longus; _y_, lumbodorsal fascia, superficial layer; _z_, fascia lata.
  1, parotid gland; 2, submaxillary gland.]

_Relations._--Outer surface with the cutaneus maximus, the integument
and platysma. Inner surface with a mass of fat partially covering the
rhomboideus; with the occipitoscapularis, spinotrapezius, supraspinatus,
levator scapulæ, and splenius. Near its origin its caudal border touches
the outer surface of the spinotrapezius (_j_). Its cranial border is
overlaid near its insertion by the levator scapulæ ventralis (_f_) and
is closely related to the caudal border of the clavotrapezius (_d_)
near its origin.

_Action._--The two muscles hold the scapulæ together.

=M. clavotrapezius= (Fig. 68, _d_).--The clavotrapezius (cranial part of
the human trapezius) is a flat muscle passing from the lambdoidal crest
and middorsal line to the clavicle and covering the side of the neck.

_Origin._--The medial half of the lambdoidal crest and the middorsal
line between the crest and the caudal end of the spine of the axis. The
fibres are parallel and pass caudoventrad so that the muscle covers the
ventral surface of the neck caudally and fills the concavity at the
front of the shoulder.

_Insertion_ into the clavicle and into a raphe between the
clavotrapezius and the clavobrachial (_e_) muscles. This raphe extends
along the clavicle and for some distance laterad of it. The muscle is
partly continuous with the clavobrachial (_e_).

_Relations._--Outer surface with the platysma, and at its craniomedial
angle with the levator auris longus. Inner surface with the rhomboideus,
splenius, occipitoscapularis, levator scapulæ, cleidomastoid, and
supraspinatus. The cranial edge touches the sternomastoid. The caudal
border touches the acromiotrapezius near the origin.

_Action._--Draws the scapula craniodorsad.

This muscle and the clavobrachial (_e_) are sometimes considered as
forming a single muscle, the cephalohumeral, or cephalobrachial.

=M. occipitoscapularis= (or levator scapulæ dorsalis or rhomboideus
capitis) (Fig. 73, _a_).--The occipitoscapularis (equivalent to a part
of the human rhomboideus) is a slender flat muscle from the lambdoidal
ridge to the coracovertebral angle of the scapula.

_Origin_, the medial half of the lambdoidal ridge beneath the
clavotrapezius (Fig. 68, _d_). The origin does not extend quite to the
middle line. The muscle passes almost directly caudad. Its caudal end is
thicker and narrower than the cranial end and is wedged between the
rhomboideus dorsally and the levator scapulæ ventrally.

_Insertion_ either into the inner surface of the levator scapulæ near
its dorsocranial border at its insertion or into the scapula near the
coracovertebral angle (Fig. 78, _f_) or into both. Its fibres are very
closely related to those of the rhomboideus.

_Relations._--By its outer surface with the clavotrapezius (Fig. 68,
_d_) and acromiotrapezius (_h_). At its insertion it is often overlaid
by either the rhomboideus or the levator scapulæ or both. By its inner
surface with the splenius (Fig. 73, _b_). Its caudal third is wedged
between the rhomboideus and the levator scapulæ.

_Action._--Draws forward and rotates the scapula.

=M. rhomboideus= (probably equivalent to the human rhomboideus major and
rhomboideus minor).--A rather thick trapezoid muscle connecting the
vertebral border of the scapula with the spinous processes of the
adjacent vertebræ.

_Origin_ from the caudal two or three fifths of the cervical
supraspinous ligament and from the sides and tips of the first four
thoracic vertebral spines and the interspinous ligaments caudad of these
four spines. It passes lateroventrad, and the fibres converge somewhat
so that the line of insertion is shorter than the line of origin.

_Insertion_ by a short tendon (1 millimeter long) into the vertebral
border of the scapula, the line of insertion passing gradually from the
inner (Fig. 78, _e_) to the outer (Fig. 76, _i_) surface; and by fleshy
fibres into the outer surface of the glenovertebral angle of the scapula
(Fig. 76, _i_) in close connection with the origin of the teres major
(_j_). A bundle of fibres at the cranial border may be inserted into the
cranial border of the levator scapulæ at its insertion.

_Relations._--By its outer surface with the spinotrapezius (Fig. 68,
_j_), acromiotrapezius (_h_), latissimus dorsi (_m_), and clavotrapezius
(_d_); it is usually partially separated from these muscles by a mass of
fat. By its inner surface near its insertion with the serratus anterior
(Fig. 73, _i_) and levator scapulæ (Fig. 73, _h_), and craniad with the
splenius (Fig. 73, _b_), and the tendon of the serratus posterior
superior (Fig. 73, _l_). At its lateral end it touches the
occipitoscapularis (Fig. 73, _a_), serratus anterior (_i_), levator
scapulæ (_h_), supraspinatus (Fig. 75, _a_), and infraspinatus (Fig. 75,
_c_), and the teres major (Fig. 75, _d_).

_Action._--Draws the scapula toward the vertebral column.

=M. cleidomastoideus= (clavicular portion of the human
sternocleidomastoid) (Fig. 65, _h_).--A narrow flat muscle between the
mastoid process and the clavicle.

_Origin_ from the apex and caudal margin of the mastoid process of the
temporal bone, by tendon and muscle fibres. The muscle passes caudad,
becoming broader and thinner.

_Insertion_ into the lateral four-fifths of the clavicle within the
insertion of the clavotrapezius, and into the raphe which continues
laterad of the clavicle.

_Relations._--Outer or lateral surface at the caudal end with the
clavotrapezius (Fig. 65, _j_); further craniad with the depressor conchæ
(Fig. 64, _b_), the platysma, and the sternomastoid (Fig. 65, _g_).
Inner or medial surface with the supraspinatus (Fig. 75, _a_) caudad,
with the mass of fat in the axilla at its middle, with the levator
claviculæ ventralis (Fig. 65, _i_) and obliquus capitis superior (Fig.
71, _e_) craniad.

_Action._--Pulls the clavicle craniad when the head is fixed. Turns the
head and depresses the snout when the clavicle is fixed.

=M. levator scapulæ ventralis=, or levator claviculæ (Fig. 68, _f_; Fig.
65, _i_; Fig. 72, _c_, _c′_, _c″_) (not usually found in man).

_Origin_ (Fig. 72, _c′_, _c″_) in two parts. (1) By fleshy fibres from
the ventral surface of the atlantal transverse process near its caudal
border (_c′_). (2) By a small tendon from the ventral surface of the
basioccipital opposite the middle of the length of the bulla tympani
(_c″_) in common with the longus capitis (_a_). The two heads unite to
form a flat band which passes caudoventrad and is inserted (Fig. 76,
_f_) by a flat short tendon, about eight millimeters broad, into the
outer surface of the metacromion along its ventral border, and into the
infraspinatus fossa for one or two millimeters distad of that border.

_Relations._--Near the insertion the dorsal border overlaps the border
of the acromiotrapezius (Fig. 68, _h_), and the ventral border is
attached by strong fascia to the border of the clavotrapezius (Fig. 68,
_d_). The outer surface is in relation with the longissimus capitis
(Fig. 73, _g_), clavotrapezius (Fig. 68, _d_), cleidomastoid (Fig. 73,
_d_), platysma, and the skin. The inner surface is in relation caudad
with the supraspinatus and with a mass of fat and a lymphatic gland
which occupy the hollow of the shoulder. Craniad it is in relation with
the cleidomastoid (Fig. 73, _d_), the scalenus (Fig. 73, _f_), the
longus capitis (Fig. 73, _e_), and the obliquus superior (Fig. 71, _e_).

_Action._--Pulls the scapula craniad.

=M. latissimus dorsi= (Fig. 68, _m_; Fig. 65, _q_; Fig. 77, _e_).--A
large triangular sheet covering rather more than the dorsocranial half
of the abdomen and thorax. It arises from the middorsal line, from the
pelvis to the fifth thoracic spine, and is inserted into the humerus.

_Origin_ from the tips of the neural spines of the vertebræ from the
fourth or fifth thoracic to about the sixth lumbar. As far as the tenth
or eleventh thoracic vertebra the origin is directly by muscle-fibres.
Caudad of this is a broad triangular tendon which may be so closely
united to the tendons of the underlying muscles that it cannot be
separated. The muscle passes cranioventrad, the fibres converging to the
axilla. In the axilla a part of the cutaneus maximus and the
epitrochlearis (Fig. 65, _r_) take origin from the outer surface.

_Insertion._--The muscle then ends in a flat tendon, to the cranial
surface of which the fibres of the teres major (Fig. 77, _c_) are
attached. Five to ten millimeters from the humerus the muscle-fibres of
the teres give place to the tendon-fibres, and the conjoined tendon of
the teres and latissimus which is thus formed (Fig. 79, _d′_) is
inserted into a rough elongated area (Fig. 82, _f_) which lies parallel
with the pectoral ridge on the medial surface of the shaft of the
humerus (Fig. 48, _g_). The teres tendon forms the proximal part of the
conjoined tendon. A part of the tendon of the latissimus may join the
pectoralis minor at its distal or caudal border (Fig. 65), and thus it
may contribute to the formation of both pillars of the bicipital arch
(Fig. 65, _t′_).

_Relations._--Its outer surface is covered caudad by the cutaneus
maximus, and craniad by the spinotrapezius (Fig. 68, _j_) and the long
head of the triceps (Fig. 68, _k_). The cranial border comes into
relation with the spinotrapezius (j) and teres major (Fig. 77, _c_).
The caudal border is in contact at the ventral end with the
xiphihumeralis (Fig. 65, _p_) and pectoralis minor (Fig. 65, _o_). The
inner surface of the latissimus covers near its cranioventral end parts
of the xiphihumeralis (Fig. 68, _n_), pectoralis minor (Fig. 68, _o_),
teres major (Fig. 77, _c_), and serratus anterior (Fig. 73, _i_). The
caudal border covers a portion of the obliquus externus abdominis (Fig.
68, _p_); the dorsal and middle portions cover parts of the longissimus
dorsi (Fig. 69, _f″_), the spinalis dorsi (Fig. 69, _g_), the serratus
posterior superior (Fig. 73, _l_), and serratus posterior inferior (Fig.
73, _n_).

_Action._--Pulls the arm caudodorsad.

=M. serratus anterior= and =levator scapulæ= (Fig. 73, _i_ and _h_) in
the cat are continuous at both origin and insertion, and it is barely
possible to separate their contiguous borders without cutting the
fibres. The muscle extends from the transverse processes of the last
five cervical vertebræ and from the first nine or ten ribs to the medial
surface of the scapula near its vertebral margin (Fig. 78, _c_ and _d_).

=M. serratus anterior= (or serratus magnus) (Fig. 73, _i_).

_Origin._--From the first nine or ten ribs in as many subdivisions. The
first subdivision arises from the whole or nearly the whole of the
caudal border of the first rib. The next four or five arise either from
the ribs or from the costal cartilages near or at their junction with
the ribs. The last four subdivisions arise from the ribs at increasing
distances from the cartilages. The fibres converge and the subdivisions
join one another.

_Insertion_ (Fig. 78, _c_) into a narrow area on the medial surface of
the scapula near the vertebral border. The glenoid half of the insertion
is by a short tendon, the remainder by muscle-fibres.

_Relations._--Outer (lateral) surface with the latissimus dorsi (Fig.
68, _m_), teres major (Fig. 77, _c_), subscapularis (Fig. 77, _a_), and
near the origin with the rectus abdominis (Fig. 73, _k_), the scalenus
(Fig. 73, _f_-_f‴_), and the obliquus externus (Fig. 68, _p_). Inner
(medial) surface with the serratus posterior superior (Fig. 73, _l_) and
its tendon, and with the intercostales externi (Fig. 73, _m_). At its
insertion the muscle touches the rhomboideus. The cranial edge is united
to the caudal edge of the levator scapulæ (Fig. 73, _h_).

_Action._--Depressor of the scapula.

=M. levator scapulæ= (Fig. 73, _h_).

_Origin._--From the dorsal tubercles of the transverse processes of the
last five cervical vertebræ and from the ligaments between the
tubercles. A slip sometimes arises from the atlas.

_Insertion_ (Fig. 78, _d_) into a triangular area on the medial surface
of the scapula near its vertebral border. It is continuous with the
insertion of the serratus anterior.

_Relations._--Outer (lateral) surface with a mass of fat separating it
from the clavotrapezius (Fig. 68, _d_) and cleidomastoid (Fig. 65, _h_),
and with the subscapularis (Fig. 77, _a_). Inner (medial) surface with
the splenius (Fig. 73, _b_), the tendon of the serratus posterior
superior (Fig. 73, _l_), and the cervical portion of the longissimus
dorsi (Fig. 69, _f″_). Near the insertion the muscle touches the
occipitoscapularis (Fig. 73, _a_) and rhomboideus. Caudal border united
with the serratus anterior (Fig. 73, _i_).

_Action._--Draws the scapula cranioventrad.


B. MUSCLES OF THE BACK (interconnecting parts of the vertebral column)
(Fig. 69).--The muscles connected with the vertebral column form a mass
which is less markedly differentiated into distinct muscles than is the
case in the limbs. A great longitudinal mass of fibres begins in the
sacral region and extends along the vertebral column to the head. This
mass contains fibres running in various directions and attached at one
or both ends to the sacrum, the innominate bones, the spinous,
transverse, and articular processes, and to the arches, of the vertebræ;
to the ribs and to the head, and having in general the function of
moving the vertebræ in various ways, or of moving parts connected with
the vertebræ. In some regions, especially the cervical, it is possible
to distinguish clearly distinct muscles which have been differentiated
from this mass. In the greater part of its extent, however, it is
possible to distinguish only more or less closely interconnected
bundles,--the more clearly marked of which have received special names.

The great dorsal mass running along each side of the vertebral column,
occupying the space between the spinous processes and the transverse
processes, receives the general name of =M. extensor dorsi communis=;
the separate muscles are to be considered as parts or differentiations
of this. The largest part of the mass is in the lumbar region (first
portion of the =longissimus dorsi=, Fig. 69, _f_). At the caudal end of
the thorax a lateral mass, parts of which become connected with the
ribs, is separated off from the main part of the muscle; this extends
craniad into the cervical region as =M. iliocostalis= (_h_). The main
portion of the longissimus dorsi (_f′_) continues craniad on the medial
side of the iliocostal into the neck region. At about the level of the
eighth or ninth thoracic vertebra a strip begins to become separated off
on the medial side of the longissimus; further forward it becomes
clearly distinct, forming the =spinalis dorsi= (_g_). The separate
muscles connecting the cervical vertebræ with each other and with the
head are differentiations of the extensor dorsi communis.

A still deeper set of fibres, interconnecting the vertebræ, forms the
=multifidus spinæ= and a number of other small muscles.

A description of the different bundles of fibres, under the names
usually given, follows. Certain general principles are observed in some
of the names used. Muscles which interconnect the spinous processes of
the vertebræ receive the name =spinalis.= Those interconnecting
contiguous spinous processes are called =interspinalis.= Muscles
attached at one end to transverse processes, at the other to the spinous
processes, receive the name =transversospinalis=. =Semispinalis= has the
same signification as transversospinalis, but is a name usually
applied to subdivisions of the transversospinalis group. The
=intertransversarii= are muscles interconnecting the transverse
processes.

  [Illustration: FIG. 69.--DEEP MUSCLES OF BODY, EXPOSED AFTER REMOVAL
  OF THE MUSCLES SHOWN IN FIG. 73.

  _a_, M. biventer cervicis; _b_, M. complexus; _c_, M. obliquus capitis
  superior; _d_, M. longus atlantis; _e_, cut end of M. longissimus
  capitis; _f_, _f′_, _f″_, M. longissimus dorsi; _g_, M. spinalis
  dorsi; _h_, M. iliocostalis; _i_, Mm. intercostales externi; _k_, Mm.
  intercostales interni; _l_, M. transversus abdominis.]


(_a_) _Muscles of the Lumbar and Thoracic Regions._--The muscles of the
lumbar and thoracic regions are mostly covered by a strong fascia, known
as the =lumbodorsal= fascia (Fig. 68, _y_). This consists of two sheets,
the superficial sheet being applied directly to the outer surface of the
inner sheet, or separated from it by a mass of fat.

The superficial sheet (Fig. 68, _y_) overlies the lumbar region and the
caudal half of the thoracic region. On the medial side it is attached to
the spinous processes of the vertebræ and is united closely to the
deeper layer. Laterally this fascia is continuous with the latissimus
dorsi (_m_) and obliquus abdominis externus (_p_). Caudad it is attached
to the spine of the ilium and becomes continuous with the fascia
covering the gluteus muscles.

The deeper sheet (Fig. 70, _c_) is of a tendinous character, forming the
external tendinous layer of the longissimus dorsi, many of whose fibres
take origin from its under surface. It is described more fully in the
account of this muscle.

=M. longissimus dorsi= (Fig. 69, _f_, _f′_, _f″_; Fig. 70, _a_ and
_b_).--A very large muscle, filling most of the region between the
spinous processes and transverse processes of the lumbar and thoracic
vertebræ, and extending into the cervical region.

The muscle is largest in the lumbar region (Fig. 69, _f_; Fig. 70),
where it is divided into a narrow medial (Fig. 70, _a_) and a thick
lateral portion (Fig. 70, _b_), the latter being again partially
subdivided by the fascia. The two parts unite farther craniad.

The =medial division= (Fig. 70, _a_) consists of muscular bundles
connecting the spinous processes of the vertebræ with the accessory and
mammillary processes of other vertebræ; it is continuous caudad with the
extensor caudæ lateralis (Fig. 70, _f_). The muscle-fibres take origin
in the sacral region by small round tendons from the spinous processes
of the last two sacral and the caudal vertebræ. They curve
cranioventrad, forming a large belly, and are inserted into the
accessory and mammillary processes of the lumbar vertebræ. In the
thoracic region this division unites with that portion of the lateral
division in which the fibres coming from the fascia of origin are
inserted into the laminæ and transverse processes of the thoracic
vertebræ.

The =lateral division= (Fig. 70, _b_) is much larger than the medial
one, forming in the lumbar region a nearly cylindrical mass.

  [Illustration: FIG. 70.--MUSCLES ON THE DORSAL SIDE OF THE VERTEBRAL
  COLUMN IN THE LUMBAR, SACRAL, AND CAUDAL REGIONS.

  Both sheets of the lumbodorsal fascia have been removed, the deep
  layer (_c_) being cut where it passes into the longissimus dorsi. 1,
  crest of ilium; 4-7, tips of spinous processes of the fourth to
  seventh lumbar vertebræ. _I_, _II_, tips of spinous processes of first
  two sacral vertebræ. _a_, _b_, M. longissimi dorsi (_a_, medial
  portion; _b_, lateral portion; _b′_, portion taking origin from the
  lumbodorsal fascia); _c_, cut edge of deep layer of lumbodorsal
  fascia; _d_, M. multifidus spinæ; _e_, M. extensor caudæ medialis;
  _f_, M. extensor caudæ lateralis, _g_, M. abductor caudæ externus.]

_Origin_ from the crest of the ilium (Fig. 70, 1) and the medial surface
of the ilium as far caudad as the auricular impression; also from the
deep layer of the lumbodorsal fascia (_c_). This fascia is connected
with the crest of the ilium and with the tips of the spinous processes
of the vertebræ in the lumbar and thoracic regions, and from it a large
proportion of the fibres of the longissimus take origin. In the lumbar
region it dips into the muscle as an intermediate longitudinal sheet
(_c_), partially dividing it lengthwise into two parts. Fibres taking
origin from the lateral surface of this intermediate sheet curve
cranioventrad, and are inserted on the transverse processes of the
lumbar vertebræ. Fibres taking origin from the medial surface of the
sheet pass mediocraniad and are inserted into the accessory processes
and the surfaces of the vertebral arches. In the thoracic region (Fig.
69, _f′_) most of the fibres are inserted in separate bundles by small
tendons on the transverse processes of the vertebræ, while some of the
medial fibres unite with tendinous strands which become attached to the
laminæ and articular processes of the vertebræ. At the region of the
eighth or ninth thoracic vertebra the =spinalis dorsi= (Fig. 69, _g_)
begins to be separated off on the medial side, the separation becoming
complete only some distance farther craniad; the longissimus dorsi then
continues into the cervical region (_f″_). Bundles of fibres become
attached in the manner above described to transverse processes of all
the thoracic vertebræ. In the cervical region (_f″_) the muscle spreads
out and becomes thinner, and bundles of fibres become attached to the
transverse processes of the cervical vertebræ as far forward as the
second. In the more cranial portion of its extent the muscle receives
fibres having origin on the articular processes and laminæ of the
cervical and a few of the more cranial thoracic vertebræ.

The portion of the muscle which is inserted on the cervical transverse
processes (_f″_) is sometimes distinguished as the =longissimus
cervicis=; it is not well separated from the rest of the muscle in the
cat. The =longissimus capitis= (Fig. 69, _c_; Fig. 73, _g_) is to be
considered a differentiated cranial portion of this muscle.

_Relations._--Outer surface with the following, beginning with the
caudal end: the sartorius (Fig. 68, _q_), the latissimus dorsi (Fig. 68,
_m_), the lumbodorsal fascia (Fig. 68, _y_), the serratus posterior
inferior (Fig. 73, _n_) and superior (Fig. 73, _l_), and the levator
scapulæ (Fig. 73, _h_). Lateral margin with the abdominal muscles, the
iliocostal (Fig. 69, _h_), and the levator scapulæ (Fig. 73, _h_).
Medial side with the multifidus spinæ (Fig. 70, _d_), the spinous
processes of the thoracic vertebræ, the spinalis dorsi (Fig. 69, _g_),
the complexus (Fig. 69, _b_), the biventer cervicis (Fig. 69, _a_), and
the longissimus capitis (Fig. 69, _e_).

_Action._--Extends the vertebral column.

=M. iliocostalis= (Fig. 69, _h_).--This is a muscle about 1½ to 2
centimeters wide, lying on the dorsal portion of the ribs, laterad of
the longissimus dorsi (_f′_). It is composed of many partly separated
bundles, each with an oblique tendon. The muscle begins at the last or
next to the last rib, where it is connected with the longissimus by a
rather small bundle of fibres. The rest of the muscle-fibres take origin
in bundles from the lateral surface of the ribs, at about the angles, or
from thin tendons connecting the angles, of the ribs; they pass
obliquely craniad and are inserted, usually by tendons, on the lateral
surface of the third or fourth rib craniad of the one on which the given
bundle has origin. The insertions on any given rib lie ventrad of the
origins on the same rib. In the cat this muscle is confined to the
thoracic region.

_Relations._--Outer surface with the serratus posterior inferior (Fig.
73, _n_) and superior (Fig. 73, _l_), and the levator scapulæ (Fig. 73,
_h_). Inner surface with the dorsal surface of the ribs, the external
intercostals (Fig. 69, _i_), and craniad with the levatores costarum.
Medial edge in contact with the longissimus dorsi (Fig. 69, _f′_).

_Action._--Draws the ribs together.

=M. spinalis dorsi= (Fig. 69, _g_).--A muscle interconnecting the
spinous processes of vertebræ some distance apart, in the thoracic and
cervical regions. It lies on the medial side of the longissimus dorsi
(_f′_).

_Origin_ by strong tendons from the tips of the spinous processes of the
tenth to the thirteenth thoracic vertebræ. These tendons represent the
cranial portion of the deep layer of the lumbodorsal fascia, and give
origin also to many fibres of the longissimus dorsi, so that the two
muscles are completely united at the origin of the spinalis. They become
separated at about the level of the sixth thoracic vertebra, the
spinalis forming a strong separate bundle passing into the neck region
close against the sides of the spinous processes. The insertion is by
fleshy bundles into the sides of the spinous processes of the first nine
or ten thoracic vertebræ and of the cervical vertebræ as far forward as
the second. Some of the fibres of this muscle pass craniad into the
biventer cervicis (Fig. 69, _a_).

_Relations._--Outer surface with the tendons of the serratus posterior
inferior (Fig. 73, _n_) and serratus posterior superior (Fig. 73, _l_),
and with the splenius (Fig. 73, _b_), biventer cervicis (Fig. 69, _a_),
and complexus (Fig. 69, _b_). Lateral and ventral surface with the
longissimus dorsi (_f′_); medial surface with the spinous processes and
the multifidus spinæ.

_Action._--Extensor of the vertebral column.

=M. multifidus spinæ=.--This consists of bundles of fibres which have
origin on the transverse processes or neighboring parts, pass
craniodorsad across one or more vertebræ, and are inserted into the
spinous processes of vertebræ lying some distance craniad of the origin.
They lie deeper than the muscles previously described. The muscle is
most strongly developed in the lumbar region (Fig. 70, _d_), where it
forms a thick interwoven mass in which it is difficult to distinguish
separate bundles. The fibres in this region have origin on the accessory
or mammillary processes and usually pass over more than one vertebra
between origin and insertion; their insertions reach the dorsal ends of
the spinous processes, so that part of the muscle lies immediately
beneath the lumbar fascia. In other regions the multifidus is covered by
other muscles. In the thoracic region the separate bands are more
distinct, and usually pass in their course over but one intervening
vertebra. In the cervical region the bands are interconnected, forming a
fairly distinct single muscle, which is described separately below as
the =semispinalis cervicis= (Fig. 71, _c_). The portion of this muscle
attached to the head (=semispinalis capitis=) forms the biventer
cervicis (Fig. 69, _a_) and complexus (_b_). Caudad this muscle passes
onto the tail as the =extensor caudæ medialis= (Fig. 70, _c_).

_Relations._--Outer and lateral surface in the lumbar region with the
longissimus dorsi (Fig. 69, _f_) and the lumbodorsal fascia (Fig. 68,
_y_); in the thoracic region with the longissimus dorsi (Fig. 69, _f′_)
and spinalis dorsi (_g_). Inner surface with the arches, articular
processes, and spinous processes of the vertebræ.

_Action._--Extends the back when the muscles of both sides work
together. Turns the vertebral column obliquely sideways when one set
acts alone.

The deepest layer of the multifidus forms what is sometimes
distinguished as the =Mm. rotatores=; no separate layer of this sort is
to be made out in the cat.

=Mm. interspinales.=--Muscle-bundles passing from the spinous process of
one vertebra to that of the vertebra immediately craniad or caudad of
it. They are best developed in the lumbar region.

=Mm. intertransversarii.=--Muscle-fibres interconnecting the transverse
processes. In the lumbar region the =intertransversarii mediales=
connect the accessory and mammillary processes; the =intertransversarii
laterales= lying between the transverse processes. In other regions only
one set of the intertransversarii is to be distinguished.


(_b_) _Dorsal Muscles of the Cervical Region._--The clavotrapezius (Fig.
68, _d_) and occipitoscapularis (Fig. 73, _a_) have been described in
connection with the muscles of the shoulder. The remaining muscles of
this region may be considered as differentiations of the general
vertebral musculature (M. extensor dorsi communis).

=M. splenius= (Fig. 73, _b_.)--A large sheet of muscle covering the
dorsal part of the side of the neck, beneath the trapezii.

_Origin_ from the whole cervical ligament and from the fascia covering
the deeper muscles along a line which extends from the first thoracic
spinous process caudolaterad for about two centimeters.

_Insertion_ by a thin tendon into the whole lambdoidal ridge. Laterad
the tendon may be fused with that of the longissimus capitis (Fig. 73,
_g_).

_Relations._--Outer surface with the sternomastoid (Fig. 68, _c_),
occipitoscapularis (Fig. 73, _a_), clavotrapezius (Fig. 68, _d_),
rhomboideus, tendon of the serratus posterior superior (Fig. 73, _l_),
and the levator scapulæ (Fig. 73, _h_). Lateral edge closely united with
the longissimus capitis (Fig. 73, _g_). Inner surface with the
longissimus capitis, complexus (Fig. 69, _b_), and biventer cervicis
(Fig. 69, _a_).

_Action._--Lateral flexor of the head. The two together elevate the
head.

=M. longissimus capitis= (=trachelomastoideus=) (Fig. 73, _g_; Fig. 69,
_e_).--This is a slender muscle lying close against the lateral border
of the splenius (Fig. 73, _b_), and sometimes fused with the splenius at
its craniad end. It is a cranial continuation of the longissimus dorsi
(Fig. 69, _f″_).

_Origin_ by five slips which are attached by strong tendons to the
anterior articular processes of the last four cervical vertebræ. The
tendons are common to this muscle and the complexus. The five slips
unite to form a flat belly which has its

_Insertion_ by a strong rounded tendon into the mastoid process of the
temporal bone. The tendon may be closely united to that of the splenius.

_Relations._--Lateral surface with the sternomastoid (Fig. 68, _c_), the
levator scapulæ (Fig. 73, _h_), and longissimus dorsi (Fig. 69, _f″_).
Medial surface with the splenius (Fig. 73, _b_) (to which it is partly
united), the complexus (Fig. 69, _b_), and the longus atlantis (Fig. 69,
_d_).

_Action._--Lateral flexor of the head.

=M. biventer cervicis= (Fig. 69, _a_) (=medial portion of M.
semispinalis cervicis et capitis=).--The biventer cervicis is a flat
muscle which lies beneath the splenius (Fig. 73, _b_), next the median
line of the neck, with its fibres longitudinal.

_Origin_ in three or four slips from the surface of the three or four
aponeurotic arches which take origin from the tips of the spinous
processes of the last cervical and the first three thoracic vertebræ and
pass laterad and caudad to the anterior processes of the second, third,
fourth, and fifth thoracic vertebræ. These arches are deviated from
their straight course by four aponeurotic bands which pass from them
obliquely caudad and dorsad to the sides of the spinous processes of the
vertebræ into which the arches are inserted. The arches form the
beginning of the sheet of fascia which passes outside of the
longitudinal supraspinous muscles, and the anchoring bands form the
beginning of a similar sheet which passes within the longitudinal
supraspinous muscles. An additional slip may take origin from the
cervical ligament between the last cervical and the first thoracic
vertebræ. The fibres form a flat band divided by two or three oblique
tendinous intersections. It adheres closely to the cervical supraspinous
ligament.

_Insertion_ by a strong tendon into the medial part of the lambdoidal
crest.

_Relations._--Outer surface with the splenius (Fig. 73, _b_) and at the
caudal end with the longissimus dorsi (Fig. 69, _f″_). Inner surface
with the spinalis dorsi (Fig. 69, _g_), the semispinalis cervicis (Fig.
71, _c_), and the rectus capitis posterior major (Fig. 71, _a_). Medial
edge with the muscle of the opposite side; lateral edge with the
complexus (Fig. 69, _b_).

_Action._--Raises the snout.

=M. complexus= (Fig. 69, _b_) (=lateral portion of M. semispinalis
cervicis et capitis=).--The complexus is closely associated with the
biventer cervicis (_a_) and lies on its lateral side beneath the
splenius (Fig. 73, _b_).

_Origin_ by tendinous bands from the anterior articular processes of the
last five or six cervical and the first one, two, or three thoracic
vertebræ. The same bands give origin externally to the fibres of the
longissimus capitis (Fig. 69, _e_), and internally to those of deeper
muscles of the neck. The six or more muscular slips continued from these
tendons unite to form a flat band, the

_Insertion_ of which is by a flat tendon into the medial third of the
lambdoidal crest some distance ventrad of the free edge of the crest.
Near the insertion the lateral border of the muscle is connected by an
aponeurotic band to the lateral border of the transverse process of the
atlas.

_Relations._--Outer surface at the dorsal border with the biventer
cervicis (Fig. 69, _a_); at the middle with the splenius (Fig. 73, _b_);
at the ventral border with the longissimus capitis (Fig. 69, _e_) and
the longissimus dorsi (Fig. 69, _f″_). Inner surface with the cervical
portion of the spinalis dorsi, with the semispinalis cervicis (Fig. 71,
_c_), the obliquus capitis inferior (Fig. 71, _b_), the rectus capitis
posterior major (Fig. 71, _a_), and the obliquus superior (Fig. 71,
_e_).

_Action._--Raises the head.

=M. spinalis dorsi= extends into the cervical region; it has been
described.

=M. semispinalis cervicis= (Fig. 71, _c_).--This represents that portion
of the multifidus spinæ which extends into the cervical region. It is
not composed of distinct bundles, like the multifidus of the thoracic
region, but all the fibres are united into a fairly well-defined muscle.

_Origin_ from the articular processes of the last five cervical
vertebræ.

_Insertion_ into the spinous processes of the cervical vertebræ up to
the second, the largest part of the muscle being inserted into the
caudal end of the spine of the atlas.

_Relations._--Outer surface with the spinalis dorsi (Fig. 69, _g_) and
the complexus (Fig. 69, _b_). Inner surface with the vertebræ.

_Action._--Extends the neck.

=M. longissimus dorsi= extends into the cervical region, where it is
often distinguished as the =longissimus cervicis= (Fig. 69, _f″_). It
has been described.

=M. longus atlantis= (Fig. 71, _f_; Fig. 69, _d_).--This represents a
differentiated portion of the longissimus dorsi.

_Origin_ from the transverse process and the side of the vertebral arch
of the third cervical vertebra.

_Insertion_ into the caudolateral angle of the wing of the atlas.

_Relations._--Dorsal surface with the complexus (Fig. 69, _b_), the
longissimus capitis (Fig. 69, _e_), and the obliquus inferior (Fig. 71,
_b_). Ventral surface with the scalenus (Fig. 71, _g_), longissimus
dorsi (Fig. 69, _f″_), and levator scapulæ (Fig. 71, _h_).

_Action._--Extends the neck and turns the head sideways.

=M. rectus capitis posterior major= (Fig. 71, _a_).

_Origin._--The whole length of the spinous process (or crest) of the
axis, or its caudal part only. It is united by a raphe to the opposite
muscle. The muscle passes craniad and laterad to its

_Insertion_ into an area ventrad of the medial part of the lambdoidal
crest beneath the insertion of the complexus (Fig. 69, _b_) and the
biventer cervicis (Fig. 69, _a_).

_Relations._--Dorsal surface with the biventer cervicis (Fig. 69, _a_).
Ventral surface with the rectus capitis posterior medius (Fig. 71, _d_)
and the obliquus capitis inferior.

_Action._--Raises the snout.

=M. rectus capitis posterior medius= (Fig. 71, _d_). (This is in man a
part of the rectus capitis posterior major.)--It lies beneath the rectus
capitis posterior major (Fig. 71, _a_).

  [Illustration: FIG. 71.--DEEP MUSCLES OF THE NECK, AFTER THE REMOVAL
  OF MM. BIVENTER CERVICIS AND COMPLEXUS.

  _a_, M. rectus capitis posterior major; _b_, M. obliquus capitis
  inferior; _c_, M. semispinalis cervicis; _d_, M. rectus capitis
  posterior medius; _e_, M. obliquus capitis superior; _f_, M. longus
  atlantis; _g_, M. scalenus (part of cervical portion); _h_, cut end of
  M. levator scapulæ.]

_Origin_ from the cranial end of the axial spine. It forms a triangular
prismatic mass which passes craniad and has its

_Insertion_ into an elongated area on the occipital bone, ventrad of the
median half of the lambdoidal crest.

_Relations._--Dorsal surface with the rectus capitis posterior major
(Fig. 71, _a_). Ventral surface with the atlas and the rectus capitis
posterior minor.

_Action._--Assists the rectus capitis posterior major.

=M. rectus capitis posterior minor.=--A small triangular muscle beneath
the rectus capitis posterior medius (Fig. 71, _d_).

_Origin_ by the apex of the triangle from the cranial border of the
dorsal arch of the atlas for about two millimeters laterad of the median
line. The muscle passes over the ligament which connects the atlas to
the occiput and adheres to it.

_Insertion_ into an elongated area on the occipital bone, ventrad of the
insertion of the rectus capitis posterior medius for about five
millimeters next to the median line.

_Relations._--Dorsal surface with the rectus capitis posterior medius.
Ventral surface with the posterior atlanto-occipital membrane.

_Action._--Assists the rectus capitis posterior major.

=M. obliquus inferior= (Fig. 71, _b_).

_Origin_ from the whole lateral surface of the spine of the axis. The
parallel fibres form a thick mass which passes laterad and craniad.

_Insertion_ into the dorsal surface of the transverse process of the
atlas along a narrow area near its lateral margin.

_Relations._--Outer surface with the rectus capitis posterior major
(Fig. 71, _a_), the complexus (Fig. 69, _b_), and the obliquus superior
(Fig. 71, _e_). Inner surface with the axis.

_Action._--Rotates the head.

=M. obliquus capitis superior= (Fig. 71, _e_; Fig. 72, _e_).--This is a
triangular muscle passing from the outer border of the atlas laterad of
the recti capitis posteriores to the occiput.

_Origin_ from the lateral border of the transverse process of the atlas
on its ventral margin. The fibres pass craniad and diverge.

_Insertion_ into the caudal side of the mastoid process of the temporal
bone and into a line parallel with the lambdoidal ridge and ventrad of
it, from the mastoid process to within one centimeter of the median
line.

_Relations._--Outer surface with the splenius (Fig. 73, _b_), complexus
(Fig. 69, _b_), and longissimus capitis (Fig. 73, _g_). Inner surface
with the obliquus inferior (Fig. 71, _b_), the wing of the atlas, and
the rectus lateralis (Fig. 72, _d_). Ventral border with the
cleidomastoid (Fig. 73, _d_) and one head of the levator scapulæ
ventralis (Fig. 72, _c′_).

_Action._--Flexes the head laterally.

=Mm. interspinales= and =intertransversarii= are found in the neck
region also; they are described with the muscles of the back.


C. MUSCLES OF THE TAIL.--=M. extensor caudæ medialis= (Fig. 70,
_e_).--This is a continuation caudad of the multifidus spinæ (Fig. 70,
_d_); it lies next to the dorsal median line, the muscles of right and
left side touching one another in the middle line.

_Origin_ by numerous fleshy bundles from the spinous processes of the
sacral and first caudal vertebræ. The fibres pass caudad and are
inserted by tendons into the articular processes and the dorsal surface
of the caudal vertebræ.

_Action._--Extends (raises) the tail.

=M. extensor caudæ lateralis= (Fig. 70, _f_).--This is a continuation
caudad of the medial portion of the longissimus dorsi (Fig. 70, _a_); it
lies just laterad of the extensor caudæ medialis (Fig. 70, _e_).

_Origin_ in many fleshy bundles from the articular processes of the
sacral vertebræ, and the transverse processes of the caudal vertebræ.
The fibres curve dorsocaudad and are inserted by many long slender
tendons on the dorsal surfaces of the caudal vertebræ. The muscle grows
continually smaller as it passes caudad.

_Action._--Raises the tail.

=M. abductor caudæ= (coccygis) =externus= (Fig. 68, _w_; Fig. 70,
_g_).--A rounded muscle on the lateral surface of the cranial part of
the tail.

_Origin_ from the medial side of the dorsal border of the ilium, and
from the dorsal surface of the sacrum. The muscle passes caudad, lying
just ventrad of the extensor lateralis, and is _inserted_ into the
transverse processes and lateral surfaces of the caudal vertebræ, as far
back as the eighth or ninth.

_Action._--Bends the tail sideways.

=M. abductor caudæ internus= (or M. coccygeus).--A large flat muscle,
having origin on the spine of the ischium. The muscle passes
dorsomediad, spreading out, and is inserted into the transverse
processes of the second to the fourth caudal vertebræ.

_Relations._--Lateral surface with the caudofemoralis (Fig. 68, _s_),
gluteus maximus, and pyriformis. Medial surface with the iliocaudalis
and the flexor caudæ longus (Fig. 68, _x_).

=M. iliocaudalis= (Str.-D.) (Fig. 162, 11′, page 398).--This represents
a portion of the levator ani of man, and in some specimens is united
with that muscle (Fig. 162, 11) in the cat.

_Origin_ along the ventral half of the medial surface of the ilium,
caudad of the sacrum. The fibres pass caudad and are _inserted_ by a
flat tendon into the ventral surface of the caudal vertebræ, from the
second or third to about the seventh.

_Relations._--Lateral surface with the gluteus maximus and abductor
caudæ internus (Fig. 68, _w_). Medial surface with the levator ani (Fig.
162, 11), with which this muscle may be partly united.

_Action._--The two muscles together flex the tail.

=M. flexor caudæ longus= (Fig. 162, 12; Fig. 113, _c_, page 270).

_Origin_ on the ventral surface of the last lumbar vertebra, of the
sacrum, and of the transverse processes of the caudal vertebræ. Caudad
the muscle forms long, strong tendons which are _inserted_ on the
ventral surface of the tail.

_Relations._--Lateral surface with the ilium, the gluteus maximus, the
abductor caudæ internus, the iliocaudalis, and the skin of the tail.
Dorsally it touches in the caudal region the abductor caudæ externus
(Fig. 68, _w_), medially the flexor caudæ brevis (Fig. 162, 13).

_Action._--Flexes the tail.

=M. flexor caudæ brevis= (Fig. 162, 13).

_Origin_ on the ventral surface of the caudal vertebræ, from the first
to the seventh or eighth. The principal head comes from the first
vertebra. The bundles thus formed pass caudad and are inserted each into
the ventral surface of a vertebra some distance caudad of the origin.
The muscle extends to about the tenth caudal vertebra, and its most
caudal parts are closely interconnected with the flexor caudæ longus.

_Relations._--Lateral edge with the flexor caudæ longus. Medial edge in
the sacral region with the levator ani (Fig. 162, 11) and the
iliocaudalis (Fig. 162, 11′); in the caudal region with the muscle of
the opposite side.

_Action._--Flexes the tail.


2. =Muscles on the Ventral Side of the Vertebral Column.=


A. LUMBAR AND THORACIC REGIONS.--The iliopsoas (Fig. 162, 8) belongs in
this group, but since it moves the leg it is described with the muscles
of the pelvic limbs.

=M. psoas minor= (Fig. 162, 9, page 398).--This muscle lies along the
ventral surface of the vertebral column, next to the peritoneum, and
extends from the thoracic vertebræ to the ilium.

_Origin_ usually by five heads, from the caudal border of the centra of
the last two (or one) thoracic and first three (or four) lumbar
vertebræ. These heads also serve as origin for a part of the iliopsoas,
and are closely united at their origin with the quadratus lumborum. They
unite to form an, at first, rather large flat muscle, which rapidly
becomes smaller caudad, finally forming a slender tendon which is
_inserted_ on the iliopectineal line, just craniad of the acetabulum.

_Relations._--Dorsolateral surface with the quadratus lumborum and
iliopsoas (Fig. 162, 8). Ventral surface with the pleura and diaphragm
near the origin; with the peritoneum caudad.

_Action._--Flexes the back in the lumbar region.

=M. quadratus lumborum.=--A flat muscle lying on the ventral surface of
the transverse processes of the lumbar vertebræ. Craniad it has origin
on the ventral surface of the last two thoracic vertebræ, and by a few
fibres from the last rib. The muscle passes caudad, lying on the lateral
side of the psoas minor (Fig. 162, 9), and becomes attached to each of
the transverse processes of the lumbar vertebræ. Caudad the muscle
passes into a strong flat tendon which is inserted into the anterior
inferior spine of the ilium.

_Relations._--Dorsal surface with the transverse processes and the
intertransverse muscles. Ventral and medial surfaces with the psoas
minor (Fig. 162, 9) and iliopsoas (Fig. 162, 8).

_Action._--Bends the vertebral column sideways.


B. MUSCLES ON THE VENTRAL SIDE OF THE NECK (Fig. 65, page 109).--=M.
sternomastoideus= (Fig. 65, _g_; Fig. 68, _c_).--The sternomastoid
(sternal portion of the human sternocleidomastoid) is a flat band one to
three centimeters wide extending from the cranial end of the manubrium
and the midventral line craniad of it to the lambdoidal ridge.

The _origin_ extends from the cranial end of the manubrium along the
midventral line as far as the caudal border of the cricoid cartilage,
and is in two parts. The =caudal= portion arises from the lateral
surface of the manubrium along the dorsal half of its cranial end, and
from the median raphe for about one centimeter craniad of the manubrium.
Its fibres are parallel and tend to diverge into two layers. The
=cranial= portion arises by means of fibres which cover the median line
and interdigitate with the fibres of the opposite muscle between the
cricoid cartilage and a point a few millimeters craniad of the
manubrium. Its caudal border is thus overlaid by the caudal portion. Its
fibres converge and join those of the caudal portion. The muscle passes
dorsocraniad and is

_Inserted_ by means of a flat tendon into the lateral half of the
lambdoidal ridge and into a continuation of the ridge onto the mastoid
portion of the temporal bone as far as the mastoid process. The thickest
part of the tendon is inserted into the mastoid process.

_Relations._--Outer surface at the caudal end with the pectoralis major
(Fig. 65, _l_); in the middle part with the platysma, the depressor
conchæ (Fig. 64, _b_), and with the external jugular vein (Fig. 65, 5),
which crosses it obliquely; at the cranial end with the submaxillary
(Fig. 65, 2) and parotid (1) glands. Inner surface with the sternohyoid
(Fig. 65, _e_), sternothyroid (_g′_), internal jugular vein, longus
capitis muscle, the cleidomastoid (_h_), levator scapulæ ventralis
(_i_), a large lymphatic gland ventrad of the ear, and the splenius
(Fig. 73, _b_).

_Action._--One muscle turns the head and depresses the snout. Both
together depress the snout.

=M. sternohyoideus= (Fig. 65, _e_).--A slender muscle on the midventral
line of the neck close to the opposite muscle.

_Origin_ from the cranial border of the first costal cartilage. The
muscle passes craniad closely united near its caudal end to the
sternothyroid (_g′_).

_Insertion_ (Fig. 67, _m_) into the outer half of the ventral surface of
the body of the hyoid bone caudad of the origin of the geniohyoid (Fig.
67, _g_).

_Relations._--Outer surface with the sternomastoid (Fig. 65, _g_). Inner
surface with the thyrohyoid (Fig. 65, _f_; Fig. 67, _p_), the trachea
(Fig. 67, 4), and the larynx.

_Action._--Draws the hyoid caudad. Raises the ribs and sternum when the
hyoid is fixed.

=M. sternothyreoideus= (Fig. 65, _g′_).--The sternothyroid lies beneath
the sternohyoid and is connected with it at its caudal end.

_Origin_ from the first costal cartilage beneath the sternohyoid.

_Insertion_ (Fig. 67, _o_) into the lateral part of the caudal border of
the thyroid cartilage of the larynx.

_Relations._--Outer surface with the sternohyoid (Fig. 65, _e_) and
laterally with the sternomastoid (Fig. 65, _g_). Inner surface with the
trachea (Fig. 67, 4), and at the lateral edge with the thyroid gland
(Fig. 67, 6).

_Action._--Pulls the larynx caudad.

=M. scalenus= (Fig. 73, _f_-_f‴_).--This is a large and complex muscle
lying on the ventral side of the neck and the lateral surface of the
thorax. It might equally well be classified with the muscles of the
thorax. It is divisible into a considerable number of interconnected
bundles which are sometimes described as separate muscles.

The largest, middle portion (=scalenus medius=) (_f′_) takes origin by
thin tendons from the sixth, seventh, eighth, and ninth ribs, just
dorsad of their junction with the cartilages; these tendons unite near
their origins to form a flat band which becomes fleshy at about the
fifth rib, passes craniad, and unites just craniad of the first rib with
the other parts of the muscle. The dorsal portion (=scalenus posterior=)
(_f″_) has origin by a very slender tendon from about the middle of the
outer surface of the third or fourth rib; it extends craniad as a narrow
band which passes laterad between the heads of the serratus anterior
(_i_) that are attached to the second and third (or third and fourth)
ribs, and unites with the other heads. The ventral head (part of
=scalenus anterior=) (_f‴_) arises by one or two minute tendons from the
cartilages of the second and third ribs; they are partly united with the
transversus costarum (_j_). This ventral head passes craniad and unites
with the other heads.

These three divisions unite just craniad of the first rib with each
other and with the cervical portion of the muscle (_f_) (part of
=scalenus anterior=). This consists of a number of small bundles of
fibres which arise from the first rib and the transverse processes of
the first thoracic and the last six cervical vertebræ.

The _insertion_ is onto the transverse processes of all the cervical
vertebræ, including the axis and atlas. According to Strauss-Durckheim
the fibres from any given transverse process are inserted into the
transverse processes of all the vertebræ craniad of it.

The muscle is partly continuous craniad with the longus capitis (_e_).
The cervical nerves pass out between the bundles of the cervical
portion.

_Relations._--Outer (lateral) surface in the thoracic region with the
external oblique (Fig. 68, _p_), the pectoralis minor (Fig. 65, _o_),
and in part with the serratus anterior (Fig. 73, _i_); in the cervical
region with the sternomastoid (Fig. 65, _g_). Inner (medial) surface
with the serratus anterior (Fig. 73, _i_), the levator scapulæ (Fig. 73,
_h_), the longus atlantis, the transverse processes of the cervical
vertebræ, and the longus capitis (Fig. 73, _e_).

_Action._--Flexes the neck and draws the ribs craniad.

=M. longus capitis= (or =rectus capitis anterior major=) (Fig. 72, _a_;
Fig. 73, _e_).--This is a long muscle lying on the ventral aspect of the
cervical vertebræ. With the muscle of the opposite side and the
underlying longus colli (Fig. 72, _g′_) it forms a trough in which lie
the œsophagus, pharynx, and trachea.

_Origin_ by five (or six) heads from the ventral margins of the
transverse processes of the cervical vertebræ from the second to the
sixth inclusive. The heads unite into a common belly, the lateral border
of which is united with the levator scapulæ ventralis (Fig. 72, _c_)
near its insertion.

_Insertion_ into the body of the sphenoid bone between the bulla and the
middle line. The insertion extends craniad onto the basisphenoid.

_Relations._--Ventral surface with the sternomastoid (Fig. 65, _g_) and
the large lymphatic gland ventrad of the external ear. Lateral surface
with the scalenus (Fig. 72, _h_) and craniad with the levator scapulæ
ventralis (Fig. 72, _c_-_c″_). Medial surface with the carotid artery,
the trachea, œsophagus, and pharynx. Dorsal edge with the vertebræ, the
longus colli (Fig. 72, _g′_), and the rectus capitis anterior minor
(Fig. 72, _b_).

_Action._--Lowers the snout.

=M. rectus capitis anterior minor= (Fig. 72, _b_).--This is a flat band
beneath (dorsad of) the longus capitis (_a_).

_Origin_ from the ventral surface of the inferior arch (body) of the
atlas (3) for about five millimeters laterad of the middle line.

_Insertion_ into a deep depression on the basioccipital caudad of the
insertion of the longus capitis (_a_) and between the caudal end of the
bulla (1) and the median line.

_Relations._--Ventral surface with the longus capitis (_a_). Dorsal
surface with the anterior (ventral) atlanto-occipital membrane (2).

_Action._--Depresses the snout.

  [Illustration: FIG. 72.--MUSCLES ON THE VENTRAL SURFACE OF THE
  CERVICAL VERTEBRÆ.

  On the left side the longus capitis and one head of the levator
  scapulæ ventralis have been cut, in order to show the rectus capitis
  anterior minor. _a_, M. longus capitis; _b_, M. rectus capitis
  anterior minor; _c_, M. levator scapulæ ventralis (_c′_, its atlantal
  head; _c″_, its occipital head); _d_, M. rectus capitis lateralis;
  _e_, M. obliquus capitis superior; _f_, M. longissimus capitis; _g_,
  M. longus colli (_g′_, its cervical portion; _g″_, its thoracic
  portion); _h_, part of M. scalenus. 1, bulla tympani; 2, ventral
  atlanto-occipital membrane; 3, ventral arch of atlas; 4, first rib.]

=M. rectus capitis lateralis= (Fig. 72, _d_).--This lies ventrad of the
obliquus superior (_e_) on the ventral face of the transverse process of
the atlas and at first appears to be a part of the obliquus superior.

_Origin_ from the median half of the ventral surface of the transverse
process of the atlas. The fibres form a cylindrical mass which passes
craniad and slightly laterad.

_Insertion_ into the fossa laterad of the condyle of the occipital bone.

_Relations._--Ventral surface with the digastric (Fig. 65, _b_) and the
lymphatic gland ventrad of the ear. Dorsal surface with the wing of the
atlas.

_Action._--Flexes the head laterally.

=M. longus colli= (Fig. 65, _g′_, _g″_).--A long, rather slender muscle
lying on the ventral surface of the cervical and first six thoracic
vertebræ. It consists of many separate bundles, and is divisible into a
thoracic and a cervical portion.

The =thoracic portion= (_g″_) has origin by six heads from the ventral
surface of the first six thoracic vertebræ. The separate heads join to
form a band which passes craniad and is inserted for the most part into
the processus costarius of the sixth cervical vertebra; a portion of it
joins the cervical division of the muscle.

The =cervical portion= (_g′_) is a continuation craniad of the thoracic
portion. It arises in small bundles from the transverse processes and
sides of the ventral surfaces of the centra of the cervical vertebræ.
These bundles pass craniomediad, so that those from the muscles of
opposite sides meet and are inserted on the centra of the vertebræ in
the middle line, each pair of bundles forming a V opening caudad. The
most cranial insertion is into the tubercle on the middle of the ventral
surface of the ventral arch of the atlas (3).

_Relations._--Dorsal surface with the centra of the vertebræ. Ventral
surface in the thorax with the trachea; in the neck with the œsophagus.
Medial edge with the muscle of the opposite side. Lateral margin in the
cervical region with the longus capitis (_a_).

_Action._--Bends the neck.


3. =Muscles of the Thorax.=


A. BREAST-MUSCLES (connecting the arm and thorax) (Fig. 65, page 109).

The muscles connecting the arm with the sternum, corresponding to the
pectoralis muscles of man, fall into a considerable number of not always
clearly separated bundles in the cat. We shall distinguish by name four
such bundles; these might be, and frequently are, further subdivided.

=M. pectoantibrachialis= (Fig. 65, _m_).--This is a small flat bundle
about one or two centimeters wide, forming the most superficial portion
of the pectoralis group.

_Origin_ on the lateral surface of the manubrium. The muscle passes
laterad onto the arm and is _inserted_ by a flat tendon into the
superficial fascia of the dorsal border of the forearm, near the
elbow-joint. The tendon is continuous craniad with the border of the
clavobrachial (_k_), so that a bundle of fibres may pass from this
muscle to be inserted with the clavobrachial, or a bundle from the
clavobrachial to be inserted with this. The tendon is continuous caudad
with that of the epitrochlearis (_r_). The fascia of insertion may be
traced to an attachment into the dorsal border of the ulna. This muscle
usually receives near its insertion a slip, sometimes called its caudal
division, from the deep layer of the pectoralis major.

_Relations._--Outer surface with the integument. Inner surface with both
divisions of the pectoralis major (_l_) on its medial two-thirds, and
with the biceps (_t_) and bicipital arch (_t′_) in its lateral
one-third. The cranial border is closely applied to that of the
clavobrachial (_k_), except at the two ends.

_Action._--Draws the arm mediad.

=M. pectoralis major=, or =ectopectoralis= (Fig. 65, _l_, _l′_).--In
this it is usually possible to distinguish a superficial and a deep
layer.

The =superficial= (_l′_) layer is a flat band of fibres one or two
centimeters wide.

_Origin_ from a raphe in the midventral line, along the cranial half of
the manubrium and for five to ten millimeters craniad of it.

_Insertion_ (Fig. 81, _f_).--The pectoral ridge of the middle third of
the shaft of the humerus, slightly dorsad of the line of insertion of
the deep portion.

_Relations._--Outer surface with the clavobrachial (Fig. 65, _k_) and
integument, the medial end caudally with the pectoantibrachialis (_m_),
and the distal end with the brachialis (_v_). Inner surface with the
deep portion (_l_), the fibres of which it crosses obliquely.

The =deep portion= (_l_) is a flat band of parallel fibres about three
times as broad as the superficial portion.

_Origin._--The ventral surface of the manubrium and of the first three
divisions of the sternum, and the median raphe for about one centimeter
craniad of the manubrium. It passes directly laterad.

_Insertion_ (Fig. 81, _e_) along a line which begins at the
infraspinatus fossa of the great tuberosity, and runs parallel to the
deltoid ridge until it reaches the pectoral ridge at the junction of the
second and third fourths of the humerus and then continues in the
direction of the pectoral ridge as far as the junction of the third and
fourth fourths of the humerus. Some of its fibres may pass caudad of the
biceps and be inserted with the epitrochlearis. Into the part of the
line which is parallel to the deltoid ridge the muscle is inserted by a
flat tendon; into the remainder of the line it is usually inserted
directly by muscle-fibres, though at its caudal end its insertion may
again be tendinous.

_Relations._--Outer surface with the cutaneus maximus, the outer layer
of the pectoralis major (Fig. 65, _l′_), the pectoantibrachialis (_m_),
and the clavobrachial (_k_). Inner surface with the pectoralis minor
(_o_), the proximal end of the humerus, the coracobrachialis (Fig. 77,
_f_), and the supraspinatus (Fig. 77, _d_) at the insertion of the
latter. At the cranial part of its origin it touches the sternomastoid
(Fig. 65, _g_) and sternohyoid (Fig. 65, _e_).

_Action._--Draws the arm mediad and turns the foot forward.

=M. pectoralis minor=, or =entopectoralis= (Fig. 65, _o_).--This is a
fan-shaped mass of fibres, flat but thicker than the pectoralis major.

_Origin_ from the lateral half of the first six divisions of the body of
the sternum and sometimes from the xiphoid process. The fibres are
divisible into several bundles which vary in extent and distinctness and
are sometimes described as separate muscles. They pass craniolaterad and
converge so that the line of insertion is about one-half as long as that
of the origin.

_Insertion_ (Fig. 81, _d_) into the humerus along a line which forms the
ventral border of the bicipital groove at the proximal end of the bone,
passes thence onto the pectoral ridge and continues in the direction of
the pectoral ridge nearly as far as the middle of the length of the
humerus. The cranial and caudal fibres are inserted by means of a thin
tendon; the middle fibres directly. The cranial border of the tendon of
insertion is continued as a thin tendon to the coracoid process; it is
closely united with the insertion of the supraspinatus.

_Relations._--By its outer surface with the pectoralis major (Fig. 65,
_l_) over its cranial half; with the cutaneus maximus, latissimus dorsi
(Fig. 65, _q_), and integument over its caudal half. By its inner
surface with the xiphihumeralis (Fig. 65, _p_), rectus abdominis (Fig.
73, _k_), and a mass of fat in the axilla. The tendon of the
xiphihumeralis is also connected with its inner surface near its
insertion. Its cranial border is free. Its caudal border is in relation
at its medial end with the xiphihumeralis, at its lateral end with the
tendon of the latissimus dorsi (Fig. 65, _q_).

_Action._--Draws the arm toward the middle line.

=M. xiphihumeralis= (Fig. 65, _q_).--A long, thin, narrow muscle which
may be considered as part of the pectoralis minor.

_Origin_ a median raphe along the xiphoid process or at an angle to the
median line on the rectus abdominis muscle. It passes craniad, becoming
gradually smaller, and about two centimeters from its insertion ends in
a thin tendon.

_Insertion._--It ends in a flat tendon which in passing is connected by
a strong fascia with the tendon of the latissimus (Fig. 65, _q_). It
passes along the inner surface of the pectoralis minor (_o_) to be
inserted with its cranial fibres near the ventral border of the
bicipital groove.

_Relations._--Outer surface with the cutaneus maximus at its medial end,
with the pectoralis minor (_o_) at its distal end. Inner surface with
the external oblique (Fig. 68, _p_), the rectus abdominis (Fig. 73,
_k_), and a mass of fat in the axilla. Borders free. Some of the fibres
of the cutaneus maximus are attached to its outer surface.

_Action._--Assists the pectoralis minor.


B. MUSCLES OF THE WALL OF THE THORAX.

=M. serratus posterior superior= (Fig. 73, _l_).--A thin sheet of muscle
and tendon beneath the serratus anterior (_i_) on the dorsal part of the
thorax and neck.

_Origin_ by fleshy slips from the outer surfaces of the first nine ribs
just ventrad of their angles. The origin may extend as far as the tenth
or eleventh ribs. The first slip is usually delicate. The fibres are
directed dorsad and craniad and unite to form a continuous sheet. This
ends along a longitudinal line opposite the vertebral transverse
processes in the aponeurosis which covers the longissimus dorsi and
other muscles in this region. Its insertion is into the median dorsal
raphe between the axial spinous process and the tenth thoracic spinous
process.

_Relations._--Outer surface with the serratus anterior (_i_), the
latissimus dorsi (Fig. 68, _m_), and the rhomboideus. Inner surface with
the external intercostals (Fig. 73, _m_), the iliocostal (Fig. 69, _h_),
the longissimus dorsi (Fig. 69, _f_), the spinalis dorsi (Fig. 69, _g_),
and the splenius (Fig. 73, _b_).

_Action._--Draws the ribs craniad.

=M. serratus posterior inferior= (Fig. 73, _n_).--The serratus posterior
inferior is a thin muscle lying caudad of the serratus posterior
superior (_l_) and sometimes overlying the caudal end of the latter.

_Origin_ by four or five heads from the last four or five ribs. In some
specimens only three heads may be present. The separate bundles pass
dorsocaudad and unite to form a continuous sheet which ends in a
continuation of the aponeurosis of the serratus posterior superior
(_l_).

_Insertion_ into the lumbar spinous processes and the intervening
interspinous ligaments.

_Relations._--Outer surface with the latissimus dorsi (Fig. 68, _p_),
and at the origins with the intercostales externi (Fig. 73, _m_). Inner
surface with the intercostales interni (Fig. 69, _k_) at the origin and
with the intercostales externi (Fig. 69, _i_), iliocostal (Fig. 69,
_h_), longissimus dorsi (Fig. 69, _f_), and the caudal end of the
spinalis dorsi (Fig. 69, _g_).

  [Illustration: FIG. 73.--BODY MUSCLES EXPOSED AFTER REMOVAL OF THE
  FORELIMB AND THE MUSCLES SHOWN IN FIG. 68.

  _a_, M. occipitoscapularis (cut); _b_, M. splenius; _c_, M. levator
  scapulæ ventralis (cut); _d_, M. cleidomastoideus (cut); _e_, M.
  longus capitis; _f_, M. scalenus (_f′_, middle division; _f″_, dorsal
  division; _f‴_, ventral division; _f_, cervical portion); _g_, M.
  longissimus capitis; _h_, M. levator scapulæ (cut); _i_, M. serratus
  anterior (cut); _j_, M. transversus costarum; _k_, M. rectus abdominis
  (_k′_, its tendon); _l_, M. serratus posterior superior; _m_, M.
  intercostales externi; _n_, M. serratus posterior inferior; _o_, M.
  obliquus abdominis internus; _p_, lumbodorsal fascia.]

_Action._--Assists the serratus posterior superior.

=M. transversus costarum=, or =sternocostalis externus= (Fig. 73,
_j_).--This is a thin muscle applied to the cranial part of the side of
the thorax, covering the cranial end of the rectus abdominis (_k_).

_Origin_ by tendon from the side of the sternum between the attachments
of the third and sixth ribs. The muscle passes dorsocraniad to its

_Insertion_ on the first rib and the lateral portion of its costal
cartilage.

_Relations._--Outer surface with the pectoralis minor (Fig. 65, _o_).
Inner surface with the scalenus (Fig. 73, _f‴_), the rectus abdominis
(Fig. 73, _k_), and the intercostales externi (Fig. 73, _m_). At its
insertion it is united with a portion of the scalenus (Fig. 73, _f‴_).

_Action._--Draws the sternum forward.

=Mm. levatores costarum.=--Small muscles having _origin_ on the
transverse processes of the thoracic vertebræ, passing caudoventrad, and
becoming _inserted_ on the angle of the rib lying immediately caudad of
the origin. They are continuous with the external intercostals.

_Relations._--Outer surface with the longissimus dorsi (Fig. 69, _f_),
and craniad with the iliocostal (Fig. 69, _h_). Inner surface with the
internal intercostals (Fig. 69, _k_).

_Action._--Pull the ribs dorsocraniad.

=Mm. intercostales externi= (Fig. 73, _m_; Fig. 69, _i_).--The external
intercostals are placed in the outer portion of the intercostal spaces.
They are composed of bundles of fibres attached by their ends to the
adjacent borders of the ribs and having in general the direction of the
external oblique muscle, i.e., they pass from their cranial ends
caudoventrad. They occupy the intercostal spaces between the true ribs
and extend even caudad into the spaces between the false ribs. They are
lacking between the ventral ends of the costal cartilages of the first
six to eight ribs, so that the internal intercostals (Fig. 69, _k_) are
here exposed. The more caudal external intercostals are more nearly
craniocaudal in direction.

_Relations._--Outer surface with obliquus abdominis externus (Fig. 68,
_p_), latissimus dorsi (Fig. 68, _m_), serratus posterior inferior (Fig.
73, _n_) and superior (Fig. 73, _l_), serratus anterior (Fig. 73, _i_),
scalenus (Fig. 73, _f_), and iliocostal (Fig. 69, _h_). Inner surface
with the internal intercostals (Fig. 69, _k_).

_Action._--Protractors of the ribs.

=Mm. intercostales interni= (Fig. 69, _k_).--The internal intercostals
are similar to the external intercostals, beneath which they lie. Their
fibres pass between the ribs at nearly right angles to those of the
external intercostals and have nearly the direction of the fibres of the
internal oblique. They occupy all the intercostal spaces from the first
to the thirteenth ribs.

_Relations._--Outer surface with the external intercostals (Fig. 69,
_i_), and ventrad with the scalenus (Fig. 73, _f_), transversus costarum
(Fig. 73, _j_), and rectus abdominis (Fig. 73, _k_). Inner surface with
the pleura and the transversus thoracis.

_Action._--Retractors of the ribs.

=M. transversus thoracis= (triangularis sterni; sternocostalis
internus).--This represents a thoracic portion of the transversus
abdominis. It consists of five or six flat muscular bands lying on the
inner surface of the thoracic wall.

_Origin_ on the lateral borders of the dorsal face of the sternum,
opposite the attachments of the cartilages of the third to the eighth
ribs. The six bands thus formed, each about one centimeter wide, pass
laterad and are _inserted_ into the cartilages of the ribs near their
junction with the ribs, and into the fascia which covers the inner
surface of the internal intercostals in this region.

_Relations._--Outer surface with the internal intercostals and the
cartilages of the ribs. Inner surface with the pleura.

=Diaphragma= (Fig. 74).--The diaphragm consists of a central so-called
=semilunar= tendon (_e_) and of muscular fibres which pass radially from
the body wall to the tendon. It forms a complete oblique partition
between the abdominal and thoracic cavities. The dorsal end is farther
caudad than the ventral.

The central tendon (_e_) is thin and irregularly crescent-shaped, with
the convexity ventrad and the horns of the crescent prolonged as two
tendinous bands (_e′_) which end in two triangular =membranous= portions
(_d_) of the diaphragm, one on each side of the spinal column. It is
pierced by an opening for the vena cava (_f_).

  [Illustration: FIG. 74.--DIAPHRAGM, CAUDAL SURFACE SEEN OBLIQUELY FROM
  THE RIGHT.

  _a_, right crus; _b_, left crus; _c_, _c′_, sternocostal part of
  diaphragm; _d_, _d′_, membranous portions of the diaphragm; _e_,
  central tendon; _e′_, prolongations of central tendon; _f_, opening
  for posterior vena cava; _g_, œsophagus; _h_, aorta; _i_, M.
  transversus abdominis.]

The muscular portion is in two parts: (_a_) The =vertebral= portion (_a,
b_) arises by a single tendon from the ventral surface of the second,
third, and fourth lumbar centra. The tendon diverges into two, the right
one (_a_) of which is much stronger, and from each of the two arise
muscle-fibres. Each mass of fibres is one of the two =crura= (sing.
=crus=) of the diaphragm. The aorta (_h_) enters the abdomen between the
crura dorsally. The fibres of each crus diverge to be inserted into the
central tendon and the dorsal continuation of its horn. The two sets of
fibres unite ventrad of the opening of the aorta. Between this opening
and the central tendon is another opening for the œsophagus (_g_); this
lies entirely in that part of the diaphragm which arises from the right
crus (_a_). The fibres are again united ventrad of the œsophageal
opening.

(_b_) The =sternocostal part= (_c_, _c′_) takes origin from the
xiphoid process and the last five ribs, by fleshy bundles which
interdigitate with those of the transversus abdominis (_i_). The fibres
converge to the central tendon (_e_). Between the crus of each side and
the most dorsal of the costal fibres is the membranous interval (_d_)
mentioned above.


4. =Abdominal Muscles.= =M. obliquus abdominis externus= (Fig. 68,
_p_).--A large, thin sheet of muscle covering the whole abdomen and part
of the thorax ventrally.

_Origin._--(_a_) From the last nine or ten ribs by means of as many
tendons, which are interconnected to form arches that span the slips of
the serratus anterior. The muscle-fibres arise from these tendons and
from their intervening arches. (_b_) From the lumbodorsal aponeurosis
common to it and the internal oblique. The cranial fibres pass nearly
ventrad, the caudal fibres caudad, and the intervening fibres take an
intermediate course. The fibres end in a thin aponeurosis of insertion
along a curved line which passes at first caudad and then laterodorsad.
The aponeurosis fibres continue in the direction of the muscle-fibres to
the

_Insertion_ into the median raphe ventrad of the sternum from the
insertion of the seventh costal cartilage to the xiphoid process, into
the linea alba from the sternum to the pubic tubercle, and into the
tubercle and the cranial border of the pubis. Caudad of the xiphoid
process the aponeurosis is closely united to the superficial layer of
the internal oblique, where it forms the outer layer of the sheath of
the rectus abdominis. Laterad of the pubic tubercle the tendon is
perforated by the inguinal canal. In the cat neither the caudal part of
the muscle nor its tendon is attached to the ilium, as it is in man and
the dog, so that no Poupart’s ligament, or inguinal ligament, is formed.

_Relations._--Outer surface with the cutaneus maximus, the integument,
and near the origin with the latissimus dorsi (Fig. 68, _m_). Inner
surface with the obliquus internus (Fig. 73, _o_), the rectus abdominis
(Fig. 73, _k_), the intercostales externi (Fig. 73, _m_), a small part
of the serratus posterior inferior (Fig. 73, _n_), and by its dorsal
tendon with the longissimus dorsi (Fig. 69, _f_).

_Action._--Constrictor of the abdomen.

=M. obliquus abdominis internus= (Fig. 73, _o_).--A thin sheet similar
to the preceding but of less extent. Its fibres cross those of the
external oblique nearly at right angles and lie beneath them.

_Origin._--(1) Between the fourth and seventh lumbar vertebræ from the
lumbar aponeurosis which is common to it and the external oblique. The
lumbar aponeurosis takes origin from the lumbar spinous processes and
the interspinous ligaments, and is continuous craniad with the
aponeurosis of the serratus posterior inferior. Laterad it splits into
three sheets, two for the above-named muscles and a third which passes
to the vertebral transverse processes and forms the fascia covering the
supraspinous muscles of the lumbar region. (2) By a similar aponeurosis
from the ventral half of the iliac crest. (3) By fleshy fibres from the
three =crural arches=. These are three delicate ligamentous arches which
stretch from the crest of the ilium to the pubic spine. The dorsal one
gives exit to the iliopsoas muscle, the middle to the femoral vessels,
and the ventral to the spermatic cord. In the female the middle and
ventral arches may fuse. The pillar between the dorsal and middle arches
is attached to the iliopectineal eminence.

_Insertion._--The fibres pass cranioventrad and end along a longitudinal
line in a thin aponeurosis of insertion, which is united in the linea
alba to those of the external oblique and transversus. At the caudal end
of the aponeurosis all its fibres pass outside of the rectus abdominis
(Fig. 73, _k_). At its cranial end the fibres divide into two sheets or
laminæ, one of which passes outside of the rectus and the other inside.
The outer lamina unites with the aponeurosis of the external oblique,
while the inner lamina unites with that of the transversus. There is
thus formed a sheath for the cranial part of the rectus muscle.

_Relations._--Outer surface with the obliquus externus (Fig. 68, _p_).
Inner surface with the transversus abdominis (Fig. 69, _l_), and by its
ventral tendon with the rectus.

_Action._--Compressor of the abdomen.

=M. transversus abdominis= (Fig. 69, _l_).--A thin sheet covering the
whole surface of the abdomen and lying beneath the internal oblique. Its
fibres are nearly transverse.

_Origin._--(1) By fleshy fibres or by a thin aponeurosis from the
cartilages of all the false and floating ribs, by interdigitation with
the fibres of the diaphragm. (2) From the tips of all the lumbar
transverse processes. (3) From the ventral border of the ilium. (4) From
the dorsal and middle of the three crural arches, where it may blend
partly with the internal oblique. The muscle is continuous craniad with
the transversus thoracis muscle. Near the lateral border of the rectus
abdominis the muscle ends in a thin aponeurosis of insertion which is
continued (its fibres having the direction of the muscle-fibres) to the

_Insertion_ in the linea alba.

_Relations._--Outer surface with the internal oblique (Fig. 73, _o_) and
the rectus abdominis (Fig. 73, _k_), dorsad also with the longissimus
dorsi (Fig. 69, _f_). Inner surface with a thin fascia covering the
peritoneum and ventrocaudad with the rectus (Fig. 73, _k_). The dorsal
edge of the muscle touches the iliopsoas and longissimus dorsi; the
ventral edge touches the muscle of the opposite side.

_Action._--Constrictor of the abdomen.

=M. rectus abdominis= (Fig. 73, _k_).--A rather thick, flat muscle which
lies near the median ventral line separated by the linea alba from its
fellow of the opposite side and stretching from the pubis to the first
costal cartilage. Opposite the first lumbar vertebra it is approximately
four centimeters wide. It narrows at both ends.

_Origin_ by a strong tendon from the tubercle of the pubis. The muscle
passes craniad at first between the peritoneal fascia and the
transversus aponeurosis, then in the sheath formed by the internal and
external oblique and the transversus aponeurosis. It emerges from the
sheath opposite the xiphoid process and passes ventrad of the costal
cartilages. Between the third and fourth costal cartilages it ends in a
thin tendon which passes beneath the transversus costarum and is

_Inserted_ into the first costal cartilage near its middle, into the
second costal cartilage near its sternal end, and into the sternum
between the first and fourth cartilages.

_Relations._--Outer surface of the cranial part of the muscle and its
tendon with the pectoralis minor (Fig. 68, _o_) and the transversus
costarum (Fig. 73, _j_); caudad the muscle is covered by the outer layer
of the rectus sheath. Lateral edge with the obliquus externus (Fig. 68,
_p_), obliquus internus (Fig. 73, _o_), and transversus abdominis (Fig.
69, _l_). Medial edge with the muscle of the opposite side. Inner
surface with the internal intercostals (Fig. 69, _k_) and the rib
cartilages; the inner layer of the rectus sheath and the peritoneum.

_Action._--Retracts the ribs and sternum and compresses the abdomen.


IV. MUSCLES OF THE THORACIC LIMBS.

The muscles connecting the thoracic limbs with the rest of the body have
been described.


1. Muscles of the Shoulder.


A. MUSCLES ON THE LATERAL SURFACE OF THE SHOULDER.

=M. deltoideus.=--The deltoid muscle of the cat is divided into two (or
three) portions which are together equivalent to the human deltoid.
These are the spinodeltoid, the acromiodeltoid, and possibly the
clavobrachial, which is frequently called clavodeltoid.

=M. spinodeltoideus= (Fig. 75, _e_; Fig. 68, _i_).--A rather thick, flat
muscle between the scapular spine and the deltoid ridge of the humerus.
It forms a chord of the angle between the glenoid border of the scapula
and the humerus.

_Origin_ by short tendon-fibres from the glenoid border of somewhat more
than the middle third of the spine of the scapula (Fig. 76, _g_), and
from a tendinous raphe between the spinotrapezius (Fig. 68, _j_),
acromiotrapezius (Fig. 68, _h_), and infraspinatus (Fig. 75, _c_). The
origin may pass toward the vertebral border of the scapula onto the
infraspinatus muscle (Fig. 75, _c_).

_Insertion_ (Fig. 81, _h_) by a flat tendon upon the deltoid ridge of
the humerus, nearly parallel to that of the pectoralis major.

_Relations._--Outer surface with the integument and at the insertion
with the acromiodeltoideus (Fig. 75, _f_). Inner surface with the
infraspinatus (_c_), teres minor (Fig. 80, _c_), caput laterale (Fig.
75, _h_), and caput longum (Fig. 75, _g_) of the triceps muscle.

_Action._--Flexes the humerus and rotates it outward.

=M. acromiodeltoideus= (Fig. 75, _f_; Fig. 68, _g_).--A flat muscle
which overlies the distal end of the spinodeltoideus (Fig. 75, _c_). It
connects the acromion with the humerus.

_Origin_ (Fig. 76, _d_).--From the glenoid border of the acromion, and
sometimes the adjacent metacromion as far as the tip.

_Insertion._--Mostly upon the outer surface of the spinodeltoideus (Fig.
75, _c_). The outer fibres are continued to the bone, especially at the
lateral border of the muscle, and are inserted along a line ventrad of
the line of insertion of the spinodeltoideus, and extending farther
distally (Fig. 81, _g_). Some of the outer fibres pass into the
brachialis (Fig. 80, _h_).

_Relations._--Outer surface with the integument and the clavobrachial
(Fig. 68, _e_). Inner surface with the infraspinatus (Fig. 75, _c_),
teres minor (Fig. 80, _c_), spinodeltoid (Fig. 75, _e_), and caput
laterale of the triceps (Fig. 75, _h_).

_Action._--Like that of the spinodeltoid.

=M. clavobrachialis= (Fig. 65, _k_; Fig. 68, _e_).--A flat, triangular
muscle on the cranial surface of the shoulder, forming a direct
continuation of the clavotrapezius (Fig. 68, _d_). These two are
frequently described as constituting a single muscle, the cephalohumeral
or cephalobrachial. (The clavobrachial is frequently given the name
clavodeltoid; as its homology with the human clavodeltoid appears
doubtful, it seems well to use the name clavobrachial, as proposed by
Clasen.)

  [Illustration: FIG. 75.--MUSCLES ON THE LATERAL SURFACE OF THE ARM.

  _a_, M. supraspinatus; _b_, part of insertion of M. rhomboideus; _c_,
  M. infraspinatus; _d_, M. teres major; _e_, M. spinodeltoideus; _f_,
  M. acromiodeltoideus; _g_, caput longum of M. triceps brachii; _h_,
  caput laterale of M. triceps brachii; _i_, M. brachialis; _j_, M.
  biceps; _k_, M. brachioradialis; _l_, M. extensor carpi radialis
  longus; _m_, M. extensor communis digitorum (_m′_, tendon of same);
  _n_, M. extensor lateralis digitorum; (_n′_, tendon of same); _o_, M.
  extensor carpi ulnaris (_o′_, tendon of same); _p_, M. extensor
  indicis proprius; _q_, fifth head of M. flexor profundus digitorum;
  _r_, M. flexor carpi ulnaris. 1, vertebral border of the scapula; 2,
  spine of the scapula; 3, greater tuberosity of the humerus; 4,
  olecranon; 5, transverse ligament of the wrist.]

_Origin._--Its superficial fibres are continuations of the
clavotrapezius (Fig. 68, _d_); other fibres have origin from the
clavicle and from a raphe laterad of the clavicle which is common to
this muscle and the clavotrapezius. It passes distad along the cranial
surface of the arm, growing narrower as it approaches the convexity of
the elbow.

_Insertion._--Eight to ten millimeters from the ulna it joins the
brachialis muscle (Fig. 79, _i_) to be inserted with it by a flat tendon
(Fig. 79, _i_; Fig. 87, _c_) upon a rough area on the medial surface of
the ulna just distad of the semilunar notch, and about midway between
the dorsal and ventral borders.

_Relations._--Outer surface with the integument. Inner surface with the
pectoralis major (Fig. 65, _l_), biceps (Fig. 77, _g_), lateral head of
the triceps (Fig. 75, _h_), acromiodeltoid (Fig. 75, _f_), and
brachialis (Fig. 80, _h_). Medial border with the pectoantibrachialis
(Fig. 65, _m_). Lateral border free except near the insertion, where it
is in relation with the brachialis.

_Action._--Flexor of the antibrachium.

=M. supraspinatus= (Fig. 75, _a_) occupies the whole of the
supraspinatus fossa of the scapula. It is covered by strong fascia which
stretches from the free edge of the spine to the coracoid border of the
scapula and to the coracoid half of its vertebral border.

_Origin_ (Fig. 76, _b_) by fleshy fibres from the whole surface of the
supraspinatus fossa, from the above-mentioned fascia, and from the
subscapularis (Fig. 77, _a_) craniad of the coracoid border of the
scapula.

_Insertion_ (Fig. 83, _a_).--It passes over the capsule of the
shoulder-joint, to which it is closely attached, and is inserted into
the free border of the great tuberosity ventrad (or proximad) of the
fossa for the infraspinatus (Fig. 83, _c_).

_Relations._--Outer surface with the spinotrapezius (Fig. 68, _j_),
acromiotrapezius (Fig. 68, _h_), levator scapulæ ventralis (Fig. 68,
_f_), clavotrapezius (Fig. 68, _d_), and cleidomastoid (Fig. 65, _h_).
Inner surface with the scapula. The distal end of the coracoid border is
closely related to the pectoralis minor (Fig. 79, _f_). The glenoid
border is related to the origin of the deltoidei.

_Action._--Extends the humerus after it has been flexed on the scapula.

=M. infraspinatus= (Fig. 75, _c_).--This fills the infraspinatus fossa,
its fibres converging to the insertion on the great tuberosity of the
humerus.

  [Illustration: FIG. 76.--LATERAL SURFACE OF THE SCAPULA, WITH THE
  AREAS OF ATTACHMENT OF MUSCLES.

  _a_, M. infraspinatus; _b_, M. supraspinatus; _c_, origin of M.
  biceps; _d_, M. acromiodeltoideus; _e_, M. teres minor; _f_, M.
  levator scapulæ ventralis; _g_, M. spinodeltoideus; _h_, M.
  acromiotrapezius; _i_, M. rhomboideus; _j_, M. teres major; _k_-_l_,
  line of insertion of M. spinotrapezius.]

_Origin_ (Fig. 76, _a_).--By fleshy fibres from the whole infraspinatus
fossa, and by a raphe between it and the teres major (Fig. 75, _d_), and
sometimes by fibres from the teres minor (Fig. 80, _c_), triceps,
spinodeltoideus (Fig. 75, _e_), spinotrapezius (Fig. 68, _j_), and
subscapularis (Fig. 77, _a_).

_Insertion_ (Fig. 83, _c_).--By a flat tendon which passes over the
capsule of the joint, into the ventral half of the infraspinatus fossa
on the great tuberosity of the humerus. (The dorsal half of the fossa is
covered by a synovial bursa.)

_Relations._--Outer surface with the spinotrapezius (Fig. 68, _j_),
spinodeltoid (Fig. 68, _i_), acromiodeltoid (Fig. 68, _g_), teres major
(Fig. 75, _d_), and levator scapulæ ventralis (Fig. 68, _f_). Inner
surface with the scapula. Glenoid border with the teres minor (Fig. 80,
_c_), the teres major (Fig. 75, _d_), and the long head of the triceps
(Fig. 75, _g_).

_Action._--Rotates the humerus outward.

=M. teres minor= (Fig. 80, _c_).--A small muscle from the glenoid border
of the scapula to the proximal end of the humerus.

_Origin_ (Fig. 76, _e_) by a sheet of tendinous fibres from the glenoid
border of the scapula beginning about one-fifth the length of the border
from the glenoid fossa and extending to its middle. It is often attached
to the infraspinatus (Fig. 80, _b_) and the caput longum of the triceps
(Fig. 75, _g_).

_Insertion_ (Fig. 83, _d_) by a short tendon into the tubercle just
distad of the infraspinatus fossa on the great tuberosity of the
humerus.

_Relations._--Outer surface with the spinodeltoideus (Fig. 75, _e_),
acromiodeltoideus (Fig. 75, _f_), and the infraspinatus (Fig. 80, _b_).
Inner surface with the lateral (Fig. 75, _h_) and long (Fig. 75, _g_)
heads of the triceps and the capsule of the joint.

_Action._--Assists the infraspinatus to rotate the humerus outward.


B. MUSCLES ON THE MEDIAL SURFACE OF THE SHOULDER.

(Fig. 77.)

=M. subscapularis= (Fig. 77, _a_).--A triangular mass from the
subscapular fossa to the lesser tuberosity of the humerus.

_Origin_ (Fig. 78, _a_).--From the whole subscapular fossa except along
the fusiform area for the attachment of the levator scapulæ and the
serratus anterior near the vertebral border, and except over a
quadrangular area about one centimeter long near the glenoid angle. The
origin is by fleshy fibres directly from the periosteum except along two
or three lines marked by oblique ridges. To these lines are attached
tendinous fibres. At the glenoid border the area of origin sometimes
occupies part or the whole of the surface of the fossa for the origin of
the teres major, so that the teres arises from the fascia on the surface
of the subscapularis. At the coracoid border some of the fibres may take
origin from the adjacent fascia of the supraspinatus (Fig. 77, _d_).

_Insertion_ (Fig. 82, _b_).--The fibres converge to the glenoid border,
and the insertion is by a strong, flat tendon into the dorsal border of
the lesser tuberosity of the humerus.

  [Illustration: FIG. 77.--MUSCLES ON THE MEDIAL SIDE OF THE ARM.

  M. epitrochlearis, M. clavobrachialis, and the breast-muscles have
  been removed. _a_, M. subscapularis; _b_, insertion of M. levator
  scapulæ and of M. serratus anterior; _c_, M. teres major; _d_, M.
  supraspinatus; _e_, M. latissimus dorsi (_e′_, cut edge of that part
  which becomes united with the bicipital arch); _f_, M.
  coracobrachialis; _g_, M. biceps brachii (the capsule of the joint has
  been laid open to show its tendon); _h_, cut insertions of pectoralis
  muscles; _i_, caput longum of M. triceps brachii; _j_, long portion of
  caput mediale of M. triceps brachii; _k_, intermediate portion of
  caput mediale of M. triceps brachii; _l_, short portion of caput
  mediale of M. triceps brachii; _m_, cut end of M. clavobrachialis;
  _n_, M. brachioradialis; _o_, M. extensor carpi radialis longus; _p_,
  M. extensor carpi radialis brevis; _q_, M. pronator teres; _r_, M.
  flexor carpi radialis; _s_, M. palmaris longus (_s′_, its tendons);
  _t_, M. flexor carpi ulnaris (_t_, ulnar head; _t′_, humeral head);
  _u_, third head of M. flexor profundus digitorum; _u′_, fifth head of
  M. flexor profundus digitorum; _u″_, one of the tendons of M. flexor
  profundus digitorum; _v_, M. pronator quadratus; _w_, M. abductor
  brevis pollicis; _x_, ulnar part of M. flexor sublimis digitorum. 1,
  transverse ligament of the wrist.]

_Relations._--Lateral surface with the scapula and the capsule of the
shoulder-joint. Medial surface with the levator scapulæ (Fig. 73, _h_),
serratus anterior (Fig. 73, _i_), part of the scalenus (Fig. 73, _f_),
the transversus costarum (Fig. 73, _j_), and the coracobrachialis (Fig.
77, _f_). Cranial border with the supraspinatus (Fig. 77, _d_). Caudal
border with the teres major (Fig. 77, _c_) and infraspinatus (Fig. 75,
_c_).

_Action._--Pulls the humerus inward (mediad).

=M. teres major= (Fig. 75, _d_; Fig. 77, _c_).--A thick muscle,
triangular in cross-section, lying parallel with the glenoid border of
the scapula.

_Origin_ (Fig. 76, _j_; Fig. 78, _b_) from the vertebral one-third of
the glenoid border of the scapula, and from fascia covering the
subscapularis (Fig. 77, _a_) and the infraspinatus (Fig. 75, _c_) over a
small area near the glenovertebral angle of the scapula. It may touch
the insertion of the rhomboideus.

_Insertion_ (Fig. 82, _f_) by a tendon common to it and the latissimus
dorsi (Fig. 79, _d′_), as already described.

_Relations._--Outer surface with the caput longum (Fig. 75, _g_) and the
long portion (Fig. 80, _f_) of the caput mediale of the triceps, the
latissimus dorsi (Fig. 77, _e_), and the cutaneus maximus. Inner surface
with the serratus anterior (Fig. 73, _i_), the scalenus (Fig. 73, _f_),
the transversus costarum (Fig. 73, _j_), and the biceps (Fig. 77, _g_).
Dorsal border with the subscapularis (Fig. 77, _a_) and infraspinatus
(Fig. 75, _c_).

_Action._--Rotates the humerus inward and flexes it in opposition to the
infraspinatus, teres minor, and the deltoidei.

  [Illustration: FIG. 78.--MEDIAL SURFACE OF THE SCAPULA WITH THE AREAS
  OF ATTACHMENT OF MUSCLES.

  _a_, M. subscapularis; _b_, M. teres major; _c_, M. serratus anterior;
  _d_, M. levator scapulæ; _e_, M. rhomboideus; _f_, M.
  occipitoscapularis; _g_, M. biceps; _h_, M. coracobrachialis; _i_,
  caput longum of M. triceps.]


2. =Muscles of the Brachium or Upper Arm.=

M. clavobrachialis and the pectoralis group (Fig. 65, page 109) lie
partly in this region; they have been described.

=M. coracobrachialis= (Fig. 77, _f_; Fig. 79, _c_).--A very short muscle
covering the inner (medial) surface of the capsule of the
shoulder-joint. It extends from the coracoid process to the proximal end
of the humerus.

_Origin_ (Fig. 78, _h_).--By a round tendon from the tip of the coracoid
process.

_Insertion_ (Fig. 82, _e_) usually by fleshy fibres on an area five to
eight millimeters long and about half as wide, which lies on the medial
side of the humerus parallel with the ridge which runs from the dorsal
end of the lesser tuberosity to the shaft and close to it. The proximal
end of the area is about one centimeter from the proximal end of the
head of the humerus.

_Relations._--Medial surface with the biceps (Fig. 77, _g_), pectoralis
minor (Fig. 65, _o_), and teres major (Fig. 77, _c_). Lateral surface
with the capsule of the shoulder-joint. Dorsal border with the
subscapularis (Fig. 77, _a_) and the long portion of the caput mediale
of the triceps (Fig. 77, _j_).

_Action._--Adducts the humerus.

The part of the coracobrachialis just described is known as the _short_
head. A _long_ head is sometimes found. It is a conical bundle of
fibres of varying size, which arises from the tendon of origin of the
short head. It passes distad into a long and extremely slender tendon,
the insertion of which varies greatly in different individuals. It is
commonly on the humerus in the region of the supracondyloid foramen.

=M. epitrochlearis= or extensor antibrachii longus (Fig. 65, _r_).--A
thin, flat muscle on the inner or medial side of the brachium, from the
lateral surface of the latissimus dorsi (Fig. 65, _q_) to the olecranon
process of the ulna.

_Origin_ from the lateral or outer surface of the ventral border of the
latissimus dorsi (Fig. 65, _q_) near the insertion of the cutaneus
maximus. Fibres are often attached to the teres major and the pectoralis
minor.

_Insertion_ by a flat tendon which is closely connected with that of the
pectoantibrachialis (Fig. 65, _m_) and is continuous with the general
antibrachial fascia, into the caudal border of the cutaneous (dorsal)
surface of the olecranon process of the ulna.

_Relations._--Outer (medial) surface with the integument, the latissimus
dorsi (Fig. 65, _q_), and the cutaneus maximus. Inner (lateral) surface
with the biceps (Fig. 65, _t_), caput longum (Fig. 65, _s_), and caput
mediale (Fig. 77, _j_, _k_) of the triceps.

_Action._--Extends the antibrachium and tends to supinate the hand by
rotating the ulna.

=M. biceps brachii= (Fig. 77, _g_; Fig. 65, _t_).--A thick, fusiform
muscle lying on the front (ventral) surface of the humerus.

_Origin_ (Fig. 76, _c_) by a strong, round tendon from the bicipital
tubercle of the glenoid angle of the scapula, at its coracoid margin.
(In man there is a second head--coracoid head--from the coracoid
process.) The tendon passes through the capsule of the joint and then
along the bicipital groove, which is converted into a canal by a strong
ligament.

_Insertion_ by a rounded tendon (Fig. 87, _b_) on the bicipital
tuberosity of the radius (Fig. 86, _k_).

_Relations._--The tendon of origin passes through the capsule of the
joint, which is covered by a part of the pectoralis minor. The muscle is
then spanned for the middle part of its course by the bicipital arch
(Fig. 65, _t′_), a description of which is given below. Farther distad
it is covered by the clavobrachial (Fig. 65, _k_) and epitrochlearis
(Fig. 65, _r_). At its distal end (Fig. 79, _l′_) the muscle passes
between the pronator teres on the radial side and the conjoined tendon
of the brachialis and clavobrachial (Fig. 79, _i′_) on the other. The
biceps lies throughout most of its length on the ventral surface of the
humerus, and touches along the medial border of its inner surface the
coracobrachialis (Fig. 77, _f_), the teres major, (Fig. 77, _c_), the
intermediate portion of the caput mediale of the triceps (Fig. 77, _k_),
and the short portion (Fig. 77, _l_) of the same. Its lateral border
touches the pectoralis minor (Fig. 65, _o_) and the brachialis (Fig. 79,
_i_).

_Action._--Flexes the forearm, and tends to supinate the hand.

=The bicipital arch= (Fig. 65, _t′_) is a tendinous arch formed over the
biceps muscle. Its outer or lateral pillar is formed by the tendon of
the pectoralis minor (_o_), to which may be added part of the latissimus
(_q_) tendon. Its inner or medial pillar is formed by the conjoined
tendon of the teres major and latissimus dorsi (Fig. 79, _d′_), while
the xiphihumeralis (Fig. 65, _p_), cutaneus maximus (Fig. 62, _b_), and
epitrochlearis (Fig. 65, _r_) are connected with one or the other pillar
or with the muscles composing them. The caudal portion of the deep layer
of the pectoralis major (Fig. 65, _l_) may be connected with the inner
pillar.

=M. brachialis= (Fig. 79, _i_; Fig. 75, _i_).--From the lateral surface
of the humerus to the ulna.

_Origin_ (Fig. 83, _g_, _g′_) from a long V-shaped line two to four
millimeters wide on the lateral surface of the humerus. The apex of the
V is just distad of the teres minor tubercle (_d_). Its dorsal limb
(_g′_) extends along the lateral supracondyloid ridge to a point
opposite the proximal margin of the supracondyloid foramen; its ventral
limb (_g_) extends in the direction of the deltoid ridge to the middle
of the bone. No muscle-fibres take origin between the two limbs. The
fibres converge and end in a flat tendon which joins the tendon of the
clavobrachial (Fig. 79, _k_).

_Insertion_ (Fig. 87, _c_).--The dorsal portion of the depressed rough
area on the lateral surface of the ulna just distad of the semilunar
notch.

_Relations._--Outer surface with the acromiodeltoid (Fig. 75, _f_), the
caput laterale of the triceps (Fig. 75, _h_), the brachioradialis (Fig.
75, _k_), and the proximal end of the extensor carpi radialis longus
(Fig. 75, _l_). Inner surface with the humerus. Medial edge with the
pectoralis major (Fig. 65, _l_) and the biceps (Fig. 77, _g_).

_Action._--Flexor of the antibrachium.

=M. triceps brachii.=--The triceps muscle of the cat, like that of man,
is divisible (as its name indicates) into three main portions. These are
a lateral portion (caput laterale), an intermediate or long portion
(caput longum), and a medial portion (caput mediale). The first two
correspond to the similarly named heads in man; the medial portion falls
into a number of subdivisions whose homologues are uncertain.

  [Illustration: FIG. 79.--DEEP MUSCLES ON THE MEDIAL SIDE OF THE
  HUMERUS.

  _a_, M. supraspinatus; _b_, M. subscapularis; _c_, M.
  coracobrachialis; _d_, M. teres major (_d′_, its tendon); _e_, part of
  M. latissimus dorsi joining the teres major; _f_, cut end of M.
  pectoralis minor; _g_, long part of caput mediale of M. triceps
  brachii; _h_, intermediate part of caput mediale of M. triceps; _i_,
  M. brachialis (_i′_, its tendon); _j_, short part of caput mediale of
  M. triceps; _k_, cut end of M. clavobrachialis; _l_, _l′_, cut ends of
  M. biceps; _m_, M. brachioradialis; _n_, M. extensor carpi radialis
  longus; _o_, M. extensor carpi radialis brevis; _p_, fifth head of M.
  flexor profundus digitorum; _q_, first head of M. flexor profundus
  digitorum. 1, humerus; 2, olecranon; 3, medial epicondyle of humerus.]

=Caput laterale= (anconeus lateralis) (Fig. 75, _h_; Fig. 68, _l_).--The
lateral portion is a flat muscle (most of it subcutaneous) on the
lateral side of the brachium, connecting the proximal end of the humerus
with the olecranon process of the ulna.

_Origin_ (Fig. 81, _h′_).--By a flat tendon from the proximal portion of
the deltoid ridge and the distal border of the teres minor tubercle.

_Insertion_ (Fig. 86, _c_) by a thin, flat tendon into the lateral
border of the dorsal surface of the ulna between a point opposite the
distal margin of the semilunar notch and the proximal end of the
olecranon.

_Relations._--Lateral surface with the integument, and at the proximal
end with the spinodeltoid and acromiodeltoid (Fig. 75, _e_ and _f_).
Medial surface with the brachialis (Fig. 75, _i_), the caput longum
(_g_), the caput mediale, the brachioradialis (_k_), the anconeus (Fig.
80, _l_), and the origins of the extensor carpi radialis longus (Fig.
75, _l_), the extensor communis digitorum (_m_), and the extensor
digitorum lateralis (_n_).

=Caput longum= (anconeus longus) (Fig. 75, _g_; Fig. 68, _k_; Fig. 77,
_i_).--A prismatic, fusiform mass connecting the scapula with the
olecranon.

_Origin_ (Fig. 78, _i_) by a thick, flat tendon from a triangular area
one or two centimeters long at the glenoid end of the scapula on the
glenoid border. The base of the area is about one millimeter from the
margin of the glenoid fossa.

_Insertion_ (Fig. 86, _b_).--The muscle ends in a thick tendon which
passes over the bifurcated ventral end of the olecranon and is inserted
upon the rounded tuberosity which forms the dorsal angle of the
olecranon.

_Relations._--Lateral surface with the caput laterale (Fig. 75, _h_), a
portion of the caput mediale (Fig. 77, _j_ and _k_), the spinodeltoid
(Fig. 75, _e_), the infraspinatus (Fig. 75, _c_), and the integument.
Medial surface with the epitrochlearis (Fig. 65, _r_) and the conjoined
portions of the latissimus dorsi and teres major (Fig. 79, _d′_).
Ventral border with the caput mediale (Fig. 77, _j_ and _k_).

=Caput mediale.=--The medial head consists of three portions (Fig. 79,
_g_, _h_, _j_).

(1) The long portion (anconeus posterior) (Fig. 77, _j_; Fig. 79, _g_;
Fig. 80, _f_).

_Origin_ (Fig. 83, _e_) from a triangular area on the dorsal surface of
the humeral shaft. The base of the area is against the articular head,
and its apex about one-sixth the length of the humerus from the head. It
is between the coracobrachialis and the lateral head of the triceps.

  [Illustration: FIG. 80.--DEEP MUSCLES ON THE LATERAL SURFACE OF THE
  HUMERUS.

  _a_, part of M. supraspinatus; _b_, part of M. infraspinatus; _c_, M.
  teres minor; _d_, M. teres major; _e_, part of M. latissimus dorsi
  joining M. teres major; _f_, long part of caput mediale of M. triceps
  brachii; _g_, cut insertion of M. acromiodeltoideus; _h_, M.
  brachialis; _i_, M. brachioradialis; _j_, intermediate part of caput
  mediale of M. triceps brachii; _k_, M. extensor carpi radialis longus;
  _l_, M. anconeus; _m_, M. extensor communis digitorum. 1, great
  tuberosity of humerus; 2, 3, superficial radial and dorsal
  interosseous branches, respectively, of the radial nerve.]

_Insertion_ (Fig. 86, _a_).--The muscle ends in a long, slender tendon
which passes through the furrow on the ventral angle of the olecranon
and is inserted into an oblique ridge which forms the dorsal limit of
the furrow. The tendon is separated from the floor of the furrow by a
synovial bursa.

(2) The intermediate portion (anconeus internus) (Fig. 77, _k_; Fig. 79,
_h_; Fig. 80, _j_).

_Origin_ (Fig. 82, _g_) by fleshy fibres from a triangular area proximad
of the middle of the dorsomedial surface of the humerus. The length of
the area equals about one-fourth the length of the bone. Its apex points
proximad and is almost continuous with the apex of the area of origin of
the long portion.

_Insertion_ (Fig. 87, _i_) by short tendon-fibres into the medial border
of the ventral and proximal surfaces of the olecranon. It is connected
with the tendon of the long portion.

(3) Short portion (Fig. 79, _j_; Fig. 77, _l_).

_Origin_ (Fig. 82, _h_) from the outer surface of the bony bar which
encloses the supracondyloid foramen of the humerus, as far as the medial
epicondyle.

_Insertion_ (Fig. 87, _e_) by fleshy fibres into the medial border of
the olecranon distad of the tuberosity for the insertion of the caput
longum.

_Relations_ of the caput mediale.--Lateral surface with the caput
laterale (Fig. 75, _h_), the humerus, and the anconeus (Fig. 80, _l_).
Dorsal surface with the caput longum (Fig. 77, _i_), the epitrochlearis
(Fig. 65, _r_), and the teres major (Fig. 79, _d_). Ventral surface with
the biceps (Fig. 77, _g_).

_Action of the Triceps._--The entire triceps group forms a powerful
extensor of the forearm. The short portion of the medial head tends also
to rotate the arm outward, so as to supinate the hand.

=M. anconeus= (Fig. 80, _l_).--A triangular muscle on the outside of the
elbow-joint from the humerus to the ulna.

_Origin_ (Fig. 83, _i_).--An irregularly triangular area at the distal
end of the dorsal surface of the humerus. The area of origin is limited
laterally by the sharp lateral supracondyloid ridge. It sometimes
extends onto the lateral epicondyle.

  [Illustration: FIG. 81.--VENTRAL SURFACE OF HUMERUS, WITH THE AREAS OF
  ATTACHMENT OF MUSCLES.

  FIG. 82.--MEDIAL SIDE OF HUMERUS, WITH THE AREAS OF ATTACHMENT OF
  MUSCLES.

  FIG. 83.--DORSAL SURFACE OF THE LEFT HUMERUS, WITH THE AREAS OF
  ATTACHMENT OF MUSCLES.

  Fig. 81.--_a_, M. subscapularis; _b_, M. supraspinatus; _c_, Mm. teres
  major and latissimus dorsi; _d_, M. pectoralis minor; _e_, deep layer
  of M. pectoralis major; _f_, superficial layer of M. pectoralis major;
  _g_, M. acromiodeltoideus; _h_, M. spinodeltoideus; _h′_, caput
  laterale of M. triceps; _i_, M. brachialis; _j_, second portion of M.
  brachialis; _k_, M. extensor carpi radialis longus; _l_, M. extensor
  carpi radialis brevis; _m._ M. extensor communis digitorum; _n_, M.
  extensor lateralis digitorum; _o_, M. extensor carpi ulnaris; _p_,
  short portion of caput mediale of M. triceps; _q_, M. pronator teres;
  _r_, M. palmaris longus; _s_, third and fourth parts of M. flexor
  profundus digitorum; _t_, M. flexor carpi radialis; _u_, second head
  of M. flexor profundus digitorum.

  Fig. 82.--_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M.
  pectoralis minor; _d_, long portion of caput mediale of M. triceps;
  _e_, M. coracobrachialis; _f_, Mm. teres major and latissimus dorsi;
  _g_, intermediate portion of caput mediale of M. triceps; _h_, deep
  layer of M. pectoralis major; _i_, superficial layer of M. pectoralis
  major; _j_, M. anconeus; _k_, short portion of caput mediale of M.
  triceps; _l_, M. pronator teres; _m_, M. flexor carpi radialis; _n_,
  second head of M. flexor profundus digitorum; _o_, third and fourth
  heads of M. flexor profundus digitorum; _p_, M. palmaris longus; _q_,
  M. flexor carpi ulnaris.

  Fig. 83.--_a_, M. supraspinatus; _b_, M. subscapularis; _c_, M.
  infraspinatus; _d_, M. teres minor; _e_, long portion of caput mediale
  of M. triceps; _f_, M. coracobrachialis; _g_, _g′_, M. brachialis;
  _h_, intermediate portion of caput mediale of M. triceps; _i_, M.
  anconeus; _j_, short portion of medial head of M. triceps; _k_, M.
  pronator teres; _l_, second and third heads of M. flexor profundus
  digitorum; _m_, M. palmaris longus; _n_, M. extensor carpi ulnaris.]

_Insertion_ (Fig. 86, _d_).--The lateral surface of the ulna from the
distal margin of the semilunar notch to the proximal end of the
olecranon. The muscle covers the capsule of the joint and is closely
adherent to it.

_Relations._--Outer (dorsal) surface with the caput laterale (Fig. 75,
_h_) and the intermediate portion (Fig. 80, _j_) of the caput mediale.
Inner surface with the bones and the capsule of the joint.

_Action._--Keeps the capsule tense and probably rotates the ulna
slightly so as to pronate the hand.


3. =Muscles of the Antibrachium or Forearm.=


_Fascia of the Forearm._--The muscles of the forearm are not in contact
with the skin, but are covered by the strong =antibrachial fascia=. This
consists of two layers. The =superficial= one is a continuation of the
general subcutaneous fascia of the arm; it covers the forearm as a
continuous sheet which becomes thinner distad, and is finally lost near
the wrist. The =deep= layer forms a dense, tendinous sheet which is
closely applied to the muscles. It begins partly as a continuation of
the general fascia of the arm, partly from the tendons of the triceps
and epitrochlearis muscles. The sheet is attached to the dorsal surface
of the ulna, between the extensor carpi ulnaris and the first head of
the flexor profundus digitorum. It surrounds the forearm as a continuous
sheath. On the lateral surface it dips between the extensor muscles,
becoming closely attached to them and forming a partial sheath for each;
it is attached with special firmness to their tendons. On the medial
side of the arm the fascia passes smoothly over the flexors without
dipping between them; it is continuous, however, with the border of the
pronator teres, and distad of this muscle it is firmly attached to the
radius.

At the wrist the fascia becomes attached to the longitudinal ridges on
the dorsal surface of the head of the radius, bridging thus the
intervening grooves and holding the tendons in place between the ridges.
The fascia then continues to form the dorsal fascia of the hand. On the
ventral side of the wrist the fascia becomes thickened to form a strong
=transverse ligament= (Fig. 77, 1), which is attached at its radial and
ulnar ends to the carpus, and which holds in place the tendons of the
flexor muscles. Distad of the transverse ligament the fascia spreads out
in the palm of the hand, and becomes united with the fibrous pad which
is situated here. On the fingers the fascia becomes attached to the
phalanges, forming tendinous sheaths, the so-called =vaginal ligaments=,
for the flexor muscles. Near the base and the head of the first phalanx
strong, narrow, ring-like bands, the =annular ligaments= (Fig. 88, 2),
are formed in these sheaths; these surround and bind down the tendons of
the flexor muscles.


A. MUSCLES ON THE ULNAR AND DORSAL SIDE OF THE FOREARM (extensors and
supinators) (Fig. 75, p. 158).

=M. brachioradialis= or supinator longus (Fig. 75, _k_; Fig. 77,
_n_).--This is a ribbon-like muscle lying on the lateral side of the
brachium and the ventrolateral border of the antibrachium just beneath
the superficial fascia. It connects the humerus and the radius.

_Origin._--By a thin tendon from about the middle fifth of the dorsal
border of the humerus, or sometimes proximad of the middle. The muscle
curves over the outer surface of the brachialis (Fig. 75, _i_), to which
it is closely applied, and runs along the lateral border of the
antibrachium to its insertion.

_Insertion_ by a short tendon into the ridge which forms the ventral
limit of the groove on the outer surface of the styloid process of the
radius and upon the adjacent ligaments.

_Relations._--Outer surface with the integument, and at the proximal end
with the caput laterale of the triceps (Fig. 75, _h_). Inner surface
with the brachialis (_i_), the extensor carpi radialis longus (_l_) and
brevis, and the extensor communis digitorum (_m_).

_Action._--Supinator of the hand.

=M. extensor carpi radialis longus= (Fig. 75, _l_; Fig. 77, _o_).--This
lies along the radial side of the forearm, and connects the humerus and
the second metacarpal.

_Origin_ (Fig. 81, _k_) from the middle portion of the lateral
supracondyloid ridge between the origin of the brachialis (_j_) and the
anconeus. About the middle of the forearm the muscle ends in a slender
tendon (Fig. 84, _e_) which passes through the groove on the radial side
of the dorsal surface of the distal end of the radius.

_Insertion_ (Fig. 84, _c_).--The tendon passes across the carpus and is
inserted onto the dorsal surface of the base of the second metacarpal on
the radial side just distad of the groove for the radial artery.

_Relations._--Outer surface at the proximal end with the caput laterale
of the triceps (Fig. 75, _h_), farther distad with the integument and
the brachioradialis (_k_); the distal tendon with the extensor pollicis
brevis (Fig. 84, _d_). Radial surface with the brachialis (Fig. 75, _i_)
and the integument. Ulnar surface with the extensor carpi radialis
brevis (Fig. 77, _p_), and near the proximal end with the extensor
communis digitorum (Fig. 75, _m_).

_Action._--Extensor of the hand.

=M. extensor carpi radialis brevis= (Fig. 77, _p_).--A slender muscle
from the humerus to the third metacarpal.

_Origin_ (Fig. 81, _l_) from the distal part of the lateral
supracondyloid ridge distad of the extensor longus. Near the carpus the
muscle ends in a slender tendon which passes through the groove with the
extensor longus tendon. The tendon then diverges from the extensor
longus and has its

_Insertion_ (Fig. 84, _f_) into the radial side of the dorsal surface of
the base of the third metacarpal.

_Relations._--Outer surface with the extensor longus (Fig. 77, _o_), the
integument, and distad with the extensor pollicis brevis (Fig. 84, _d_).
Radial surface with the extensor longus. Ulnar surface with the extensor
communis digitorum (Fig. 75, _m_) and the extensor brevis pollicis.
Inner surface with the pronator teres (Fig. 77, _q_), supinator (Fig.
85, _b_), and extensor brevis pollicis (Fig. 85, _a_).

_Action._--Extensor of the hand.

  [Illustration: FIG. 84.--ARRANGEMENT OF THE TENDONS ON THE BACK OF THE
  HAND.

  _a_, M. extensor communis digitorum; _b_, M. extensor lateralis
  digitorum; _c_, M. extensor indicis; _d_, M. extensor brevis pollicis;
  _e_, M. extensor carpi radialis longus; _f_, M. extensor carpi
  radialis brevis; _g_, M. extensor carpi ulnaris; _h_, tendons of the
  interossei. 1, transverse ligament of the wrist.]

=M. extensor digitorum communis= (Fig. 75, _m_).--A slender muscle from
the lateral supracondyloid ridge of the humerus to the phalanges of the
second, third, fourth, and fifth digits.

_Origin_ (Fig. 81, _m_).--The distal surface of the lateral
supracondyloid ridge dorsad of the origin of the extensor carpi radialis
brevis.

At the junction of the middle and distal thirds of the radius the muscle
passes into a large, flat tendon (Fig. 75, _m′_) which passes through
the groove on the middle of the dorsal surface of the distal end of the
radius. The groove is converted into a canal by a strong transverse
ligament. The tendon divides near the groove into four portions (Fig.
84, _a_) which diverge and pass to the four ulnar digits.

_Insertions._--Each division of the tendon as it passes over the dorsal
surface of the first phalanx has its border connected by strong fascia
to the dorsal surface of the phalanx. It finally passes through the
groove at the distal end of the first phalanx and is inserted mostly
into the base of the second phalanx; a portion continues distad to be
inserted into the third phalanx.

_Relations._--Outer surface with the integument and at the origin with
the caput laterale (Fig. 75, _h_) of the triceps. Radial surface with
the extensor longus (_l_) and extensor brevis. Ulnar surface with the
extensor digitorum lateralis (_n_). Inner surface with the supinator
(Fig. 85, _b_) and the extensor pollicis brevis (Fig. 85, _a_).

_Action._--Extensor of the four ulnar digits.

=M. extensor digitorum lateralis= (Fig. 75, _n_). (This corresponds in
position to the extensor digiti quinti proprius of man.)

_Origin_ (Fig. 81, _n_) from the lateral supracondyloid ridge of the
humerus distad of the origin of the extensor communis.

The muscle passes along the ulnar border and dorsal surface of the
forearm between the extensor communis (Fig. 75, _m_) and the extensor
carpi ulnaris (_o_). Near the carpus it ends in a tendon (_n′_), which
divides immediately into three or four (Fig. 84, _b_). These pass
through the groove on the ulnar side of the dorsal surface of the
radius and diverge to the digits lying beneath the extensor communis
tendon.

_Insertion_ (Fig. 84, _b_).--The three tendons on the ulnar side join
the ulnar sides of the tendons of the extensor communis (_a_) at their
insertions. The radial of the four tendons (not always present) joins
the tendon of the extensor indicis (_c_) and may also give a branch to
the radial side of the base of the first phalanx of the third digit.

_Relations._--Outer surface with the integument. Radial border with the
extensor communis digitorum (_m_); ulnar border with the extensor carpi
ulnaris (_o_). Inner surface with the supinator (Fig. 85, _b_) and the
extensor brevis pollicis (Fig. 85, _a_); distad with the extensor
indicis (Fig. 85, _c_).

_Action._--Extensor of the four ulnar digits.

=M. extensor carpi ulnaris= (Fig. 75, _o_).

_Origin._--(1) By a short, broad tendon from the distal portion of the
lateral epicondyle of the humerus (Fig. 81, _o_) distad of the origin of
the extensor lateralis, and (2) by a smaller tendon from the ulna at the
dorsal tip of the semilunar notch (Fig. 86, _e_).

The muscle passes along the ulnar side of the forearm dorsad of the
extensor digitorum lateralis (_n_). It ends near the junction of the
middle and distal thirds of the forearm in a large, flat tendon (_o′_)
which is closely adherent to the ligaments of the wrist and which passes
over the distal end of the ulna to its

_Insertion_ into the tubercle on the ulnar side of the base of the fifth
metacarpal (Fig. 84, _g_).

_Relations._--Outer surface with the integument. Radial (or ventral)
border with the extensor digitorum lateralis (Fig. 75, _n_); ulnar (or
dorsal) border with the flexor profundus digitorum (_q_). Inner surface
with the radius, the extensor indicis (Fig. 85, _c_), and the extensor
pollicis brevis (Fig. 85, _a_).

_Action._--Indicated by its name.

=M. extensor indicis (proprius)= (Fig. 85, _c_; Fig. 75, _p_) (includes
extensor pollicis longus also).

_Origin_ (Fig. 86, _f_) by short, fleshy fibres from the lateral surface
of the ulna between the semilunar notch and the junction of the third
and fourth (distal) fourths.

The muscle-fibres pass obliquely distad and toward the radial side and
join the tendon (Fig. 85, _c′_), which runs nearly the whole length of
the radial surface.

_Insertion_ (Fig. 84, _c_).--The tendon passes through the groove on the
ulnar side of the dorsal surface of the base of the radius and divides
into two. Both of these usually go to the base of the second phalanx of
the second digit, but one may pass to the pollex, or there may be three
divisions going to the first three digits.

  [Illustration: FIG. 85.--DEEP MUSCLES ON THE EXTENSOR SURFACE OF THE
  RADIUS AND ULNA.

  _a_, M. extensor brevis pollicis (_a′_, its tendon); _b_, M.
  supinator; _c_, M. extensor indicis (_c′_, its tendon); _d_, tendon of
  M. extensor carpi radialis brevis; _e_, tendon of M. extensor carpi
  radialis longus. 1, humerus; 2, olecranon; 3, styloid process of ulna;
  4, distal end of radius; 5, head of radius.]

_Relations._--Outer surface with the integument, the extensor carpi
ulnaris (Fig. 75, _o_), and the extensor digitorum lateralis (Fig. 75,
_n_). Dorsal border with the flexor profundus digitorum (Fig. 75, _q_).
Inner surface with the extensor brevis pollicis (Fig. 85, _a_).

_Action_ as indicated by the name.

=M. supinator= (Fig. 85, _b_).--A flat muscle wrapped spirally about the
proximal end of the radius.

_Origin_ by a short, strong tendon from the lateral side of the annular
ligament of the radius and by tendinous fibres from the radial
collateral ligament passing from the humerus to the radius. From the
tendon of origin the fibres diverge, passing toward the radial side and
distad.

_Insertion_ (Fig. 86, _g_).--The dorsal and part of the ventral surface
of the proximal two-fifths of the radius to within five millimeters of
the articular face of the head.

_Relations._--Outer surface with the extensor carpi radialis brevis,
extensor communis digitorum (Fig. 75, _m_), and extensor lateralis
digitorum (Fig. 75, _n_). Radial border with the pronator teres (Fig.
77, _q_). Inner surface with the radius.

_Action._--Supinator of the hand.

  [Illustration: FIG. 86.--LATERAL OR EXTENSOR SURFACE OF RADIUS AND
  ULNA, WITH THE AREAS OF ATTACHMENT OF MUSCLES.

  _a_, long portion of caput mediale of M. triceps; _b_, caput longum of
  M. triceps; _c_, caput laterale of M. triceps; _d_, M. anconeus; _e_,
  M. extensor carpi ulnaris; _f_, M. extensor indicis; _g_, M.
  supinator; _h_, M. extensor brevis pollicis; _i_, M. pronator teres;
  _j_, M. flexor profundus digitorum; _k_, M. biceps.]

=M. extensor brevis pollicis= or extensor ossis metacarpi pollicis (Fig.
85, _a_) (includes M. abductor longus pollicis of man).

_Origin_ (Fig. 86, _h_) by fleshy fibres from the ventral half of the
lateral surface of the shaft of the ulna from the semilunar notch to the
styloid process; from the ulnar half of the dorsal surface of the radius
from the bicipital tubercle to a short distance distad of the middle of
the bone; and from the interosseous membrane between these two areas.
The fibres converge to form a strong, flat tendon (Fig. 84, _d_) which
passes obliquely over the tendons of the extensor carpi radialis longus
(_e_) and brevis (_f_) to its

_Insertion_ into the radial side of the base of the first metacarpal.
The radial sesamoid bone of the wrist is imbedded in the tendon at its
insertion.

_Relations._--Outer surface with the extensor carpi radialis brevis, the
extensor communis digitorum (Fig. 75, _m_), extensor lateralis digitorum
(Fig. 75, _n_), and extensor indicis (Fig. 85, _c_). Inner surface with
the radius and ulna, and distad with the tendons of the two extensores
carpi radiales (Fig. 84, _e_ and _f_).

_Action._--Extends and abducts the pollex.


B. MUSCLES ON THE RADIAL AND VENTRAL SIDE OF THE FOREARM (flexors and
pronators).

=M. pronator teres= (Fig. 77, _q_).

_Origin_ (Fig. 82, _l_) by a short strong tendon from the extremity of
the medial epicondyle of the humerus.

_Insertion_ (Fig. 86, _i_) by fleshy fibres and short tendinous fibres
along the medial border of the radius, at its middle. The radial edge of
the muscle is continuous with the strong deep layer of the antibrachial
fascia.

_Relations._--Outer surface with the superficial fascia. Radial border
with the tendon of the biceps (Fig. 79, _l′_), with the extensor carpi
radialis brevis (Fig. 77, _p_), and the supinator (Fig. 85, _b_). Ulnar
border with the flexor carpi radialis (Fig. 77, _r_) and part of the
flexor profundus digitorum (Fig. 77, _u_).

_Action._--Pronates the hand by rotating the radius.

=M. flexor carpi radialis= (Fig. 77, _r_).--A slender fusiform muscle.

_Origin_ (Fig. 82, _m_) from the tip of the medial epicondyle of the
humerus.

_Insertion._--The slender tendon passes through a deep groove between
the os magnum and the first metacarpal. The groove is converted into a
canal by the overlying tendons and muscles. The tendon is finally
inserted into the bases of the second and third metacarpals.

_Relations._--Outer surface with the pronator teres (Fig. 77, _q_), the
superficial fascia, and the third head of the flexor profundus (_u_).
Radial border with the pronator teres (_q_). Ulnar border with the third
and fourth heads of the flexor profundus. Inner surface with the ulna
proximad and the fifth head of the flexor profundus (_u′_) distad.

_Action_ indicated by the name.

=M. palmaris longus= (Fig. 77, _s_).--A flat fusiform muscle beneath
the fascia on the medial border of the forearm.

_Origin_ (Fig. 82, _p_) by a short flat tendon from the distal part of
the medial surface of the medial epicondyle of the humerus.

About one centimeter from the wrist the muscle ends in a flat tendon
which passes through the transverse ligament and divides on the hand
into four or five (or sometimes only three) tendons (Fig. 77, _s′_)
which diverge to the insertions. The ulnar portion of the flexor
sublimis digitorum (Fig. 77, _x_) takes origin from the common tendon
before its division.

_Insertion._--Each tendon except the first gives off a branch which
spreads out in the trilobed pad in the palm. The middle two of these may
be traced to the integument covering the pad. The tendon is then
inserted (Fig. 88, _a_) near the base of the first phalanx onto the
outer surface of the perforated portion of the flexor sublimis tendon
(_b_, _b′_) at its side, except that to the thumb, which divides near
its distal end into two which are inserted into the sesamoid bones at
the base of the first phalanx. The tendons of insertion are closely
united to the fibrous pulley-ring at the base of the first phalanx, and
each may send a slip to the base of the phalanx at either side of the
ring.

_Relations._--Outer surface with the superficial fascia and one head of
the flexor sublimis (Fig. 77, _x_). Radial border with the flexor carpi
radialis. Ulnar border with the flexor carpi ulnaris and a part of the
flexor profundus digitorum. Inner surface with the flexor carpi
radialis (_r_), the flexor carpi ulnaris (_t_), the flexor profundus
digitorum (_u_), and the radial head of the flexor sublimis digitorum.

_Action._--Flexor of the first phalanx of each of the digits.

=M. flexor carpi ulnaris= (Fig. 77, _t_, _t′_).

_Origin._--There are two heads. The first or humeral head (_t′_) takes
origin in common with the second part of the flexor profundus from the
median surface of the distal end of the humerus just distad of the
medial epicondyle (Fig. 82, _q_). The second or ulnar head (_t_) takes
origin by fleshy fibres from the lateral surface of the olecranon and
from the dorsal border of the ulna from the olecranon to a point distad
of the semilunar notch (Fig. 87, _f_). The two heads join proximad of
the middle of the forearm. The muscle passes obliquely across the
ventral surface of the forearm to its

_Insertion_ by fleshy and tendinous fibres into the proximal surface of
the pisiform bone.

_Relations._--Outer surface with the integument and the palmaris longus
(Fig. 77, _s_). Inner surface and ulnar border with the flexor profundus
digitorum.

_Action_ indicated by the name.

=M. flexor sublimis digitorum= (or perforatus).--This muscle is in two
parts, which are given a common name only because of the similar
structure and insertions of their tendons.

The =ulnar part= (Fig. 77, _x_) is a conical muscle taking origin from
the outer surface of the tendon and muscle of the palmaris longus and
from the adjacent ligament. It gives rise to two or three tendons (Fig.
88, _b_) which arise from distinct slips of the muscle; these pass to
the ulnar two or three digits. That passing to the fourth or fifth digit
receives an accessory slip from a small mass of fibres attached to the
transverse ligament on the radial side of the palmaris tendon.

The =radial part= is a small flat triangular muscle which takes origin
from the outer surface of the tendon formed by the junction of the
tendons of the first and second parts of the flexor profundus. It
divides into two slips, each giving rise to a tendon. These tendons
(Fig. 88, _b′_) pass to the second and third digits. That to the third
digit may divide into two, one of which goes to the fourth digit.

Each of the four tendons (Fig. 88, _b_ and _b′_) is perforated by a
tendon of the flexor profundus (Fig. 88, _c_) as it passes through the
fibrous pulley-ring at the base of the first phalanx. It then continues
beneath the flexor profundus tendon through the second pulley-ring (2)
and is inserted into the base of the second phalanx.

_Relations._--Outer surface of the ulnar part with the integument; inner
surface with the palmaris longus (Fig. 77, _s_). Outer surface of the
radial part with the palmaris longus; inner surface with the flexor
profundus.

_Action._--Flexor of the second phalanx of digits 2-5.

=M. flexor profundus digitorum= (or perforans).--This arises by five
heads, the tendons of which join one another at the wrist to make the
strongest and deepest of the flexor tendons.

The _first_ or _ulnar head_ has _origin_ (Fig. 87, _g_) from the dorsal
half of the medial (radial) surface of the ulna from the proximal lip of
the semilunar notch to within a centimeter of the styloid process. Its
fibres converge to a large flat tendon which forms the lateral (ulnar)
and superficial part of the common tendon.

  [Illustration: FIG. 87.--RADIUS AND ULNA, Medial or Flexor Side, with
  M. pronator quadratus and the Areas of Attachment of Other Muscles.

  _a_, M. pronator quadratus; _b_, tendon of M. biceps; _c_, conjoined
  tendon of M. brachialis and M. clavobrachialis; _d_, insertion of
  caput longum of M. triceps; _e_, insertion of short portion of caput
  mediale of M. triceps; _f_, origin of M. flexor carpi ulnaris; _g_,
  origin of first head of M. flexor profundus digitorum; _h_, origin of
  fifth head of M. flexor profundus digitorum; _i_, intermediate portion
  of caput mediale of M. triceps.]

The _second head_ has _origin_ (Fig. 82, _n_) from the distal end of the
medial epicondyle of the humerus between the flexor ulnaris and the
third and fourth heads of the profundus. It may be very closely attached
to these muscles at their origins. Its tendon joins the radial border of
the tendon of the first head. From this junction the radial part of the
flexor sublimis arises.

The _third head_ (Fig. 77, _u_) has _origin_ (Fig. 82, _o_) by a strong
tendon from the medial epicondyle of the humerus, between the palmaris
(_p_) and flexor radialis (_m_). Its tendon forms the radial part of the
common tendon.

The _fourth head_ has _origin_ by a strong tendon from the medial
epicondyle of the humerus just ventrad of the origin of the second head
and the flexor ulnaris, to which many of its fibres are attached. Its
tendon forms the middle and superficial part of the common tendon.

The _fifth_ or _radial head_ (Fig. 75, _q_; Fig. 77, _u′_) has _origin_
(Fig. 87, _h_) from the middle third of the ventral surface of the shaft
of the radius over an area limited by two oblique bony ridges; from the
adjacent parts of the interosseous membrane; and from the ventral part
of the medial surface of the shaft of the ulna between a point about two
centimeters distad of the semilunar notch and the junction of the middle
and distal thirds of the shaft. Its very thick tendon forms the middle
and deep part of the common tendon.

The common tendon (Fig. 88, _c′_) covers the carpus and metacarpus
ventrally. It divides into five tendons (_c_) which pass to the five
digits and are _inserted_ into the bases of the terminal phalanges.
Those of the first four digits perforate the tendon of the flexor
sublimis (_b_) at the base of the first phalanx of each digit. At the
same place each passes through a fibrous pulley-ring attached to the
base of the phalanx. Each then passes through a second pulley-ring (2)
near the head of the phalanx and is finally inserted into the base of
the terminal phalanx.

_Relations._--Outer surface with the pronator teres (Fig. 77, _q_),
flexor carpi radialis (Fig. 77, _r_), palmaris longus (_s_), flexor
carpi ulnaris (_t_), integument, and extensor carpi ulnaris (Fig. 75,
_o_). Inner surface with the radius, ulna, interosseous membrane and
pronator quadratus (Fig. 87, _a_).

_Action._--Flexor of all the digits.

  [Illustration: FIG. 88.--ARRANGEMENT OF THE TENDONS of M. palmaris
  longus, M. flexor sublimis digitorum, and M. flexor profundus
  digitorum, with Mm. lumbricales.

  The integument, fibrous pads, and the palmaris longus (except the ends
  of its tendons) have been removed; the flexor sublimis has been cut.
  _a_, cut ends of tendons of M. palmaris longus; _b_, tendons of M.
  flexor sublimis digitorum, ulnar division; _b′_, radial part of M.
  flexor sublimis digitorum; _c_, tendons of M. flexor profundus
  digitorum (_c′_, the common tendon); _d_, M. abductor digiti quinti;
  _e_, M. flexor brevis digiti quinti; _f_, Mm. lumbricales (_f′_, their
  tendons). 1, transverse ligament of wrist; 2, annular ligaments.]

=M. pronator quadratus= (Fig. 87, _a_).--A thick quadrangular muscle
whose fibres run obliquely between the distal ends of the ulna and
radius.

_Origin_ by fleshy fibres from about the distal half of the ventral
(flexor) surface or border of the ulna and from the interosseous
membrane adjacent to the area. The fibres pass obliquely distad toward
the radial side to their

_Insertion_ by fleshy fibres into the ventral (flexor) surface of the
radius distad of the area of origin of the fifth head of the profundus.

_Relations._--Outer surface with the flexor profundus. Inner surface
with the radius, ulna, and interosseous membrane.

_Action_ as indicated by the name.


4. =Muscles of the Hand.=


A. BETWEEN THE TENDONS.--=Mm. lumbricales= (Fig. 88, _f_, _f′_).--Four
small muscles in the palm of the hand.

_Origin_ by fleshy fibres from the outer (palmar) surface of the tendon
common to the ulnar four parts of the profundus (_c′_).

_Insertion_ (_f′_).--The four slips are flat at their origin. Each
becomes cylindrical and curves about the base of one of the four ulnar
digits and is inserted into the radial side of the base of the first
phalanx close to its ventral border.

  [Illustration: FIG. 89.--DEEP MUSCLES OF THE PALM OF THE HAND.

  _a_, M. flexor brevis pollicis; _b_, M. adductor pollicis; _c_, M.
  interosseus of second digit (M. flexor brevis digiti secundi); _d_, M.
  adductor digiti secundi; _e_, M. interosseus of third digit; _f_, M.
  interosseus of fourth digit; _g_, M. opponens digiti quinti; _h_, M.
  interosseus of fifth digit (M. flexor brevis digiti quinti); _i_, M.
  abductor digiti quinti. 1-5, the digits in order.]

_Action._--Bend the digits toward the radial side.


B. MUSCLES OF THE THUMB.--=M. abductor brevis pollicis= (Fig. 77, _w_)
(includes also the opponens pollicis of man).--A very minute, probably
rudimentary muscle.

_Origin_ from the transverse ligament (1) which connects the prominent
fibrous, hairless projection that lies over the pisiform bone with the
radial border of the head of the radius. The muscle passes radiodistad
and ends in a very slender tendon, the insertion of which is into the
base of the first phalanx of the thumb.

=M. flexor brevis pollicis= (Fig. 89, _a_).

_Origin_ by fleshy fibres from the adjacent borders of the os magnum and
scapholunar bones and from the fascia which bridges the intervening
groove for the flexor carpi radialis.

_Insertion_ by a short tendon into the base of the first phalanx of the
pollex.

_Action._--Flexor of the thumb.

=M. adductor pollicis= (Fig. 89, _b_).

_Origin_ by fleshy fibres from the ventral border of the os magnum. It
curves about the base of the first metacarpal on its ulnar side to its
insertion.

_Insertion_ by fleshy fibres into the base of the first phalanx of the
pollex on its ulnar side.


C. MUSCLES LYING BETWEEN THE METACARPALS.--=Mm. interossei= (Fig.
89).--Small stout muscles lying on the palmar surfaces of the
metacarpals of the second, third, fourth, and fifth digits.

_Origin_ by fleshy fibres from the ventral or lateral surfaces of the
bases of the metacarpals. Near the distal end of the metacarpal each
divides into two masses which pass onto the lateral surfaces of the
metacarpal, so as to leave the ventral surface of the distal end
exposed.

_Insertion_ partly onto the lateral surfaces of the base of the first
phalanx and its sesamoids, and partly by a slender tendon (Fig. 84, _h_)
which is continued dorsad to join the extensor tendon of the digit.


D. SPECIAL MUSCLES OF THE SECOND DIGIT (THE INDEX).--=M. flexor brevis
digiti secundi= (or indicis).--This name may be applied to M.
interosseus of the second digit (Fig. 89, _c_).

=M. abductor digiti secundi.=--This name might be applied to a portion
of the interosseus of the second digit which is sometimes differentiated
from the remainder.

_Origin_ from the radial and ventral surfaces of the base of the second
metacarpal, and from the ventral surface of the trapezium.

_Insertion_ into the radial side of the base of the first phalanx of the
second digit and into its sesamoid.

=M. adductor digiti secundi= (Fig. 89, _d_).

_Origin_ from the ventral surface of the os magnum.

_Insertion_ into the ulnar side of the base of the first phalanx of the
second digit.


E. SPECIAL MUSCLES OF THE FIFTH DIGIT.--=M. abductor digiti quinti=
(Fig. 89, _i_).--A thick, small, conical bundle.

_Origin_ from the distal surface of the pisiform bone and from the
transverse ligament on the ulnar side of the pisiform. It ends in a
slender tendon which runs along the ulnar side of the fifth metacarpal
to its

_Insertion_ into the ulnar side of the base of the first phalanx of the
fifth digit.

=M. flexor brevis digiti quinti= (Fig. 89, _h_; Fig. 88, _e_).--This
covers the ventral surface of the fifth metacarpal, and is really the
interosseus of this digit.

_Origin_ by fleshy fibres from the ventral surface of the base of the
fifth metacarpal; from the ventral process of the unciform bone, and
from the transverse ligament proximad of the fifth metacarpal.

_Insertion_ by fleshy fibres into the ventral border of the proximal end
of the first phalanx of the fifth digit.

=M. opponens (adductor) digiti quinti= (Fig. 89, _g_).

_Origin_ by a flat tendon from the ventral surface of the os magnum on
the ulnar side of the adductor pollicis (_b_). It passes toward the
ulnar side and distad, the fibres diverging to their

_Insertion_ (1) into nearly the whole of the radial surface of the fifth
metacarpal, (2) into the base of its first phalanx.


V. MUSCLES OF THE PELVIC LIMBS.


=1. Muscles of the Hip.=


A. ON THE LATERAL SURFACE OF THE HIP.


=Fascia of the Thigh.=--After the removal of the superficial fascia with
its fat and blood-vessels, there is seen a strong glistening fascia, the
=fascia lata= (Fig. 68, _z_, page 117), covering the vastus lateralis
muscle over the dorsal half of the thigh. Ventrally it dips between the
vastus lateralis and the biceps femoris and, becoming gradually thinner,
is lost on the surface of the former muscle. Passing over the dorsal
border of the thigh, it extends beneath the sartorius and is attached to
the dorsal border of the vastus medialis. Toward its distal end the
fascia is continuous with the tendon of the biceps femoris and dorsad
with the border of the sartorius muscle, while between these points it
is united with the tendon of the vastus lateralis; it thus gains
insertion into the patella. At its proximal end the fascia receives the
insertion of the tensor fasciæ latæ (Fig. 68, _r_).

=M. tensor fasciæ latæ= (Fig. 68, _r_, page 117; Fig. 92, _a_).--The
tensor fasciæ latæ is a thick triangular muscle which may be recognized
by its insertion into the proximal end of the fascia lata (Fig. 68, _z_;
Fig. 92, _a′_).

_Origin_ by fleshy fibres as a thick triangular prism from the outer
margin of the ventral border of the ilium craniad of the auricular
impression and from the fascia covering the ventral border of the
gluteus medius (Fig. 90, _b_) over its cranial half. The caudal border
of the muscle may be continuous with the cranial border of the gluteus
maximus. The muscle spreads out in a fan-like manner, covering the
proximal third of the dorsal surface of the thigh. The cranial fibres
pass farther distad than the others.

_Insertion_ into the fascia lata (Fig. 68, _z_) along an irregular line
which begins caudad at the base of the great trochanter and ends on the
cranial side of the thigh at the junction of the first and second
thirds.

_Relations._--Outer surface with the cutaneus maximus (Fig. 62, _b_,
page 94) and craniad with the sartorius (Fig. 68, _q_). Cranial border
with the sartorius (_q_); caudodorsal border with the gluteus medius
(Fig. 90, _b_). Inner surface with the gluteus medius, the rectus
femoris (Fig. 92, _b_), and the vastus lateralis (Fig. 90, _d_).

_Action_ indicated by the name. It also assists the quadriceps femoris
in extending the leg.

=M. gluteus maximus.=--The gluteus maximus is a rather small
quadrangular muscle in the angle between the gluteus medius (Fig. 90,
_b_) and the caudal vertebræ.

_Origin_ (Fig. 163, 3, page 401) by fleshy fibres from the tips of the
transverse processes of the last sacral and the first caudal vertebræ,
from the fascia covering the spinous muscles dorsad of the transverse
processes of these vertebræ, and from the fascia covering the gluteus
medius. The muscle passes laterad and slightly caudad to its

_Insertion_ by tendon and muscle-fibres into a tubercle on the caudal
side of the great trochanter at the middle of its distal end, and for a
few millimeters into the ridge which continues distad from this
tubercle.

_Relations._--Outer surface with the caudofemoralis (Fig. 68, _s_, page
117), the superficial fascia, and a few fibres of the cutaneus maximus.
Inner surface with the abductor caudæ internus, the tenuissimus (Fig.
90, _g_), the great sciatic nerve (Fig. 163, _a_), the obturator
internus (Fig. 90, _e_), the gluteus medius (Fig. 90, _b_), the gemellus
superior, and the pyriformis (Fig. 163, 7). Cranial border with the
gluteus medius and the tensor fasciæ latæ. Caudal border with the
caudofemoralis (Fig. 68, _s_).

_Action._--Abducts the thigh.

=M. gluteus medius= (Fig. 90, _b_).--The gluteus medius is a very large
triangular muscle which connects the ilium and the sacrum with the great
trochanter (1).

_Origin_ by fleshy fibres (1) from the superficial sacral fascia; (2)
from the lateral surface of the fascia which covers the surface of the
supraspinous extensor muscles of the tail; (3) from the fascia
intervening between it and the tensor fasciæ latæ; (4) by tendon fibres
from the dorsal half of the crest of the ilium and its dorsal border,
and the dorsal half of the lateral surface craniad of the auricular
impression; and (5) from the tips of the transverse processes of the
last sacral and the first caudal vertebræ. The fibres converge to a
strong internal tendon.

_Insertion_ into the proximal end of the great trochanter.

_Relations._--Outer surface with the gluteus maximus and tensor fasciæ
latæ, and between these with the strong fascia lying beneath the
cutaneus maximus muscle. Inner surface with the gluteus minimus, the
pyriformis, and the gemellus superior. Cranial border with the tensor
fasciæ latæ. Caudal border with the gluteus maximus.

_Action._--Abducts the thigh.

=M. pyriformis= (Fig. 163, 7).--The pyriformis is a triangular muscle
covered by the gluteus maximus and the gluteus medius (Fig. 90, _b_) and
overlying the gemellus superior (Fig. 163, 6).

_Origin_ by fleshy fibres from the tips of the transverse processes of
the last two sacral and the first caudal vertebræ. The muscle passes
laterad through the great sciatic notch to its

_Insertion_ by a flat tendon into an elongated area on the proximal
border of the great trochanter just outside (caudad) of the insertion of
the gemellus superior.

_Relations._--Outer surface with the gluteus medius (Fig. 90, _b_) and
the gluteus maximus. Inner surface with the gemellus superior (Fig. 163,
6), the great sciatic nerve (Fig. 163, _a_), and the flexor caudæ longus
(Fig. 68, _x_).

_Action._--Abductor of the thigh.

=M. gemellus superior= (Fig. 163, 6).--The gemellus superior is a
triangular muscle lying beneath the pyriformis (Fig. 163, 7). It is
broader than the pyriformis, so that it projects beyond its borders both
caudad and craniad. It is closely united craniad with the gluteus
minimus, so that the limits of the two are definable only with
difficulty. Its caudal border is closely united to the gemellus
inferior.

_Origin_ by fleshy fibres from an elongated area on the dorsal border of
the ilium and ischium. The area is narrowed craniad. It does not quite
reach the posterior inferior iliac spine in the one direction nor the
spine of the ischium in the other direction. The fibres converge to a
strong tendon the

_Insertion_ of which is into a triangular area dorsad of the tip of the
great trochanter.

_Relations._--Outer surface with the gluteus medius (Fig. 90, _b_), the
pyriformis (Fig. 163, 7), the great sciatic nerve (Fig. 163, _a_), and
the gluteus maximus. Inner surface with the ilium, ischium, the
capsularis, the caudal edge of the gluteus minimus (Fig. 163, 5), and
the cranial edge of the obturator internus (Fig. 90, _e_).

_Action._--Rotates the femur and abducts it so as to carry the foot
outward.

=M. gluteus minimus= (Fig. 163, 5).--The gluteus minimus is a long
triangular muscle beneath the middle of the gluteus medius (Fig. 90,
_b_) and with its caudal border against or covering the cranial border
of the gemellus superior (Fig. 163, 6), to which it is frequently
closely united.

_Origin_ from the ventral half of the ilium, from near its cranial end
to a point midway between the posterior iliac spine and the spine of the
ischium. The muscle ends in a strong flat tendon.

_Insertion_ into an oval facet at the base of the dorsal surface of the
great trochanter on its lateral side.

_Relations._--Outer surface with the gluteus medius (Fig. 90, _b_) and
at the caudal border with the gemellus superior (Fig. 163, 6). Inner
surface with the capsularis and rectus femoris (Fig. 92, _b_).

_Action._--Rotates the femur so as to carry the foot out.

=M. capsularis= (gluteus quartus, or epimeralis).--The capsularis is a
small flat bundle of muscle-fibres which lies obliquely beneath the
gluteus minimus (Fig. 163, 5) and gemellus superior (6) on the lateral
or outer surface of the ilium.

_Origin_ by fleshy fibres from the surface of the ilium over a
triangular area between the origin of the rectus femoris (Fig. 92, _b_)
ventrad, the gemellus superior (Fig. 163, 6) dorsad, and of the gluteus
minimus (Fig. 163, 5) craniad and the acetabulum caudad. The muscle
passes over the smooth surface of the ilium and the pubis ventrad of the
acetabulum and then over the capsule of the joint.

_Insertion_ by fleshy fibres for about one centimeter in the middle line
on the dorsal surface of the femur distad of the great trochanter.

_Relations._--Outer surface with the gluteus minimus (Fig. 163, 5), the
gemellus superior (6), and the vastus lateralis (Fig. 90, _d_). Inner
surface with the ilium, the rectus femoris (Fig. 92, _b_), the capsule
of the joint, and the vastus medialis (Fig. 92, _c_).

_Action._--Rotates the thigh so as to carry the foot inward, hence
antagonizes the iliopsoas.

=M. gemellus inferior.=--The gemellus inferior is a flat triangular
muscle situated just caudad of the gemellus superior and beneath the
obturator internus (Fig. 90, _e_), so that it is seen on reflecting the
latter

_Origin_ from the dorsal one-half of the whole lateral surface of the
ischium between the ischial spine and the ischial tuberosity. The fibres
converge toward its insertion. The inner surface of the muscle is
covered by a strong tendon.

_Insertion_ into the inner surface of the tendon of the obturator
internus (Fig. 90, _e_) by tendon- and muscle-fibres. Some of the
muscle-fibres are inserted into the capsule of the joint.

_Relations._--Outer surface with the obturator internus (Fig. 90, _e_).
Medial surface with the ischium. Caudal border with the quadratus
femoris (Fig. 90, _f_). Cranial border with the gemellus superior.

_Action._--Abductor of the thigh. The muscle may be considered as a
separate head of the obturator internus (Fig. 90, _e_).

=M. quadratus femoris= (Fig. 90, _f_).--The quadratus femoris is a short
thick muscle connecting the ischial tuberosity (2) and the proximal end
of the femur. It lies just caudad of the obturator internus (_e_)
beneath the proximal end of the biceps femoris (Fig. 68, _t_).

The _origin_ is by fleshy fibres from a considerable triangular area on
the lateral surface of the ischium near the tuberosity. The area lies
between the origin areas of the gemellus inferior, biceps,
semimembranosus, and the obturator externus.

_Insertion_ into the distal two-thirds of the ventral border of the
great trochanter and about half the adjacent surface of the lesser
trochanter.

_Relations._--Outer surface with the tenuissimus (Fig. 90, _g_), the
biceps (Fig. 68, _t_), the semitendinosus (Fig. 90, _j_), and the great
sciatic nerve (Fig. 163, _a_). Caudal border with the semimembranosus
(Fig. 90, _i_). Ventral border with the adductor femoris (Fig. 90, _h_);
dorsal border with the obturator internus (Fig. 90, _e_) and gemellus
inferior.

_Action._--Extensor of the thigh and rotator of the femur so as to carry
the foot inward.

=M. obturator externus.=--The obturator externus is a flat triangular
muscle beneath the adductor femoris (Fig. 92, _g_).

_Origin_ by fleshy fibres from the median lip of the obturator foramen
and from both dorsal and ventral surfaces of the rami of the pubis and
ischium adjacent to the lip. Also from the outer surface of the ramus of
the ischium as far as the area for the quadratus femoris (Fig. 90, _f_).
The fibres converge to a strong flat tendon.

  [Illustration: FIG. 90.--MUSCLES ON THE LATERAL SIDE OF THE LEG, AFTER
  REMOVAL OF THE MUSCLES SHOWN IN FIG. 68 (BICEPS, TENSOR FASCIÆ LATÆ,
  CAUDOFEMORALIS, AND GLUTEUS MAXIMUS).

  _a_, M. sartorius; _b_, M. gluteus medius; _c_, M. rectus femoris;
  _d_, M. vastus lateralis; _e_, M. obturator internus; _f_, M.
  quadratus femoris; _g_, M. tenuissimus; _h_, M. adductor femoris; _i_,
  M. semimembranosus; _j_, M. semitendinosus; _k_, M. vastus
  intermedius; _l_, M. plantaris; _m, m′, m″_, M. gastrocnemius, outer
  head (_m_, part from the external sesamoid bone; _m′_, from the
  plantaris; _m″_, from the superficial fascia); _n_, M. tibialis
  anterior; _o_, M. soleus; _p_, M. extensor longus digitorum; _q_, M.
  peroneus longus; _r_, M. peroneus tertius (_r′_, its tendon); _s_, M.
  peroneus brevis; _t_, tendon of Achilles; _u_, M. extensor brevis
  digitorum. 1, great trochanter of femur; 2, tuberosity of ischium,
  with cut origin of M. biceps femoris; 3, patella; 4, calcaneus; 5,
  transverse ligaments; 6, lateral malleolus.]

_Insertion_ into the proximal portion of the bottom of the trochanteric
fossa.

_Relations._--Ventral surface with the adductor femoris (Fig. 92, _g_).
Dorsal surface with the pubis and ischium. Caudal border with the
quadratus femoris (Fig. 90, _f_).

_Action._--Assists the iliopsoas.


B. MUSCLES ON THE MEDIAL SURFACE OF THE HIP.--=M. obturator internus=
(Fig. 90, _e_).--The obturator internus appears as a triangular muscle
caudad of the gemellus superior.

_Origin_ by numerous small separate heads from the dorsal surface of the
ramus of the ischium along its symphysis and following its medial border
from the symphysis nearly to the tuberosity. The fibres form a flat
muscle which narrows and passes through the lesser sciatic notch, turns
ventrad and ends in a strong flat tendon whose

_Insertion_ is into the bottom of the trochanteric fossa of the femur.
The tendon is continued proximad on the inner surface of the muscle and
forms a smooth firm surface by which the muscle glides over the dorsal
border of the ischium. Into the inner surface of this tendon near its
insertion the tendon of the gemellus inferior is inserted.

_Relations._--Medial surface within the pelvis with a mass of fat
separating it from the pelvic organs. Dorsal or outer surface with the
biceps femoris, the tenuissimus, the caudofemoralis, and the great
sciatic nerve. Inner surface with the ischium and the great sciatic
nerve. Caudal (or ventral) border with the quadratus femoris.

_Action._--Abductor of the thigh.

=M. iliopsoas= (Fig. 162, 8; Fig. 91, _c_).--The iliopsoas (equivalent
to the human psoas and iliacus) is a conical muscle emerging from the
abdominal cavity onto the medial surface of the femur.

_Origin._--(_a_) The portion corresponding to the human psoas (Fig. 162,
8) arises by ten vertebral heads. The first five of these come from the
five cranial tendons of origin of the psoas minor (Fig. 162, 9); the
sixth from a tendinous expansion which passes from the tendon of the
first head over the ventral longitudinal muscles to the transverse
process of the fifth lumbar vertebra. The seventh, eighth, ninth, and
tenth heads arise by fleshy fibres from the ventral surfaces of the
centra of the last four lumbar vertebræ.

(_b_) The portion corresponding to the human iliacus arises by fleshy
fibres from the ventral border of the ilium, from opposite the auricular
impression to the iliopectineal eminence. The portions of the muscle all
converge to form a conical mass which ends in a strong tendon lying on
its outer surface.

_Insertion_ by tendon and fleshy fibres into the apex of the lesser
trochanter of the femur.

_Relations._--Dorsal surface with the quadratus lumborum (with which
this muscle is partly united), the rectus femoris (Fig. 91, _d_), and,
by the iliac head, with the gluteus minimus. Ventral and medial surface
with the psoas minor (Fig. 162, 9) and the peritoneum. Lateral edge with
the transversus abdominis (Fig. 162, 4).

_Action_.--Rotates the thigh so as to carry the foot out; also flexes
the thigh.


2. Muscles of the Thigh.

=M. biceps femoris= (Fig. 68, _t_, page 117).--A very large flat muscle
covering about two-thirds of the lateral side of the thigh.

_Origin_ (Fig. 90, 2).--From the ventral surface of the tuberosity of
the ischium by tendon- and muscle-fibres. The fibres diverge, and near
the knee the mass has spread out, ending in a fascia. The dorsal border
of the muscle and the common fascia are continuous dorsad with the
superficial fascia of the thigh and with the tendon of the
caudofemoralis (Fig. 68, _s_). Ventrad it is continuous with the
superficial fascia of the shank.

_Insertion_ into rather more than the proximal one-third of the dorsal
border of the tibia along its lateral margin and into the lateral margin
of the patella. In passing over the knee-joint it is closely united to
the underlying ligaments and tendons.

_Relations._--Outer surface with the superficial fascia and with a few
of the most caudal fibres of the cutaneus maximus (Fig. 62, _b_, page
94). Cranial (or dorsal) edge with the caudofemoralis (Fig. 68, _s_) and
the vastus lateralis (Fig. 90, _d_). Caudal border with the
semitendinosus (Fig. 68, _u_) and a mass of fat. Inner surface with the
caudofemoralis (Fig. 68, _s_), the tenuissimus (Fig. 90, _g_), the
obturator internus (Fig. 90, _e_), the quadratus femoris (Fig. 90, _f_),
the semitendinosus (Fig. 68, _u_), the semimembranosus (Fig. 90, _i_),
the adductor femoris (Fig. 90, _h_), the great sciatic nerve (Fig. 163,
_a_), and distad with the following muscles of the lower leg: the
tibialis anterior (Fig. 90, _n_), the extensor longus digitorum (Fig.
90, _p_), the peroneus longus (Fig. 90, _q_), and the lateral head of
the gastrocnemius (Fig. 90, _m_).

_Action._--Abductor of the thigh, and flexor of the shank.

=M. tenuissimus= or =M. abductor cruris= (Fig. 90, _g_).--A very slender
muscle, only three or four millimeters wide.

_Origin_ from the tip of the transverse process of the second caudal
vertebra, in common with the caudofemoralis (Fig. 68, _s_) or gluteus
maximus. It passes obliquely beneath the biceps femoris (Fig. 68, _t_)
distad and ventrad, to the distal end of the ventral border of that
muscle. Here it becomes continuous with the ventral border of the
biceps, ending in a continuation of the same fascia into which the
biceps is inserted.

_Relations_.--Outer surface with the caudofemoralis (Fig. 68, _s_) and
the biceps femoris (Fig. 68, _t_); distad with the integument. Inner
surface with the obturator internus (Fig. 90, _e_), quadratus femoris
(_f_), semitendinosus (_j_), adductor femoris (_h_), semimembranosus
(_i_), and distad with the muscles of the lower leg.

=M. caudofemoralis= (=parameralis=, Strauss-Durckheim) (Fig. 68, _s_,
page 117).

_Origin_ by a flat tendon from the transverse processes of the second
and third caudal vertebræ. The muscle forms a flat band which passes
distad along the middle of the lateral side of the thigh over the pelvis
and caudad of the great trochanter. At the middle of the thigh it ends
in a very thin tendon. The tendon passes distad along the medial surface
of the biceps femoris (Fig. 68, _t_), pierces the fascia lata near the
knee, and passes to its

_Insertion_ into the middle of the lateral border of the patella.

_Relations._--Outer surface with the superficial fascia and a few fibres
of the cutaneus maximus; distad with the biceps femoris (Fig. 68, _t_).
Cranial border with the gluteus maximus; caudal border with the biceps
femoris. Inner surface with the tenuissimus (Fig. 90, _g_), the gluteus
maximus, the abductor caudæ internus, and with the obturator internus
(Fig. 90, _e_); distad with the vastus lateralis.

_Action._--Abducts the thigh and helps to extend the shank.

=M. semitendinosus= (Fig. 90, _j_).--A long slender muscle on the
ventral (caudal) border of the thigh, between the semimembranosus (_i_)
and the biceps femoris (Fig. 68, _t_).

_Origin_ from the apex of the tuberosity of the ischium beneath the
origin of the biceps femoris. The muscle passes to the medial side of
the shank and ends in a thin but strong tendon (Fig. 92, _i′_) about
five millimeters broad. The tendon curves proximad and passes beneath
the gracilis tendon (Fig. 91, _b_) to its

_Insertion_ into the crest (dorsal border) of the tibia one or two
centimeters from its proximal end.

_Relations._--Lateral surface with the biceps femoris (Fig. 68, _t_),
the integument, a mass of fat, and distad with the gastrocnemius (Fig.
92, _j_) and popliteus (Fig. 92, _k_). Caudal surface with the
integument. Medial surface with the semimembranosus (Fig. 90, _i_) and
distad with the integument of the lower leg.

_Action._--Flexor of the shank.

=M. semimembranosus= (Figs. 90 and 91, _i_; Fig. 92, _h_).--A thick
prismatic muscle lying along the ventral (or caudal) side of the thigh
between the semitendinosus (_j_) and the gracilis (Fig. 91, _b_).

_Origin_ by short tendon-fibres from the caudal border of the tuberosity
and the ramus of the ischium. The muscle mass is divided throughout most
of its length into two portions (Fig. 92, _h_ and _h′_), one of which
(_h′_) lies laterad and caudad of the other. The two portions pass to
the medial side of the knee. The caudal portion (_h′_) ends in a strong
flat tendon five millimeters broad, the

_Insertion_ of which is into the medial surface of the femur on the
medial epicondyle, at the middle of its distal border and into the
adjacent medial surface of the tibia behind the lateral ligament.

The dorsal part has its _insertion_ into the distal one and one-half to
two centimeters of the ridge which is continued from the medial
epicondyle of the femur onto the shaft; and into the sesamoid bone of
the medial epicondyle.

_Relations._--Lateral surface with the semitendinosus (Fig. 90, _j_),
the biceps femoris (Fig. 68, _t_), and distad with a small part of the
adductor femoris (Fig. 92, _g_), and with the gastrocnemius (Fig. 92,
_j_). Medial surface with the gracilis (Fig. 91, _b_) and distad with
the sartorius (Fig. 91, _a_). Cranial (or dorsal) border at the origin
with the quadratus femoris (Fig. 90, _f_); for the remainder of its
length with the adductor femoris (Fig. 90, _h_). Caudal border with the
integument proximad.

_Action._--Extensor of the thigh.

  [Illustration: FIG. 91.--MUSCLES ON THE MEDIAL SIDE OF THE LEG.

  _a_, M. sartorius; _b_, M. gracilis; _c_, M. iliopsoas; _d_, M. rectus
  femoris; _e_, M. vastus medialis; _f_, M. pectineus; _g_, M. adductor
  longus; _h_, M. adductor femoris; _i_, M. semimembranosus; _j_, M.
  semitendinosus; _k_, medial head of M. gastrocnemius; _l_, M.
  plantaris; _m_, M. flexor longus hallucis (_m′_, its tendon); _n_, M.
  flexor longus digitorum; (_n′_, its tendon); _o_, M. tibialis
  posterior; _p_, M. tibialis anterior; _q_, M. interosseus of second
  digit. 1, patella; 2, calcaneus; 3, medial malleolus; 4, second
  metatarsal; 5, transverse ligament of the lower leg.]

=M. sartorius= (Fig. 91, _a_; Fig. 68, _q_).--A large flat muscle along
the medial side of the thigh near its cranial (dorsal) border.

_Origin_ from the ventral half of the crest of the ilium and from the
medial half of its ventral border craniad of the auricular impression.
The caudal third of the origin is by a thin tendon, the rest by fleshy
fibres.

_Insertion_ on a long S-shaped line which begins on the dorsal border of
the tibial shaft about two centimeters from its proximal end, passes
thence to the middle of the proximal end of the medial surface of the
tibia, thence across the ligaments of the knee-joint and the medial
surface of the medial epicondyle to the patella, crosses the patella
obliquely to the middle of its proximal end, and may be continued for
some distance proximad along the middle line on the fascia.

_Relations._--Medial surface with the integument and proximad with the
internal oblique muscle (Fig. 68, _p_). Lateral (inner) surface with the
tensor fasciæ latæ (Fig. 68, _r_), the vastus lateralis (Fig. 90, _d_),
the superficial fascia, the vastus medialis (Fig. 92, _c_), the rectus
femoris (Fig. 92, _b_), and the distal end of the semimembranosus (Fig.
92, _h′_).

_Action._--Adducts and rotates the femur and extends the tibia.

=M. gracilis= (Fig. 91, _b_).--The gracilis is a flat, thin,
subcutaneous muscle occupying the ventral half of the medial surface of
the thigh.

_Origin_ by a strong tendon from the caudal three-fourths of the
symphysis of the ischium and pubis. The tendon may extend caudad of the
symphysis in the middle line to the level of the tuberosity of the
ischium. For about its first centimeter the tendon is common to the two
muscles of opposite sides and gives origin on two sides to the fibres of
the adductor femoris. The common tendon divides into two which pass
laterad, each ending in a convex border from which the muscle-fibres
spring.

_Insertion._--It ends in a thin aponeurosis, part of which is continuous
with that of the sartorius. The aponeurosis is finally inserted into the
medial surface of the tibia near its proximal end, while distally it is
continuous with the fascia.

_Relations._--Outer (medial) surface with the integument. Inner
(lateral) surface with the semimembranosus (Fig. 91, _i_) and the
adductor femoris (Fig. 91, _h_).

_Action._--Adducts the leg and draws it caudad.

=M. adductor femoris= (magnus et brevis) (Fig. 92, _g_; Fig. 90,
_h_).--The adductor femoris lies between the semimembranosus (Fig. 92,
_h_) and the femur. Its proximal part is covered by the semimembranosus,
while its distal part lies outside of it.

_Origin_ by muscle-fibres from the rami of the pubis and the ischium
along the whole of the length of the symphysis; from the ramus of the
ischium between the symphysis and the tuberosity, and from the tendon of
origin common to the two gracilis muscles.

_Insertion_ into nearly the whole of the ventral surface of the shaft of
the femur. The area begins at the base of the great trochanter opposite
the proximal end and the insertion area of the gluteus maximus. It
extends thence distad along the caudal border of the surface as an area
about one millimeter wide. At the junction of the first and second
thirds of the shaft the area expands and occupies the whole of the
ventral surface of the bone, ending at the intercondyloid fossa.

_Relations._--Lateral surface with the biceps (Fig. 68, _t_), the great
sciatic nerve (Fig. 163, _a_), the tenuissimus (Fig. 90, _g_), and the
semimembranosus (Fig. 92, _h_); dorsolateral border in contact with the
vastus lateralis (Fig. 92, _c_). Dorsal surface with the quadratus
femoris (Fig. 90, _f_) and obturator externus (Fig. 90, _e_). Caudal
surface with the semimembranosus (Fig. 92, _h_). Medial surface with the
gracilis (Fig. 91, _b_), adductor longus (Fig. 92, _f_), pectineus (Fig.
92, _e_), vastus medialis (Fig. 92, _c_), and distad with the medial
head of the gastrocnemius (Fig. 92, _j_).

_Action._--An extensor of the thigh.

=M. adductor longus= (Fig. 91, _g_; Fig. 92, _f_).--A thin muscle which
covers the dorsal half of the medial surface of the adductor femoris
(Fig. 92, _g_).

_Origin_ by muscle-fibres from the median three-fourths of the cranial
border of the pubis, the line of origin forming a medial continuation of
that of the pectineus (Fig. 92, _e_).

_Insertion_ by a thin aponeurosis into the external linea aspera of the
femur along the second and third fifths of the bone.

_Relations._--With its medial or cranial surface the adductor longus
forms part of the boundary of a depression among the muscles at the
proximal end of the medial side of the leg. This depression is called
the iliopectineal fossa; it contains the femoral vein and artery and
saphenous nerve imbedded in fat (Fig. 127). The medial edge of the
adductor longus is in relation with the integument; the lateral edge
with the pectineus (Fig. 92, _e_). Inner or caudal surface with the
adductor femoris (Fig. 92, _g_).

_Action._--Adductor of the thigh.

  [Illustration: FIG. 92.--SECOND LAYER OF MUSCLES ON THE MEDIAL SIDE OF
  THE THIGH.

  _a_, M. tensor fasciæ latæ; _a′_, fascia lata; _b_, M. rectus femoris;
  _c_, M. vastus medialis; _d_, M. iliopsoas (cut); _e_, M. pectineus;
  _f_, M. adductor longus; _g_, M. adductor femoris; _h_, _h′_, M.
  semimembranosus; _i_, M. semitendinosus (_i′_, its tendon); _j_,
  medial head of M. gastrocnemius; _k_, M. popliteus; _l_, M. flexor
  longus digitorum. 1, patellar ligament; 2, ligamentum collaterale
  tibiale.]

=M. pectineus= (Fig. 92, _e_).--A flat band of fibres closely united
with the adductor longus (_f_), of which it appears to be a lateral
continuation.

_Origin_ by fleshy fibres from the lateral one-fourth of the cranial
border of the pubis. The muscle passes over the smooth outer surface of
the pubis between its origin area and the acetabulum, crosses the
iliopsoas (_d_) obliquely and has its

_Insertion_ by muscle-fibres into an elongated area (five millimeters in
length) on the shaft of the femur just distad of the lesser trochanter
and between the insertion of the adductor femoris (_g_) and that of the
vastus medialis (_c_).

_Relations._--The cranial edge forms part of the floor of the
iliopectineal fossa. Lateral surface in relation with the iliopsoas
(_d_) and vastus medialis (_c_); medial surface with the adductor longus
(_f_) and adductor femoris (_g_).

_Action._--Adductor of the thigh.

=M. quadriceps femoris.=--The quadriceps femoris is a very powerful
extensor muscle on the front of the thigh. It consists of four muscles
which unite to form the great extensor of the shank. It is inserted into
the patella and through it, by the ligamentum patellæ, into the tibia.
It may be compared to the triceps brachii. The parts are:

(1) =M. rectus femoris= (Fig. 92, _b_; Fig. 90, _c_).

_Origin_ by strong tendon from an elongated triangular area which has
its base at the acetabulum and its apex about five to seven millimeters
craniad of the acetabulum, along the ventral border of the ilium. The
area is between that for the capsularis and that for the iliopsoas. The
muscle is flat near its origin, but soon becomes a triangular prismatic
mass which is united to the dorsal border of the vastus lateralis (Fig.
90, _d_) at the junction of the middle and last thirds of the thigh.

_Insertion_ into the oblique area on the outer surface of the patella
near its proximal border in connection with the vastus lateralis.

_Relations._--Outer or lateral surface at the origin with the gluteus
minimus, the edge of the capsularis, the gluteus medius (Fig. 90, _b_),
and farther distad with the vastus lateralis (Fig. 90, _d_). Medial
surface with the tensor fasciæ latæ (Fig. 92, _a_), sartorius (Fig. 90,
_a_), and vastus medialis (Fig. 92, _c_). Inner (caudal) surface with
the vastus intermedius.

(2) =M. vastus lateralis= (Fig. 90, _d_).--A flat triangular prismatic
mass joined distally to the preceding. It covers the dorsal part of the
lateral surface of the thigh.

_Origin_ from a triangular area on the dorsal and lateral surfaces of
the shaft and the great trochanter of the femur. The base of the area is
at the great trochanter, and its apex is at the junction of the second
and third fifths of the shaft on the linea aspera. The linea aspera
forms the ventral boundary of the triangle, while its dorsal boundary is
formed by a line drawn from its apex to the dorsomedial angle of the
great trochanter. The mass unites with the rectus femoris (_c_) by its
dorsal border at the junction of the middle and distal thirds of the
thigh.

_Insertion_ into the oblique area on the outer surface of the patella
near its lateral border in connection with the rectus femoris.

(3) =M. vastus medialis= (Fig. 92, _c_) lies on the medial side of the
thigh.

_Origin_ by fleshy fibres over a diamond-shaped area on the shaft of the
femur lying between the medial branch of the linea aspera and the area
for the vastus lateralis. Proximad the area is bounded by the spiral
line, and distad it is bounded by a line parallel to the spiral line and
having its proximal end at about the junction of the first and second
thirds of the bone. The muscle forms a triangular, prismatic mass. It
ends in a thin aponeurosis which is continuous dorsad with the border of
the rectus femoris (Fig. 92, _b_), and ventrad sometimes with the tendon
of the gracilis (Fig. 91, _b_).

_Insertion_ into the medial border of the patella and the ligamentum
patellæ. The insertion may extend onto the head of the tibia.

The adjacent surfaces of the vastus lateralis and the vastus medialis
are connected over their distal thirds by an aponeurosis which passes
transversely beneath the rectus femoris. The distal end of the
aponeurosis is inserted into the proximal border of the patella. Its
proximal end receives the insertion of some muscle-fibres which form a
part of the vastus medialis as here described. This mass of fibres is
described by Strauss-Durckheim as the =crural= muscle. Sometimes the
transverse aponeurosis is continuous with only one of the two vasti and
sometimes with neither, so that the insertion of the crural of
Strauss-Durckheim becomes more or less independent.

_Relations_ of the vastus medialis.--Outer (medial) surface with the
sartorius (Fig. 91, _a_) and the structures in the iliopectineal fossa.
Cranial (or dorsal) surface with the rectus femoris (Fig. 92, _b_) and
vastus intermedius. Caudal (ventral) surface with the pectineus (Fig.
92, _e_), adductor longus (Fig. 92, _f_), adductor femoris (Fig. 92,
_g_), and semimembranosus (Fig. 92, _h_).

(4) =M. vastus intermedius.=--A flat mass of muscle which lies beneath
the rectus femoris.

_Origin_ from nearly the whole of the dorsal surface of the shaft of the
femur between the areas for the vastus medialis and vastus lateralis.
The area of origin extends distad to an oblique line the middle of which
is about one and one-half centimeters from the patellar surface, the
lateral border of the area being longer than the medial border.

_Insertion_ by muscle-fibres into the capsule of the joint. The central
fibres are inserted about one centimeter proximad of the patella, while
the lateral mass passes to the level of the proximal end.

_Relations._--Outer surface with the rectus femoris (Fig. 92, _b_);
borders with the vastus medialis (Fig. 92, _c_) and vastus lateralis
(Fig. 90, _d_); inner surface with the femur.

_Action._--The quadriceps extensor is an extensor of the shank. The
vastus intermedius acting separately is a tensor of the capsule of the
knee-joint.


3. Muscles of the Lower Leg (Crus).


A. ON THE VENTRAL SIDE.--=M. gastrocnemius.=--This is the great muscular
mass of the calf. It arises by two heads, the caput laterale or lateral
head (Fig. 90, _m_), and the caput mediale or medial head (Fig. 91,
_k_), of the gastrocnemius.

=Caput laterale= (Fig. 90, _m_, _m′_, _m″_).--The origin of the lateral
head is in four portions:

(1) From the tendon of origin of the plantaris which comes from the
middle of the lateral border of the patella. The tendon ends in a small
conical mass of fibres (_m′_) which joins the ventral part of the common
head.

(2) By a slender flat tendon, distad of the first, from the superficial
fascia of the shank (_m″_). The tendon ends in a conical mass which
joins the dorsal border of the common head.

(3) By a strong tendon and by muscle-fibres from the distal border of
the lateral sesamoid bone (Fig. 61, 3) of the femur. These fibres (_m_)
form the middle and outer part of the common head.

(4) By muscle-fibres from the middle of the outer surface of the
aponeurosis covering the plantaris (Fig. 90, _l_) along rather more than
the proximal half of the tibia. The lateral head thus formed is flat and
fusiform in section.

=Caput mediale= (Fig. 91, _k_; Fig. 92, _j_).--The medial head resembles
the lateral head closely.

_Origin_ by a strong tendon from the medial sesamoid bone of the femur
(Fig. 61, 4) and by muscle-fibres from the surface of the shaft for a
short distance proximad of this.

The two heads unite by their contiguous borders at the junction of the
first and second thirds of the tibia. The common muscle narrows rapidly
and ends in a flat tendon which joins the tendon of the soleus to form
the so-called tendon of Achilles (tendo calcaneus) (Fig. 90, _t_). This
has its

_Insertion_ into the proximal end of the calcaneus (Fig. 90, 4) near its
ventral border. This tendon together with that of the soleus (Fig. 90,
_o_) and the fascia of the shank forms a tubular sheath for the tendon
of the plantaris.

_Relations._--(1) Of the lateral head. Lateral (outer) surface with the
biceps femoris (Fig. 68, _t_) and the superficial fascia. Medial (inner)
surface with the popliteus (Fig. 92, _k_), the plantaris (Fig. 90, _l_)
(to which it is closely united), the medial head of the gastrocnemius
(Fig. 91, _k_), the soleus (Fig. 90, _o_), and the peroneus longus (Fig.
90, _q_). (2) Of the medial head. Medial (outer) surface with the
superficial fascia and the tendons of the gracilis (Fig. 91, _b_),
semimembranosus (Fig. 92, _h′_), and semitendinosus (Fig. 92, _i_).
Lateral (inner) surface at the origin with the adductor femoris (Fig.
92, _g_), then with the plantaris (Fig. 91, _l_), the popliteus (Fig.
92, _k_), flexor longus digitorum (Fig. 91, _n_), and the lateral head
of the gastrocnemius (Fig. 90, _m_).

_Action._--Extensor of the foot. (It is to be noted that what is called
=extension= in the foot is analogous to what is called =flexion= in the
hand, so that the extensors of the foot are most readily to be compared
with the flexors of the hand.)

=M. plantaris= (Fig. 90, _l_; Fig. 91, _l_).--A fusiform muscle covered
distally by the gastrocnemius, but appearing between the two heads of
the gastrocnemius at their proximal ends (Fig. 90, _l_).

_Origin_ by a strong tendon from the middle of the lateral border of the
patella and by fleshy fibres from the ventral border of the lateral
sesamoid.

The patellar tendon ends in a flattened head which passes ventrad over
the lateral epicondyle of the femur and then curves distad; it is
closely united with the lateral head of the gastrocnemius. The muscle
ends in a thick tendon which passes through a sheath formed by the
tendons of the gastrocnemius and soleus, and the fascia of the shank.
The tendon passes over the grooved proximal end of the calcaneus onto
its ventral surface. It is held in place against the groove by two
sheets of aponeurosis, which leave the tendon on either side for a
distance of more than a centimeter and are attached to the lateral
surfaces of the calcaneus at its proximal end. Lateral motion is thus
hindered, while longitudinal motion is permitted.

Between this tendon and the tendon of Achilles is a synovial bursa which
aids the gliding movement of the tendon. In the sole of the foot
opposite the distal end of the calcaneus the tendon broadens and ends in
the flexor brevis digitorum (pedis perforatus) muscle, which might also
be considered as a second part of the plantaris. In man the plantaris is
inserted into the calcaneus along with the gastrocnemius.

_Relations._--The muscle is covered throughout by the two heads of the
gastrocnemius (Fig. 90, _m_; Fig. 91, _k_), except at the proximal end
(Fig. 90, _l_), where it is in contact with the integument. Inner
surface in relation with the popliteus (Fig. 92, _k_), the soleus (Fig.
90, _o_), the flexor longus digitorum (Fig. 91, _n_), and flexor longus
hallucis (Fig. 91, _m_).

=M. soleus= (Fig. 90, _o_).--A flat fusiform muscle lying beneath the
plantaris.

_Origin_ by muscle-fibres from the lateral surface of the head of the
fibula, and by tendon-fibres from the proximal two-fifths of its ventral
border.

_Insertion._--The muscle ends in a slender tendon which joins the
lateral border of the gastrocnemius tendon to form the tendon of
Achilles (Fig. 90, _t_), which forms the sheath of the plantaris tendon.

_Relations._--Outer surface with the gastrocnemius (Fig. 90, _m_) and
plantaris (Fig. 90, _l_). Inner surface with the peroneus longus (Fig.
90, _q_), peroneus tertius (Fig. 90, _r_), and flexor hallucis (Fig. 91,
_m_).

_Action._--Assists the gastrocnemius to extend the foot.

=M. triceps suræ.=--The gastrocnemius and the soleus are sometimes
considered as forming a single muscle, with three heads, under the name
triceps suræ.

=M. popliteus= (Fig. 92, _k_).--A triangular muscle passing from the
femur obliquely toward the medial side over the ventral surface of the
proximal end of the tibia.

_Origin_ by a strong tendon from the popliteal groove on the surface of
the lateral epicondyle of the femur. In the tendon is a sesamoid bone,
the popliteal bone (Fig. 61, 5, page 89), which glides over the ventral
part of the lateral articular facet on the proximal end of the tibia. As
the muscle passes over the joint it is closely attached to the joint
capsule. From the popliteal bone, which with the tendon lies within the
capsule of the knee-joint, the muscle-fibres diverge to their

_Insertion_ into the proximal end of the ventral surface of the tibial
shaft on the medial side of the medial oblique ridge. The area of
insertion extends slightly onto the medial surface of the bone.

_Relations._--Outer surface with the gastrocnemius (Fig. 92, _j_) and
plantaris (Fig. 91, _l_), and with the tendon of the semitendinosus
(Fig. 92, _i_). Distal border with the origins of the soleus and flexor
longus digitorum. Inner surface with the capsule of the knee-joint and
the tibia.

_Action._--Rotates the thigh so as to turn the toes inward.

       *       *       *       *       *

The three following deep muscles on the ventral surface of the shank are
covered by a deep fascia (the deep crural fascia) which separates them
from the overlying muscles. This fascia stretches from the dorsal border
of the tibia about the ventral side of the shank to the medial border of
the tibia. It sends a slip beneath the border of the fibula.

=M. flexor longus digitorum= (Fig. 91, _m_ and _n_).--Owing to the
reduction of the first digit in the cat the tendon of the flexor longus
hallucis (_m_) has become united to that of the flexor longus digitorum
(_n_), so that the two might be considered separate heads of a single
muscle. The head corresponding to the flexor longus hallucis (_m_) is
much larger than that corresponding to the flexor longus digitorum
(_n_). The two heads will be described separately.

(1) =M. flexor longus hallucis= (Fig. 91, _m_).--This lies against the
ventral surface of the tibia and fibula beneath the popliteus (Fig. 92,
_k_) and soleus (Fig. 90, _o_).

_Origin_ by fleshy fibres, (1) from the sheet of deep crural fascia
which dips between it and the tibialis posterior (Fig. 91, _o_) and the
flexor longus digitorum (_n_). (2) From the ventral surface of the tibia
distad of the lateral oblique line to within one to three centimeters of
the distal end of the shaft. (3) From the medial surface of the shaft
and head of the fibula and from the whole interosseous ligament. On the
fibular side the origin may extend onto the tendon of the popliteus and
the fascia of the peroneus longus. The fibres form a flat fusiform mass
ending one centimeter from the heel in a strong flat tendon (_m′_) which
passes over the groove on the distal surface of the astragalus and over
the groove on the sustentaculum tali. The two grooves are converted into
a continuous canal by strong transverse ligaments, and the canal is
lined by an extension of the synovial bursa of the ankle-joint. Emerging
from the canal the tendon broadens and receives on its medial side the
insertion of the tendon of the flexor longus digitorum (_n_). The tendon
gives origin on its outer surface to the lumbricales and to the common
plantar ligament. The tendon continues to broaden until it reaches the
middle of the length of the metacarpals; here it divides into four
tendons which pass to the terminal phalanges of the digits.

_Insertion._--The relations of the four tendons and their insertions are
identical with those of the flexor profundus digitorum of the hand.

_Relations._--Outer surface with the soleus (Fig. 90, _o_) and plantaris
(Fig. 91, _l_). Lateral border with the soleus, the peroneus tertius
(Fig. 90, _r_), and peroneus brevis (Fig. 90, _s_). Medial border with
the tibialis posterior (Fig. 91, _o_) and flexor longus digitorum (Fig.
91, _n_).

_Action._--Flexor of the phalanges.

(2) =M. flexor longus digitorum= (Fig. 91, _n_).

_Origin_ by muscle- and tendon-fibres from the ventral surface of the
tibia over its proximal half between the oblique ridges; by fleshy
fibres from an aponeurosis between it and the tibialis posterior (Fig.
91, _o_), and by tendon from the medial surface of the head of the
fibula. At the junction of the middle and distal thirds of the bone the
muscle ends in a slender tendon which passes through the ventral groove
on the medial surface of the tibia and, curving onto the sole of the
foot, becomes attached to the medial border of the common tendon
described under the last.

_Relations._--Outer surface with the medial head of the gastrocnemius
(Fig. 91, _k_) and with the superficial fascia. Inner surface with the
tibialis posterior (Fig. 91, _o_). Medial border at the proximal end
with the popliteus (Fig. 92, _k_), lateral border with the tibialis
posterior (Fig. 91, _o_), and flexor longus hallucis (Fig. 91, _m_).

_Action._--Flexor of the phalanges.

=M. tibialis posterior= (Fig. 91, _o_).--A slender flat fusiform muscle
beneath the flexor longus digitorum and between it and the flexor longus
hallucis.

_Origin_ by fleshy fibres from nearly the whole medial surface of the
head of the fibula, from the inner surface of the aponeurosis between it
and the flexor longus digitorum (_n_), and by a few fleshy fibres from
the ventral surface of the tibia between the oblique ridges. Some fibres
may also arise from the outer surface of the aponeurosis covering the
flexor longus hallucis (_m_). The muscle ends at about the middle of the
tibia in a slender flat tendon which passes parallel to the tendon of
the flexor longus digitorum (_n_) through the dorsal groove on the
medial surface of the distal end of the tibia. This groove is converted
into a canal by a transverse ligament. Beyond the canal the tendon turns
onto the plantar surface of the foot and passes through a groove on the
ventral surface of the scaphoid bone. It then divides.

_Insertion_ into the outer tuberosity on the surface of the scaphoid,
and onto the proximal end of the ventral surface of the medial
cuneiform.

_Relations._--Outer and medial surface with the flexor longus digitorum
(_n_). Lateral surface with the flexor longus hallucis (_m_).

_Action._--Extensor of the foot.


B. MUSCLES ON THE DORSAL AND LATERAL SURFACES OF THE LOWER LEG.--=M.
peroneus longus= (Fig. 90, _q_).--A slender, fusiform muscle lying
superficially on the lateral side of the leg, dorsad of the soleus.

_Origin_ by tendon-fibres from the lateral surface of the head of the
fibula and from the proximal half of the lateral surface of its shaft.

At the junction of the middle and distal thirds of the lower leg the
muscle ends in a slender tendon which passes through the groove on the
lateral surface of the lateral malleolus. This groove is converted into
a canal by a transverse ligament. The tendon passes through the groove
on the peroneal tubercle of the calcaneus, then turns onto the sole of
the foot and passes through the peroneal groove on the cuboid bone. It
then turns mediad and passes through the groove between the ventral
processes of the lateral cuneiform and the metatarsal until it reaches
the first metatarsal. The entire groove is converted into a canal by the
overlying ligaments.

_Insertion_ into (1) the base of the fifth metatarsal, and (2) the outer
side of the base of the first metatarsal, and (3) by slender branches
into the bases of the other metatarsals.

_Relations._--Outer (lateral) surface with the superficial fascia and
the tendon of the biceps femoris. Inner surface with the peroneus
tertius (_r_) and peroneus brevis (_s_), and with the extensor longus
digitorum (_p_). At the proximal end the dorsal border touches the
tibialis anterior (_n_).

_Action._--Flexor of the foot.

=M. peroneus tertius= (Fig. 90, _r_).--A slender fusiform muscle beneath
the peroneus longus (_q_).

_Origin_ by fleshy fibres from about the second quarter of the lateral
surface of the fibula. The muscle ends in a slender tendon (_r′_), which
passes with that of the peroneus brevis (_s_) through the groove on the
ventral border of the lateral malleolus. The groove is converted into a
canal by a transverse ligament. Emerging from it, the tendon turns and
passes along the outer margin of the foot. In passing the sesamoid at
the base of the first phalanx of the fifth digit it is united to it by a
band which passes from the sesamoid to the tendon.

The _insertion_ is finally into the lateral border of the extensor
tendon of the fifth digit as it passes from the first to the second
phalanx.

_Relations._--Outer surface with the peroneus longus (_q_), the soleus
(_o_), and the superficial fascia. Ventral border with the soleus (_o_)
and flexor longus hallucis (Fig. 91, _m_). Inner surface with the
peroneus brevis (Fig. 90, _s_).

_Action._--Extensor and abductor of the fifth digit and flexor of the
foot.

=M. peroneus brevis= (Fig. 90, _s_) lies beneath the other peronei.

_Origin_ by fleshy fibres from the distal half of the surface of the
fibula, which it embraces. At the lateral malleolus the muscle ends in a
thick tendon which passes through the canal on the ventral surface of
the malleolus. In the canal it is enlarged and surrounded by a synovial
bursa. It then turns onto the foot and passes over the dorsal surface of
the calcaneus on its lateral side and has its

_Insertion_ into the tubercle on the lateral side of the base of the
fifth metatarsal.

_Relations._--Outer surface with the peronei longus (_q_) and tertius
(_r_). Inner surface with the bone.

_Action._--Extensor of the foot.

=M. extensor digitorum longus= (Fig. 90, _p_).--A fusiform muscle which
lies beneath the tibialis anterior (_n_), against the interosseous
membrane, and between the tibialis anterior and the peronei.

_Origin_ by a thin flat tendon from the lateral surface of the lateral
epicondyle of the femur just dorsad of the origin of the popliteus. The
tendon becomes narrower and thicker and passes through the capsule of
the knee-joint and over a slight groove on the tibia just dorsad of the
head of the fibula. The belly of the muscle extends the entire length of
the tibia, passing beneath the transverse ligament (5) along with the
tendon of the tibialis anterior (_n_). At the ankle it runs through a
fibrous loop which is attached to the dorsal surface of the calcaneus
(the annular ligament of the calcaneus); it then turns and passes onto
the dorsum of the foot. The muscle ends in four slender tendons, the two
middle of which begin at the transverse ligament, while the others begin
at the fibrous loop. The tendons diverge to the four digits. Each tendon
is connected with the fibrous sheath surrounding the base of the first
phalanx, and each has a synovial bursa beneath it at this point. Near
the distal end of the first phalanx the tendon is united on the lateral
side to the conjoined tendon of the extensor brevis digitorum and an
interosseus muscle, and on the medial side to the tendon of the
interosseus. The lateral side of the most lateral tendon is not thus
united, but is joined on the outer side by the tendon of the peroneus
tertius.

_Insertion._--The tendon thus formed on the dorsum of each phalanx by
the junction of the two or three tendons above mentioned is firmly
attached to the base of the second phalanx at its proximal end in the
middle of its dorsal surface. In crossing the joint between the first
and second phalanges the tendon forms a fibrous pad which protects the
dorsum of the joint and glides over it. It then continues to be inserted
into the base of the terminal phalanx.

_Relations._--Outer surface with the tibialis anterior (_n_) and the
superficial fascia. Inner surface with a part of the tibialis
anterior, with the bones, the interosseous membrane, and the peroneus
brevis (_s_).

_Action._--Extensor of the phalanges.

=M. tibialis anterior= (Fig. 90, _n_).--This is the superficial muscle
covering the lateral side of the tibia.

_Origin_ by fleshy fibres from the proximal one-sixth of the lateral
surface of the shaft of the tibia, from the proximal third of the medial
border of the shaft and head of the fibula, and from the intervening
interosseous ligament. The triangular body of the muscle covers the
lateral surface of the tibia and the outer surface of the extensor
longus digitorum (_p_). Near the malleolus it ends in a strong tendon
which passes beneath the transverse ligament along with the tendon of
the extensor longus (_p_). The tendon crosses the dorsal surface of the
foot obliquely toward its medial side.

_Insertion_ into the outer surface of the first metatarsal.

_Relations._--Outer surface with the superficial fascia and the tendon
of the biceps femoris. Inner surface with the extensor longus (_p_), the
tibia, and the interosseous membrane.

_Action._--Flexor of the foot.


4. Muscles of the Foot.


A. MUSCLES ON THE DORSUM OF THE FOOT.--=M. extensor brevis digitorum=
(Fig. 90, _u_).--A broad thin muscle covering the tarsus and part of the
metatarsus on the lateral side of the dorsum of the foot. It may be
divided into three slips.

_Origin_ from the distal border of nearly the whole calcaneal annular
ligament (5), and from the proximal end of the dorsal surface of the
three lateral metatarsals. At the middle of the metatarsals the muscle
ends in three flat tendons which pass into the three interspaces between
the four tendons of the extensor longus. Each tendon is divided into two
branches.

_Insertion._--The lateral branch of each tendon is inserted into the
cartilaginous plate which lies in the metatarsophalangeal articulation
of the digit on the outer side. The medial branch joins the lateral side
of the extensor longus tendon on the dorsum of the first phalanx.

_Action._--Extensor of the digits.


B. MUSCLES OF THE SOLE OF THE FOOT.--=M. flexor brevis digitorum=
(=pedis perforatus=).--This is the direct continuation of the tendon of
the plantaris. It lies immediately beneath the superficial plantar
fascia. The flat belly of the muscle has its medial border attached by
an oblique tendinous band to the medial surface of the scaphoid and the
medial cuneiform. It divides into four slips which diverge to the four
toes, each ending in a flat tendon. The slips decrease in size from the
lateral to the medial side. The three lateral ones overlap one another
proximally.

_Insertion._--Each tendon expands at the distal end of the metatarsal
and is wrapped about the tendon of the deep flexor which perforates it.
The two halves unite beneath the perforating tendon and pass together
with the perforating tendon through fibrous rings, the annular
ligaments. One of these is attached to the sesamoids at the base of the
phalanx. The other is attached to the head of the first phalanx. The
tendons are finally inserted into the bases of the second phalanges.

The two annular ligaments are connected by fascia so as to form a
continuous canal for the tendons. This canal is lined by a synovial
membrane. Covering this canal is a more superficial layer of fascia.
Before passing into the proximal annular ligament the two middle tendons
unite each with the tendon of the corresponding lumbrical muscle. Each
also gives off a branch, the lateral one on its lateral side and the
medial one on its medial side. These branches, like those of the two
middle ones, are inserted into the common phalangeal fascia.

_Action._--Flexor of the second phalanges of the digits.

=M. quadratus plantæ= (called also the plantar head of the flexor longus
digitorum) is a thin flat muscle which takes _origin_ from the dorsal
part of the lateral surface of the calcaneus and the cuboid. Its fibres
converge to a flat tendon which passes transversely across the flexor
longus digitorum and beneath the flexor brevis digitorum and
calcaneometatarsal.

_Insertion._--Into the medial part of the outer surface of the tendon of
the flexor longus digitorum.

_Action._--It holds the flexor longus tendon in place.

=Mm. lumbricales.=--These are six.

_Origin._--The three larger ones have origin from the outer surface of
the expanded portion of the flexor longus digitorum on its distal half.
Each ends in a slender tendon.

_Insertions._--The tendons unite with the divisions of the tendon of the
flexor brevis which pass to the three lateral digits, at their entrance
to the first annular ligament. The one to the fifth digit is sometimes
absent.

The other three have _origin_ from the tendon of the flexor longus
digitorum at the point where it divides. Each occupies one of the three
intervals between the four divisions, and its fibres originate from the
proximal ends of the two tendons which bound its interval.

_Insertion_ by a very slender tendon into the medial side of the first
phalanges of the third, fourth, and fifth digits near their bases.

_Action._--Move the third, fourth, and fifth digits toward the medial
side.

=Mm. interossei.=--The interosseus of the second digit forms five
portions, which cover the ventral surface of the digit.

_Origin._--(1) By two tendons from the ventral process of the lateral
cuneiform. The muscle divides into four parts, three of which pass to
the medial side of the digit and act as abductors. They are called the
long, short, and middle abductors (abductor longus, brevis, and
intermedius digiti secundi).

_Insertions._--The short head into the medial sesamoid of the
metatarsophalangeal joint, the middle into the medial side of the base
of the first phalanx, and the long into the extensor communis tendon
near the distal end of the first phalanx. The names long, short, and
middle refer to the lengths of the tendons as determined by their points
of insertion.

The _fourth_ portion which comes from the lateral cuneiform has its
_insertion_ into the lateral side of the extensor tendon near the distal
end of the first phalanx. It is therefore an adductor longus digiti
secundi. In some cases there is an adductor brevis from this same head.

(2) The fifth part of the interosseus of the second digit has _origin_
from the middle of the ligament covering the peroneal canal, along with
the middle adductor of the fifth digit. The two muscles diverge.
_Insertion_ into the outer side of the base of the first phalanx of the
second digit. It is an adductor medius digiti secundi.

The interossei of the third and fourth digits are alike.

_Origin_ from the ventral surface of the base of the metatarsal. The
muscles cover the ventral surface of the shaft. At the head each divides
and passes onto the sides of the metatarsal.

_Insertion._--Each half of the muscle shows a tendency to divide into
two parts. One of these, the more superficial and ventral, ends in a
tendon which joins the extensor tendon near the distal end of the first
phalanx. The other part is inserted by short tendon- and muscle-fibres
into the side of the base of the first phalanx; one of the parts is
therefore a middle, and the other a long, adductor or abductor, the
adductores and abductores digiti tertii and quarti.

The fifth digit has five short muscles.

=M. abductor medius digiti quinti.=

_Origin_ from the ventral surface of the calcaneus and from the fifth
metatarsal.

_Insertion_ by a slender tendon into the lateral side of the base of the
first phalanx of the fifth digit.

=M. adductor medius digiti quinti.=

_Origin_ with the adductor medius digiti secundi.

_Insertion_ on the inner side of the base of the phalanx of the fifth
digit.

=M. opponens digiti quinti.=

_Origin_ by a flat tendon from the middle of the ligament which covers
the peroneal canal. It passes obliquely outward parallel to the last.

_Insertion_ on the inner side of the shaft of the fifth metatarsal.

The two remaining muscles of the fifth digit take _origin_ from the
outer part of the ligament covering the peroneal canal. They cover the
ventral surface of the shaft.

_Insertion._--The lateral one is inserted into the lateral sesamoid and
is therefore an abductor brevis. The medial one is inserted into the
extensor tendon and is therefore an adductor longus.


C. MUSCLES OF THE TARSUS.--=M. calcaneometatarsalis= (part of M.
adductor minimi digiti?).--A weak muscle made up largely of
tendon-fibres, some of which pass directly from origin to insertion. It
may be regarded as a ligament.

_Origin_, the lateral and ventral surface of the calcaneus near the
proximal end. It passes distad and slightly laterad outside of the
quadratus plantæ.

_Insertion_, the lateral side of the base of the fifth metatarsal, and
the adjacent surfaces of the cuboid and calcaneus.

_Action._--Probably causes slight motion of the cuboid on the head of
the calcaneus.

=M. scaphocuneiformis.=--A small muscle lying on the sole of the foot in
the depression between the lateral cuneiform, medial cuneiform, and the
lateral tubercle of the scaphoid. It is hidden by the overlying
ligaments.

_Origin_, the lateral tubercle of the scaphoid bone. It passes distad
and laterad.

_Insertion_, the lateral surface of the medial cuneiform.

_Action._--Rotates the medial cuneiform on the scaphoid and would thus
act as an opponens of the great toe if the great toe were present.



THE VISCERA.


I. THE BODY CAVITY.

The greater part of the viscera are situated in the body cavity or
cœlom. This is divided by the diaphragm into two parts, the =thoracic
cavity= and the =abdominal cavity=. Each is lined by a serous membrane,
in which the part covering the outer wall of the cavity is distinguished
as the =parietal layer= from the part covering the viscera, which is
known as the =visceral layer=.

The thoracic cavity is bounded by the thoracic vertebræ, the ribs, the
sternum, and the diaphragm. The cranial opening of the cavity is filled
by the trachea and œsophagus as they enter from the neck region. The
thoracic cavity is lined by two thin layers of tissue, the outer one of
which is the =fascia endothoracica=, while the inner is the =pleura=.
The fascia endothoracica is a sheet of connective tissue which lines the
entire inner surface of the thoracic cavity, descending from the dorsal
median line to the heart, and passing into the fibrous layer of the
pericardium. The pleura is a thin membrane covering the fascia
endothoracica and corresponding to the peritoneum of the abdominal
cavity. It forms two sacs, the =pleuræ=, lining respectively the right
and left halves of the thoracic cavity. Each of these two sacs is
closed, the viscera being suspended within them by folds of the
membrane, so that the cavity is everywhere separated from the viscera by
a sheet of the pleura. That portion of the pleura which lines the
thoracic wall is known as the parietal layer; it may be divided into
that covering the ribs (=costal= pleura), and that covering the
diaphragm. That portion which covers the viscera is the visceral layer,
or, since it covers chiefly the lungs, it may be distinguished as the
=pulmonary= pleura. The medial walls of the two pleural sacs come in
contact in the median plane, forming a median vertical partition
passing lengthwise of the thoracic cavity. This partition is known as
the =mediastinal septum=. The space between the two layers which make up
the mediastinal septum is known as the mediastinum, or mediastinal
cavity; it contains numerous organs of the thorax. Three parts are
usually distinguished in this cavity: a =ventral= mediastinal cavity,
containing chiefly blood-vessels and the thymus gland; a =middle=
mediastinal cavity, enclosing the heart and the anterior and posterior
venæ cavæ; and a =dorsal= mediastinal cavity, containing the trachea,
the œsophagus, and the aorta.

The abdominal cavity lies caudad of the diaphragm; in it are sometimes
distinguished the =abdominal cavity proper=, extending as far caudad as
the cranial edge of the pubis, and the =pelvic= cavity, lying caudad of
this, in the region surrounded by the innominate bones and the sacrum.
The two cavities are not distinctly marked off, so that it is convenient
to consider the abdominal cavity as undivided. Both parts are lined by
the =peritoneum=.

The =peritoneum= is a thin transparent sheet of connective tissue
supporting on its surface a layer of flattened epithelial cells, the
peritoneal epithelium. It forms a sac which lines the entire abdominal
cavity. This sac is closed in the male; in the female, however, it
communicates with the exterior through the uterine (or Fallopian) tubes
and uteri. All the organs of the abdominal cavity are outside the sac.
In the course of their development these organs have encroached on the
peritoneal sac. Each has grown against the outer wall of the sac to a
greater or less extent and has forced a part of this wall ahead of it
into the cavity. In some cases the encroachment has gone so far that the
organ in question lies apparently within the peritoneal cavity,
suspended from the wall of the sac by a fold of that wall. The wall may
thus be divided into three portions. One of these, the =parietal= layer,
lines the wall of the body cavity. The second (the =mesentery= in case
of the alimentary canal, or a =ligament= in the case of another organ)
suspends the organ from the body wall. Between the layers of each
mesentery or ligament blood-vessels may pass to the organs. The third
portion or =visceral= layer covers the organ in question, forming its
=serous= covering.

The reflections of the peritoneum to form the mesenteries and ligaments
may be thus described:

Caudally the peritoneum covers the whole surface of the bladder and is
reflected from its ventral wall to the linea alba as the =suspensory
ligament= of the bladder. Farther craniad the peritoneum suspends the
rectum and colon from the middorsal line, forming the =mesorectum= and
=mesocolon=. The mesocolon continues craniad to the level of the caudal
end of the right kidney and is broadest at its cranial end. At this end
the mesocolon passes into the =mesentery= proper, which suspends the
small intestine and is very broad and much folded. Its dorsal border is
attached to the median line opposite the caudal end of the kidneys and
is very short compared to its very long ventral or intestinal border.
Toward the cranial end the mesentery of the jejunum passes gradually
into the very much shorter duodenal mesentery. This is drawn out at the
caudal end of the duodenum into a fold, the =duodenorenal= ligament
which attaches the duodenum to the kidney.

The =mesogastrium= or peritoneal fold for the stomach passes from that
part of the median dorsal line lying between the kidneys and the
diaphragm, to the greater curvature of the stomach. It does not pass
directly to the stomach, but passes first ventrad of the small intestine
as far as the pelvis. Thence it turns craniad to reach the greater
curvature of the stomach. The fold thus formed is called the =great
omentum=. It forms the dorsal and ventral walls of a sac, the =omental
sac=, the cavity of which is called the =lesser peritoneal cavity=. The
descending limb of the fold forms the dorsal wall of the sac, and its
ascending limb forms the ventral wall. Each of these walls is double
like a mesentery, so that the great omentum consists of four sheets of
peritoneum. Between the two sheets forming the descending limb lies the
left half of the pancreas, which passes thence to the right into the
duodenal mesentery. A transverse fold passes from the descending limb of
the omentum along the cranial border of the pancreas to the duodenal
mesentery. Farther to the right the descending limb of the omentum,
which is here shorter, encloses the spleen and holds it in position
parallel to the greater curvature of the stomach and about one
centimeter from it. This part of the great omentum is sometimes called
the =gastrosplenic= or =gastrolienal= omentum.

The great omental sac communicates with the peritoneal sac by an
opening, the =foramen epiploicum= or =foramen of Winslow=. This opening
lies caudad and dextrad of the caudate lobe of the liver. This lobe
itself lies within the sac. Along the ventral border of the foramen
epiploicum pass the common bile-duct from the liver and the portal vein
to the liver.

The size of the great omental sac is increased by the =lesser omentum=.
This is a double sheet of peritoneum which stretches horizontally from
the liver to the duodenum and the lesser curvature of the stomach. It
covers ventrad the caudate lobe of the liver. Its right border is at the
foramen epiploicum. The part of it which stretches to the duodenum is
called the =duodenohepatic= ligament and contains the bile-ducts and the
portal vein. The part that stretches to the stomach is called the
=gastrohepatic= ligament. The peritoneum covers the caudal and cranial
surfaces of the liver and is reflected to the adjacent parts to form the
ligaments of the liver.

The =suspensory= ligament of the liver passes from the caudal surface of
the diaphragm and the median ventral line for about one or two
centimeters caudad of the diaphragm, to the liver, and extends between
its two halves. The =ligamentum teres= or round ligament is the
thickened free caudal border of the suspensory ligament. It is the
remains of the fœtal umbilical vein. From the dorsal border of the liver
the peritoneum which covers its cranial surface turns ventrad onto the
caudal surface of the diaphragm, while that which covers its caudal
surface turns dorsad onto the caudal surface of the diaphragm to reach
the dorsal body wall. Between these two sheets a small linear part of
the surface of the liver is closely applied to the diaphragm without
intervening peritoneum. The two sheets which bound this area constitute
the =coronary= ligament of the liver. This ligament is broader where it
passes from the left lateral lobe to the diaphragm and is called the
=triangular= ligament. (There is perhaps a corresponding right
triangular ligament, from the cranial division of the right lateral
lobe.) The caudal division of the right lateral lobe is held to the
kidney of that side by the =hepatorenal= ligament.


II. THE ALIMENTARY CANAL. APPARATUS DIGESTORIUS.

The alimentary canal may be divided into mouth, pharynx, œsophagus,
stomach, small intestine, and large intestine. With these are associated
certain accessory structures,--the salivary glands, the liver, and the
pancreas. The spleen, though not belonging to the digestive system, is
usually described in connection with it. The respiratory organs are
almost throughout in close relation with the organs of the digestive
system.


1. =The Mouth. Cavum oris.=--The mouth cavity extends from the lips to
the pharynx. It is narrower toward the lips, broadens caudad as far back
as the last teeth, then becomes narrowed to form the =isthmus faucium=,
by which it communicates with the pharynx. The mouth cavity is divisible
into the =vestibule= of the mouth (=vestibulum oris=), which comprises
that part outside the jaws proper, bounded externally by the lips and
cheeks, and the =mouth cavity proper= (=cavum oris proprium=), which
lies within the teeth. That portion of the vestibule which is bounded by
the cheeks is sometimes farther distinguished as the =buccal cavity=.
The entire mouth cavity (except the teeth) is lined by the mucous
membrane or =mucosa=.

The =lips= (=labia oris=) are thick folds of skin bounding the entrance
to the mouth cavity. The outer surface is covered with hair; the inner
surface is covered with the mucous membrane. The upper lip is marked in
the median line by a deep external groove which extends upward to the
septum of the nose. Along the inner surface of this groove the lip is
closely united to the jaw by a thick fold, the =frenulum= of the upper
lip. For some distance on each side of the frenulum the inner surface of
the lip bears numerous large papillæ. The =lower= lip is also united to
the jaw by a frenulum in the median line; it is again united to the jaw
just caudad of the canine tooth, in the space between the latter and the
first premolar. Caudad the two lips pass into each other (forming the
=commissura labiorum=), and unite with the cheek. The muscles of the
lips have been described (page 105).

The =cheeks= (=buccæ=) in the cat are comparatively thin and small,
extending from the lips caudad to the ramus of the mandible. The outer
surface is covered with hair; the inner surface is smooth and somewhat
folded. The buccal cavity is rather small. On the inner surface of the
cheek open the duct of the parotid (Steno’s duct), the ducts of the
molar gland, and that of the infraorbital gland.

The roof of the mouth cavity is formed by the hard and soft palates. The
hard palate (=palatum durum=) forms the cranial part of the roof; it is
supported by the palatal plates of the maxillary and palatine bones.
The mucosa of the hard palate is elevated to form seven or eight curved
transverse ridges, which are concave caudad. Between the ridges are rows
of papillæ. In front of the most cranial ridge is a papilla in the
middle line, and at each side of the papilla is the opening of a small
duct (the =incisive duct= or =Stenson’s duct=), which leads dorsad
through the incisive foramen to the =vomeronasal= organ (or =organ of
Jacobson=), which lies on the floor of the nasal cavity. Caudad of the
hard palate the roof of the mouth is formed by the soft palate or =velum
palatinum=, described below.

The floor of the mouth cavity is formed chiefly by the tongue, which
extends as far caudad as the isthmus faucium. Ventrad of the free edge
of the tongue the mucosa forms a prominent median vertical fold which
unites the tongue with the floor of the mouth beneath it; this fold is
the frenulum linguæ. On each side of the median line at the cranial
border of the floor of the mouth is a prominent papilla, at the apex of
which open the ducts of the submaxillary and sublingual glands, the
former on the lateral side of the apex, the latter on the medial side.

The sides of the mouth cavity are formed by the teeth and the gums,
covering the alveolar borders of the mandible, maxillaries, and
premaxillaries.

The mouth cavity presents further for examination the =glands=, the
=teeth=, the =tongue=, and the =soft palate=.


THE GLANDS OF THE MOUTH (GLANDULÆ ORIS).--There are five pairs of
salivary glands which open into the mouth cavity.

1. The =parotid gland= (=glandula parotis=) (Fig. 65, 1; Fig. 131, 10)
is flattened, rather finely lobulated, and lies ventrad of the external
auditory meatus and beneath the dermal muscles. Its cranial border
follows the caudal border of the masseter muscle and overlies it
somewhat; its caudal border is about three centimeters caudad of the
border of the masseter. Its borders are unevenly lobed. The parotid duct
(=ductus parotideus=: frequently called =Stenon’s= or =Steno’s duct=) is
formed by the union of several smaller ducts near the ventral end of the
cranial border of the gland. It passes craniad imbedded in the fascia
covering the masseter. At the cranial border of the masseter it turns
inward and lies close against the mucous membrane of the mouth, so that
from the inside of the mouth it appears as a white ridge on the mucosa.
It opens on the inside of the cheek opposite the most prominent cusp of
the last premolar tooth. Along the course of the parotid duct in some
cases one or more small =accessory parotid glands= are found.

2. The =submaxillary gland= (=glandula submaxillaris=) (Fig. 65, 2, page
109, and Fig. 131, 11) is approximately kidney-shaped. Its surface is
nearly smooth, the lobulations not being apparent externally. It lies
ventrad of the parotid, at the caudal edge of the masseter muscle, just
caudad of the angular process of the mandible. The posterior facial vein
(Fig. 131, =b=) crosses its outer surface, and its cranioventral border
is hidden by two lymphatic glands (Fig. 131, 12) lying at the sides of
the anterior facial vein. The =submaxillary duct= (=ductus
submaxillaris=, frequently called =Wharton’s duct=) leaves the inner
surface of the gland and passes beneath the digastric and mylohyoid
muscles and against the outer surface of the styloglossus. From the
point where the styloglossus passes into the tongue the duct continues
craniad close against the oral mucosa and parallel to the mandibula. It
is accompanied by the duct of the sublingual, which lies at first dorsad
of it and then mediad. It opens at the apex of the prominent papilla
which lies at the side of the middle line at the cranial end of the
floor of the mouth.

3. The =sublingual gland= is elongated and conical in form, with its
base against the submaxillary, of which it appears to be a continuation.
It stretches along the submaxillary duct for about one and one-half
centimeters, lying between the masseter and digastric muscles. The
=sublingual= duct leaves its ventral side, passes close to the
submaxillary duct, at first dorsad and then mediad of it, and opens on
the medial side of the apex of the same papilla with the submaxillary
duct.

4. =The molar gland= (=glandula molaris=) (Fig. 65, 9) lies between the
orbicularis oris and the mucosa of the lower lip. It stretches from the
cranial border of the masseter to a point between the first premolar and
the canine. It is flat, broad caudad, and ends in a point craniad. It
has several ducts which pass straight through the cheek and open on the
mucous surface of the mouth.

5. The =infraorbital= (or =orbital=) =gland= lies in the lateral part of
the orbit on its ventral floor. It is ovoid and about one and one-half
centimeters long and one-third as thick. Its ventral end rests against
the mucosa of the mouth just caudad of the molar tooth. Its duct leaves
the ventral end and opens into the mouth at a point about three
millimeters caudad of the molar tooth.


THE TEETH. DENTES.--The adult cat has thirty teeth, fourteen in the
lower jaw and sixteen in the upper jaw. There are twelve =incisors=,
four =canines=, ten =premolars=, and four =molars=. The tooth formula
for the cat is then

     3 - 3     1 - 1      3 - 3     1 - 1
  _i_-----, _c_-----, _pm_-----, _m_-----.
     3 - 3     1 - 1      2 - 2     1 - 1

The teeth are implanted in the alveolar borders of the premaxillaries,
maxillaries, and mandible. In each tooth can be distinguished the
=root=, imbedded in the socket of the bone, the =crown=, which projects
above the gums, and a narrow =neck= connecting the two. The root is
composed of one or more separate fangs; the crown bears one or more
points or cusps.

At the cranial end of each jaw are six =incisor= teeth (Figs. 93 and 94,
_a_). These are imbedded in the alveolar borders of the premaxillaries
and the mandible. The incisor teeth are small, with a crown bearing a
sharp edge which is notched so as to form three minute cusps. The root
of each has a single fang. The lateral incisors are the largest in each
jaw, and those of the upper jaw are larger than those of the lower.

  [Illustration: FIG. 93.--UPPER JAW, WITH ROOTS OF THE TEETH LAID BARE.

  _a_, incisors; _b_, canine; _c_, first premolar; _d_, second premolar;
  _e_, third premolar; _f_, molar.]

Caudad of the incisors, and in the upper jaw separated from them by a
slight interval, are the =canines= (_b_), two in each jaw. These are
long, strong, pointed teeth, deeply imbedded in the mandible and
maxillaries, their large sockets causing a rounded swelling on the
external surface of the bones. Each has a single fang and a single cusp.
When the mouth is closed the upper canines lie laterocaudad of the lower
ones.

Caudad of the canines there is in each jaw a considerable interval free
from teeth: this is called the =diastema=. Caudad of the diastema are
the =premolar= teeth, three pairs (_c_, _d_, _e_) in the upper jaw and
two pairs (_c_, _d_) in the lower jaw. These teeth are compressed
sideways, and those of the lower jaw fit inside of those of the upper
jaw. In the =upper= jaw (Fig. 93) the first premolar (_c_) is small and
usually has but a single cusp and a single fang, though occasionally
there is a small supplementary cusp and fang. The second premolar is
larger (_d_); it has a large central cusp, with a single smaller cranial
cusp and two small caudal cusps, making four in all. This tooth has two
fangs. The third premolar (_e_) is the largest tooth in the jaws; it has
three large cusps in longitudinal series and a small cusp lying on the
medial side of the first one in the row. Its root has three fangs. The
=molar= tooth (_f_) of the upper jaw is small and lies caudomediad of
the last premolar. It has two small cusps and two fangs.

  [Illustration: FIG. 94.--MANDIBLE, WITH ROOTS OF THE TEETH LAID BARE.

  _a_, incisors; _b_, canine; _c_, first premolar; _d_, second premolar;
  _f_, molar.]

In the =lower= jaw (Fig. 94) the two premolars (_c_ and _d_) are
similar, the caudal one being a little larger. Each has four cusps; a
single large one, a small one craniad of this, and two small ones caudad
of it. Each has two fangs. The single molar (_f_) is the largest tooth
of the lower jaw; it has two large cusps and two fangs.

=The Deciduous Teeth.=--At birth the cat has no teeth. There appears
later a set of twenty-six teeth: twelve incisors, four canines, and ten
molars (six in the upper jaw and four in the lower). These teeth are
later replaced by the permanent ones above described. The deciduous
teeth of the cat are fully described by Jayne (“Mammalian Anatomy,” vol.
1. p. 319), where also an account is given of the order of appearance of
the teeth.


THE TONGUE. LINGUA (Fig. 95).--The =tongue= is a muscular organ covered
with mucous membrane; in life it is very mobile. It is an elongated
organ, flat above, broadest in the middle, and very slightly narrowed at
each end. It extends from the incisor teeth to the isthmus faucium and
nearly fills the mouth cavity. The caudal third of the tongue forms the
floor of the mouth cavity, so that the tongue has here no ventral
surface, but is directly continuous with underlying organs. It is in
this region that the extrinsic muscles of the tongue (except the
genioglossus) enter it. The cranial two-thirds of the tongue is partly
or entirely free from the floor of the mouth, the cranial one-third
being completely free and movable. In about the middle third the ventral
surface of the tongue is held to the floor of the mouth by the fold
known as the =frenulum linguæ=. The frenulum contains parts of the two
genioglossus muscles, which enter the tongue through it. The ventral
surface and lateral borders of the tongue are smooth, soft, and free
from papillæ. The dorsal surface is raised into papillæ of various
kinds, and has a slight median longitudinal furrow. The caudal part of
the dorsal surface is softer, redder, and marked with papillæ of a
different kind from those of the rest of the tongue. From the caudal
end a small median vertical fold, the =frenulum= (or =plica=)
=glossoepiglottica= passes from the dorsal surface of the tongue to the
cranial surface of the epiglottis.

  [Illustration: FIG. 95.--TONGUE, EPIGLOTTIS, AND OPENING OF LARYNX.

  _a_, filiform papillæ; _b_, fungiform papillæ; _b′_, very large
  papillæ at the sides of the tongue; _c_, circumvallate papillæ; _d_,
  tonsils; _e_, epiglottis; _f_, plica aryepiglottica; _g_, arytenoid
  cartilages (covered with mucosa); _h_, glottis; _i_, false vocal
  cords; _j_, true vocal cords.]

The =papillæ= of the tongue are of three kinds. 1. The very numerous
=filiform papillæ= (_a_) (=papillæ filiformes=); many of them are horny
and tooth-like, with points turned caudad. These are most numerous at
the middle of the free end of the tongue. 2. The =fungiform papillæ=
(_b_) (=papillæ fungiformes=) are found scattered over the surface of
the middle of the tongue caudad of the large filiform papillæ. They are
enlarged at their free ends. There is a prominent row of very large ones
(_b′_) opposite the circumvallate papillæ at the borders of the tongue.
3. The =circumvallate papillæ= (_c_) (=papillæ vallatæ=) are blunt and
each is surrounded by a trench which is bounded in turn by a raised
wall. They are in two rows of two or three each, which converge near the
base of the tongue so as to form a V with the apex directed caudad.


MUSCLES OF THE TONGUE (Fig. 96).--=M. genioglossus= (_f_) passes from
the symphysis of the lower jaw into the tongue and lies beneath (dorsad
of) the geniohyoid (_g_).

_Origin_ from the medial surface of the mandible near the symphysis and
dorsad of the origin of the geniohyoid.

_Insertion._--The fibres pass dorsad, diverging in a fan-like manner and
forming a flat vertical plate closely applied to the muscle of the
opposite side. This plate extends along the caudal three-fourths of the
tongue, i.e. as far as it is attached. The cranial fibres arch craniad
to the tip of the tongue, the caudal fibres arch caudad to the root of
the tongue. Dorsad the muscle is confounded with the muscle of the
opposite side.

_Action._--Draws the root of the tongue forward and the tip backward.

=M. hyoglossus= (_h_).--From the body of the hyoid bone to the tongue.

_Origin._--(1) From the ventral surface of the body of the hyoid laterad
of the geniohyoid (_g_), and (2) by a second head from the ceratohyal.

_Insertion._--Both heads penetrate into the tongue between the
styloglossus (_e_) and the genioglossus (_f_). The fibres intermingle
with those of the styloglossus (_e_) and thus help to form the lateral
parts of the tongue. They finally end in the integument on the dorsum of
the tongue at the sides.

_Action._--Retracts the tongue and depresses it.

=M. styloglossus= (_e_).--From the stylohyal bone to the tongue.

_Origin_ from the mastoid process of the temporal bone, from the
stylomandibular ligament (2) (which connects the border of the external
auditory meatus with the angular process of the mandible) and from the
proximal cartilaginous portion of the cranial cornu of the hyoid bone.
The fibres pass mediad, diverging between those of the digastric and
hyoglossus (_h_) into the lateral part of the tongue.

_Insertion._--The fibres pass toward the tip of the tongue, where the
mass finally ends in a point, the superficial ones gaining insertion
into the integument at the sides of the tongue.

_Relations._--Outer surface with the digastric (Fig. 65, _b_) and
mylohyoid (Fig. 65, _c_). Inner surface with the pterygoideus internus
(Fig. 96, _d_), the cranial cornu of the hyoid, and the tympanic bulla.

_Action._--Retracts the tongue and raises it.

  [Illustration: FIG. 96.--MUSCLES OF TONGUE, HYOID BONE, AND PHARYNX.

  _a_, M. tragicus lateralis; _b_, M. jugulohyoideus; _c_, M.
  pterygoideus externus; _d_, partially cut surface of M. pterygoideus
  internus; _e_, M. styloglossus; _f_, M. genioglossus; _g_, M.
  geniohyoideus; _h_, M. hyoglossus; _i_, M. glossopharyngeus; _j_, M.
  constrictor pharyngis medius; _k_, M. constrictor pharyngis inferior;
  _l_, M. stylopharyngeus; _m_, M. sternohyoideus (cut); _n_, M.
  cricothyreoideus; _o_, M. sternothyreoideus (cut); _p_, M.
  thyreohyoideus. 1, mandible; 1′, angular process of mandible; 2,
  stylomandibular ligament; 3, bulla tympani; 4, trachea; 5, œsophagus;
  6, thyroid gland; 7, isthmus of the thyroid gland.]

The =intrinsic muscles= of the tongue (those entirely within it) are
attached to its integument at both their ends. There are three sets of
fibres: a longitudinal, a transverse, and a vertical one. These are seen
most readily in cross-sections.


THE SOFT PALATE. VELUM PALATINUM (Fig. 66, page 112).--The soft palate
is the free curtain-like structure which forms the caudal part of the
roof of the mouth. It is attached to the caudal border of the palatal
plates and the ventral border of the perpendicular plates, of the
palatine, and to the pterygoid processes and hamuli of the sphenoid, and
extends some distance caudad of the hamuli. It thus forms a rather long
and narrow curtain separating the caudal part of the nasal cavity from
the mouth. Caudad it ends in a free arched border (Fig. 66, 4) which is
at about the level of the epiglottis, and may lie against the cranial or
the caudal surface of the latter. The narrowed passage bounded by the
margin of the velum palatinum dorsad and the tongue ventrad is the
=isthmus faucium=. From the sides of the velum a short distance from the
caudal border a fold of mucosa passes ventrad to the side of the tongue;
a short distance caudad of this a similar fold passes to the floor of
the pharynx. These folds form the cranial and caudal =pillars of the
fauces=. Between these folds is a shallow pocket, from the bottom of
which there arises a prominent projection or swelling which is one of
the two =tonsils= (Fig. 95, _d_). Each tonsil is a reddish, lobulated
gland, lymphoid in the adult, nearly a centimeter in length, and about
one-third as long as broad, with its long axis craniocaudad.

The velum palatinum consists of two layers of mucous membrane, oral and
nasal, with intervening muscular and connective tissue. The muscles of
the soft palate in the cat are as follows:

=M. tensor veli palatini= (Fig. 66, _d_, _d′_, page 112).

_Origin_ from the ventral surface of the body of the sphenoid between
the foramen ovale and the groove for the Eustachian tube. The muscle
ends in a flat tendon which passes over the hamular process (3) of the
pterygoid bone.

_Insertion_ by spreading out in the soft palate into an aponeurosis
which joins the aponeurosis of the opposite muscle and lies between the
mucous membrane of the mouth and that of the nose.

_Action._--Stretches the palate.

=M. levator veli palatini= (Fig. 66, _e_, _e′_).--A flat triangular
muscle which lies within the tensor.

_Origin_ from the surface of the body of the sphenoid mediad of the
groove for the Eustachian tube, from the styliform process of the bulla
tympani, and in part from the Eustachian tube. The muscle passes caudad,
and its fibres then diverge into the velum palatinum.

_Insertion_ into the velum palatinum, some of the fibres meeting in the
middle line.

_Action_ indicated by the name.

A number of other muscles have been described in the soft palate of the
cat; they are, however, poorly developed and not easily distinguished.
For an account of these, see Stowell, Proceedings of the Am. Soc. of
Microscopists, 1889.


2. =The Pharynx.=--At the caudal end of the mouth cavity the passage
for the food and that for the air cross; at the cranial end the
food-passage (mouth) is ventral, the respiratory passage (nasal cavity)
dorsal. Farther caudad the food-passage (œsophagus) is dorsal, while the
respiratory passage (larynx and trachea) is ventral. In the region of
crossing there is therefore for a certain distance a common passageway
for food and air, and this is known as the =pharynx=. It extends from
the isthmus faucium, at the free caudal margin of the soft palate, to
the beginning of the œsophagus, at the dorsal or caudal margin of the
opening of the larynx. The dorsal wall of the pharynx is separated from
the base of the skull and the centra of the cervical vertebræ only by
intervening muscles (=longus capitis=, =levator scapulæ ventralis=, and
=longus colli=, Fig. 72, page 143). Its lateral and ventral walls are
supported by the hyoid bone and the cartilages of the larynx.

Craniad the pharynx continues, usually, without break into the cavity
lying dorsad of the soft palate. But at the time of swallowing the free
edge of the soft palate is pushed dorsad against the dorsal wall of the
pharynx, while the caudal part of the pharynx is drawn craniad, so as to
form a cavity continuous with that of the mouth. In this way the cavity
above the soft palate is completely separated at the time of swallowing
from the rest of the pharynx. This separated portion is known as the
=nasopharynx=: it is strictly a portion of the respiratory passage, as
the food does not pass into it. The nasopharynx is continuous craniad by
the =choanæ= with the nasal cavity; it forms a horizontal tube between
and ventrad of the perpendicular plates of the palatine bones, and has
the same craniocaudal extent as the soft palate. Its dorsal wall lies
against the basis cranii and the longus capitis muscles; its lateral
walls against the pterygoid muscles and the perpendicular plates of the
palatine bones; its ventral wall is the soft palate. At the middle of
its length, at the junction of its dorsal and lateral wall, are two
longitudinal slits about three millimeters long. These are the medial
openings of the =Eustachian tubes=, by which the nasopharynx
communicates with the tympanic cavity.

The =pharynx proper=, situated caudad of the nasopharynx, is smaller
than the latter. It is bounded craniad by the epiglottis and the margin
of the soft palate, and is continuous between the two, by the isthmus
faucium, with the mouth cavity. Its floor is formed by the cranial end
of the larynx. At its caudal end it passes dorsally into the œsophagus,
while ventrally it communicates with the larynx. Its walls are muscular.


MUSCLES OF THE PHARYNX (Fig. 96).--=M. glossopharyngeus= (_i_).

_Origin._--Some fibres on the ventral and lateral part of the
genioglossus (_f_) leave that muscle near its caudal end. They form a
thin band of diverging fibres which pass outside of the cranial horn of
the hyoid. A similar sheet of fibres leaves the midventral part of the
styloglossus (_e_). The two sheets unite and the united muscle crosses
the hyoid, turns dorsad, and has its

_Insertion_ into the median dorsal raphe of the pharynx.

_Action._--Constrictor of the pharynx.

=M. constrictor pharyngis inferior= (_k_).--A thin sheet of muscle
covering the sides of the pharynx at its caudal end.

_Origin_ from the lateral surfaces of the thyroid and the cricoid
cartilages. The fibres pass dorsad and craniad, the cranial ones
covering the fibres of the middle constrictor (_j_).

_Insertion._--The median longitudinal raphe on the dorsum of the
pharynx. The caudal fibres are transverse and continuous with the
circular fibres of the œsophagus. The cranial fibres may pass as far as
the base of the sphenoid.

_Action._--Constrictor of the pharynx.

=M. constrictor pharyngis medius= (_j_).--A thin sheet which covers the
middle part of the lateral surface of the pharynx.

_Origin._--The ventral two pieces of the cranial horn and the whole of
the caudal horn of the hyoid. The fibres diverge, passing dorsad.

_Insertion_ into the median dorsal raphe of the pharynx. The cranial
fibres are inserted into the base of the sphenoid bone. The muscle
covers part of the stylopharyngeus (_l_) and the superior constrictor
(Fig. 66, _f_, page 112) and is partly covered by the glossopharyngeus
(Fig. 96, _i_).

_Action._--Constrictor of the pharynx.

=M. stylopharyngeus= (_l_).

_Origin_ from the tip of the mastoid process of the temporal bone and
from the inner surface of the cartilaginous piece between the
tympanohyal and the stylohyal bones. The parallel fibres form a flat
band which passes ventrocaudad over the outer surface of the constrictor
superior.

_Insertion._--The ventral fibres pass beneath the middle constrictor
(_j_) at its cranial border and, continuing toward the middle line of
the pharynx, gradually lose themselves among the fibres of the superior
constrictor. The dorsal fibres pass onto the outer surface of the middle
constrictor and are lost among its fibres.

_Action._--Constrictor of the pharynx.

=M. constrictor pharyngis superior= or =pterygopharyngeus= (Fig. 66,
_f_, page 112).--A flat, triangular sheet beneath the constrictor
medius.

_Origin._--The tip of the hamular process of the pterygoid bone. The
muscle passes caudad, the fibres diverging, and dips beneath the cranial
border of the constrictor medius.

_Insertion_ into the median dorsal raphe of the pharynx. The dorsal
fibres are inserted into the base of the sphenoid. The ventral fibres
pass lengthwise of the pharynx, closely connected with those of the
stylopharyngeus (Fig. 96, _l_), and finally reach the level of the
larynx.

_Action._--Constrictor of the pharynx.


3. =The Œsophagus.=--The œsophagus is a straight tube, dorsoventrally
flat when empty, which extends from the pharynx to the stomach. It has a
uniform diameter when moderately dilated of about one centimeter. It
lies dorsad of the trachea and against the longus colli muscles (Fig.
72, _g′_) covering the centra of the cervical vertebræ, until it reaches
the caudal end of the thyroid gland (Fig. 96, 6); then it passes to the
left and lies laterodorsad of the trachea until it reaches the
bifurcation of the trachea. It there returns to the median line, passes
gradually distad, separated from the vertebræ by the aorta, and finally
pierces the diaphragm about two centimeters from the dorsal body wall,
and enters the stomach. Its attachment to the diaphragm is loose enough
to permit of longitudinal motion. In passing through the thoracic cavity
it lies in the posterior mediastinum ventrad of the aorta. Its wall
consists of a muscular coat, a submucosa, and a mucosa, and its inner
surface presents many longitudinal folds. It has no serous covering, its
side walls being merely in contact with the halves of the mediastinal
septum.


4. =The Stomach. Ventriculus= (Fig. 97).--The stomach is the widest part
of the alimentary canal. It is a pear-shaped sac, the long axis of which
is curved nearly into a semicircle. The broad end of the sac lies to the
left and dorsad; here the stomach communicates with the œsophagus (_a_).
The narrowed end extends to the right and lies more ventrad than the
other end; it passes here into the duodenum (_g_). That portion of the
stomach which communicates with the œsophagus is known as the =cardiac=
end (_b_); the opposite is the =pyloric= end. Owing to the curved form
of the stomach above mentioned it is possible to distinguish a concave
and a convex side. The concave side is directed craniad and dextrad; it
is called the =lesser curvature= of the stomach (_c_). The longer convex
border is directed caudad and to the left; it is called the =greater
curvature= (_d_). The greater curvature extends to the left, next to the
œsophagus, into a prominent convexity known as the fundus (_e_) of the
stomach.

The stomach lies at the cranial end of the abdominal cavity, mostly to
the left of the middle line. Its cardiac end is in contact by its dorsal
surface with the dorsal, nearly horizontal, portion of the diaphragm. On
its ventral side the cardiac end does not touch the diaphragm, so that a
small part of the œsophagus passes here for a short distance into the
abdominal cavity, to join the stomach. The communication of œsophagus
and stomach is by a simple conical increase in size of the former. The
pyloric end of the stomach extends to the right of the middle line,
becoming constantly smaller; at its junction with the duodenum there is
a constriction which marks the position of the =pyloric valve= (_f_).
This valve is formed by a ring-like thickening of the circular
muscle-fibres of the alimentary canal, forming a sphincter muscle at the
junction of the stomach and duodenum and causing a projection of the
mucosa into the lumen of the canal. The ventral surface of the stomach
lies against the liver except when the stomach is much distended with
food, when the ventral surface comes to lie against the ventral
abdominal wall.

  [Illustration: FIG. 97.--STOMACH, VENTRAL VIEW.

  _a_, œsophagus; _b_, cardiac end of the stomach; _c_, lesser
  curvature; _d_, greater curvature; _e_, fundus; _f_, pyloric valve;
  _g_, part of duodenum.]

The stomach is supported by the =great omentum= and the =gastrohepatic=
ligament. It is connected with the duodenum by the =gastroduodenal=
ligament; with the spleen by the =gastrolienal= ligament.

The inner surface of the stomach presents longitudinal folds at its
pyloric end and along the greater curvature as far as the fundus. The
prominence of these depends on the degree of distension. Its walls are
composed of an external peritoneal layer, an internal mucous layer, and
an intervening muscular layer. This may be seen with the unaided eye in
sections of the wall.


5. =The Small Intestine. Intestinum tenue.=--The small intestine lies in
numerous coils which take up the greater part of the space in the
abdominal cavity. It has a length about three times that of the body of
the cat. It is usually considered as divided into three parts,
=duodenum=, =jejunum=, and =ileum=; these divisions are, however, not
clearly marked off. The small intestine is suspended by the =mesentery=
already described.

The =duodenum= is that part of the small intestine which follows the
stomach. At the pylorus (Fig. 97, _f_) the alimentary canal makes a
rather sharp turn so that the first part of the duodenum forms an angle
with the pyloric portion of the stomach, and extends caudad and slightly
toward the right, soon becoming directed almost entirely caudad and
lying along the right side. About eight or ten centimeters caudad of the
pylorus it makes a U-shaped bend, extending thus craniosinistrad for
four or five centimeters. Here it passes without definite limit into the
jejunum, the duodenum being considered to end at the next turn caudad.
The entire duodenum is about fourteen to sixteen centimeters in length.
Between the two limbs of the U-shaped bend formed by the duodenum, the
duodenal half of the pancreas is enclosed (Fig. 102, _a_).

The walls of the duodenum are composed of the serous (peritoneal)
investment, a muscular coat which is made up of an outer thin,
longitudinal layer of fibres and an inner thick, circular layer, a
submucous coat, and inside this a mucous coat. The mucosa is thrown up
into numerous delicate finger-like villi which give to it a velvety
appearance. On the dorsal wall of the duodenum, about three centimeters
distad of the pylorus, the mucosa presents a slight papilla, at the apex
of which is seen the oval opening of the =ampulla of Vater=. This is an
ovoid space in the wall of the duodenum. The space is encroached upon by
numerous folds of the walls. The common bile-duct and the pancreatic
duct open into it, the former extending from the bottom of the ampulla
nearly to its mouth, and the latter extending from the bottom about
half-way to the mouth. Two centimeters caudoventrad of the opening of
the ampulla of Vater is the opening of the accessory pancreatic duct. It
can usually be demonstrated only by passing a bristle into the duodenum
through an opening in the duct.

The =jejunum= is the part of the small intestine following the duodenum.
It is not separated from the part of the small intestine following it by
any sharp line. In man it constitutes two-fifths of the small intestine
exclusive of the duodenum, and is characterized by its emptiness after
death and by the absence from it of Peyer’s agminated glands (Peyer’s
patches).

The =ileum= is the portion of the small intestine between the jejunum
and colon. It lies suspended by its mesentery in numerous folds in the
caudal part of the abdominal cavity, separated from the ventral
abdominal wall only by the great omentum. It is of nearly uniform
diameter, but its caudal portion is thinner-walled than its cranial
portion. Its walls have a microscopic structure like that of the
duodenum and jejunum. On its inner surface and on the inner surface of
the jejunum are seen close-set villi, but these become rather sparser
toward the caudal end of the ileum and disappear about one centimeter
from the opening into the colon. Among the villi of the caudal end of
the ileum are numerous rounded elongations free from villi. These are
the solitary follicles or solitary glands (lymphatic) of the intestine.
These glands when aggregated together form the agminated glands or
patches of Peyer. The ileum passes at the caudal end into the colon, the
opening being guarded by the =ileocolic valve= (Fig. 99). This is formed
by a marked projection of the mucosa (_f_) and transverse muscle layer
(_e_) of the ileum into the colon. Its surface is free from villi.


6. =The Large Intestine. Intestinum crassum=.--The large intestine is
divided into =colon= and =rectum=. The =colon= or first part of the
large intestine lies against the dorsal body wall and is separated from
the ventral body wall by the folds of the ileum. It has a diameter about
three times that of the ileum. The opening of the ileum into it is on
its side between one and two centimeters from its cranial end (Fig. 98).
The blind pouch thus formed by the cranial end of the colon is the
=cæcum= (Fig. 98, _c_; Fig. 99, _a_). The cæcum ends in a slight conical
projection which may be considered as the rudiment of a vermiform
appendix. The colon lies at first on the right side and passes at first
craniad; then transversely to the left, then caudad, lying nearly in the
middle line and next to the dorsal abdominal wall. The colon may thus be
distinguished according to its direction into =ascending, transverse,=
and =descending= colon. At its caudal end the colon passes without sharp
limit into the rectum.

  [Illustration: FIG. 98.--JUNCTION OF SMALL AND LARGE INTESTINE.

  FIG. 99.--SECTION OF THE ILEOCOLIC VALVE.

  Fig. 98.--_a_, ileum; =b=, ascending colon; _c_, cæcum; _d_, position
  of ileocolic valve.

  Fig. 99.--_a_, cæcum; _b_, colon; _c_, ileum; _d_, longitudinal muscle
  layer; _e_, transverse muscle layer; _f_, mucosa; _g_, ileocolic valve
  (opened, as when material is passing into the colon).]

At the bottom of the cæcum on its inner surface is seen a collection of
solitary glands forming one of the agminated glands of Peyer, or Peyer’s
patches. The mucous membrane is without villi. It presents a few
considerable elevations, probably solitary glands.

The =rectum= is the terminal portion of the large intestine lying in the
median line close to the dorsal body wall, from which it is suspended by
the short mesorectum. Its structure is like that of the colon. It opens
externally at the anus. The entire large intestine has a length about
one-half that of the animal. At each side of the anus are two large
secreting sacs, the =anal sacs= or =glands=, each about a centimeter in
diameter. These open into the anus one or two millimeters from its
caudal boundary.

=Muscles of the Rectum and Anus.=--Owing to the close interrelation of
the muscles of the rectum and anus with those of the urogenital organs,
all these muscles will be described together at the end of the
description of the urogenital system.


7. =The Liver=, =Pancreas=, and =Spleen=.--=The Liver.= =Hepar.=--The
liver (Figs. 100 and 101) is a large red-brown organ occupying the
cranial part of the abdominal cavity. It is closely applied to the
caudal surface of the diaphragm and extends thence ventrad of the
stomach so as to conceal all but its pyloric end. Owing to the position
of the stomach the larger mass of the liver is on the right side and it
extends somewhat further caudad on this side.

The liver is divided by the dorsoventral suspensory ligament into the
=right= and =left= lobes, and each half is again divided into lobes. On
the left is a small =left median= (_b_) and a larger =left lateral= lobe
(_a_). The left lateral (_a_) extends caudad with a thin edge which
covers the greater part of the ventral surface of the stomach. On the
right there is a large =right median= (or =cystic=) lobe (_c, c′_). Its
cranial surface is dome-shaped and fitted against the right two-thirds
of the caudal surface of the diaphragm. Its ventral edge is thin, its
dorsal edge thick, and its caudal surface marked by a deep dorsoventral
cleft in which lies the gall-bladder (Fig. 101, _f_). Dorsad and caudad
of the cystic lobe is the =right lateral= lobe (_d, d′_), which is
deeply cleft. Its elongated caudal division (_d′_) extends in a point to
the caudal end of the right kidney and is adapted to the medial half of
its ventral surface. Its smaller and more compact cranial division (_d_)
ends ventrally in a thin edge. It lies between the caudal division
(_d′_) and the cystic lobe (_c_), and its dorsal surface is adapted to
the suprarenal body. The =caudate= or =Spigelian= lobe (Fig. 101, _e_)
is an elongated, triangular, pyramidal lobe. It lies in the omental sac
and partly closes the foramen epiploicum (foramen of Winslow). At its
base it is connected with the caudal division of the right lateral lobe
(_d′_).

  [Illustration: FIG. 100.--LIVER, CRANIAL SURFACE.

  _a_, left lateral lobe; _b_, left median lobe; _c_, right median lobe;
  _d_, _d′_, right lateral lobe; _e_, gall-bladder; _f_, opening of
  posterior vena cava, with the smaller openings of the hepatic veins.]

  [Illustration: FIG. 101.--LIVER TURNED CRANIAD, SHOWING DORSOCAUDAL
  SURFACE.

  _a_, left lateral lobe; _b_, left median lobe; _c_, _c′_, right median
  (or cystic) lobe; _d_, _d′_, cranial and caudal divisions of the right
  lateral lobe; _e_, caudate lobe; _f_, gall-bladder; _g_, cystic duct;
  _h_, hepatic ducts; _i_, common bile-duct; _j_, portal vein; _k_, part
  of duodenum.]

The =Gall-bladder= (Fig. 101, _f_) is pear-shaped and lies in a cleft on
the caudal (or dorsal) surface of the right median lobe (_c_, _c′_) of
the liver. Its larger end is directed caudad (or ventrad) and is free.
By one surface it is in contact with the liver and not covered by
peritoneum, while the other surface is covered by peritoneum. The
peritoneum in passing from the larger free end to the liver forms one or
two ligament-like folds. By its smaller end the gall-bladder is
continuous with the =cystic duct= (_g_). This duct is about three
centimeters long and has a sinuous course. At its distal end it is
joined by two (or more) =hepatic ducts= (_h_), bringing the bile from
the lobes of the liver. The relation of these to the cystic duct varies.
They may open into it by a common trunk or separately. Of these hepatic
ducts one is made up by the junction of smaller hepatic ducts from the
left half of the liver and the left half of the cystic lobe, while the
other is similarly formed by smaller ducts from the right half of the
cystic lobe, from both divisions of the right lateral lobe and from the
caudate lobe. The duct formed by the junction of the hepatic and cystic
ducts is the =common bile-duct= (=ductus communis choledochus=) (_i_).
It passes in the free right border of the gastroduodenal omentum to the
duodenum (_k_) and opens into it by way of the ampulla of Vater, in
common with the pancreatic duct, at a point on the dorsal surface of the
duodenum and about three centimeters from the pylorus.

=Pancreas.=--The pancreas (Fig. 102, _a_) is a flattened, closely
lobulated gland of irregular outline, about twelve centimeters long,
varying in width from one to two centimeters. It is bent nearly at right
angles at about its middle. One of the halves (_a′_) into which it is
divided by its bend lies in the descending limb of the great omentum,
and is near the greater curvature of the stomach (_d_) and parallel to
it. The free end of this half is in contact with the spleen (_e_). The
other half (_a_) lies in the duodenal omentum between the limits of the
duodenal U (_c_) and reaches to the bottom of the U. The pancreas has
two ducts. The larger =pancreatic duct= (_b_) (sometimes known as the
duct of Wirsung) collects the pancreatic fluid from both halves of the
gland, the ductlets from each half uniting to make two larger ducts,
which then unite near the angle of the gland to make the pancreatic
duct. This is short and broad and opens into the ampulla of Vater
together with the common bile-duct. The =accessory pancreatic duct=
(duct of Santorini) opens into the duodenum about two centimeters
caudoventrad of the ampulla of Vater. It is formed by the union of
branches which anastomose with those of the pancreatic duct. It is
apparently sometimes lacking.

  [Illustration: FIG. 102.--PANCREAS AND SPLEEN.

  The œsophagus has been cut and the stomach turned caudad, so that the
  dorsal surface of the stomach and the ventral surface of the duodenum
  are seen. _a_, pancreas (_a_, duodenal portion; _a′_, gastric
  portion); _b_, pancreatic duct; _c_, duodenum; _d_, stomach; _e_,
  spleen.]

=Spleen. Lien.=--The spleen (Fig. 102, _e_) is a deep red, flattened,
elongated gland belonging to the lymphatic system. One of its ends, the
left, lies against the free end of the gastric half of the pancreas and
is broader than the other end. The spleen is curved and is suspended in
the descending limb of the great omentum so that it follows the greater
curvature of the stomach (_d_).


III. RESPIRATORY ORGANS. APPARATUS RESPIRATORIUS.

The =organs= of =respiration= consist of the =nasal cavity=, the
=nasopharynx=, the =pharynx= (also a food-passage), the =larynx= (also
the organ of the voice), the =trachea=, the =bronchi=, and the =lungs=.
With them are usually described also the =thyroid= and =thymus glands=.


1. =The Nasal Cavity. Cavum nasi.=--The osseous framework of the nasal
cavity has already been described (page 59), and in connection with this
description the boundaries of the cavity and its connections with other
cavities have been given. It consists essentially of a large cavity
bounded by the facial bones and divided by a longitudinal partition into
two lateral halves. The two cavities thus formed are nearly filled by
(1) the labyrinths of the ethmoid (ethmoturbinals), (2) the superior
nasal conchæ or nasoturbinals, projecting into the dorsal part from the
ventral surface of the nasal bones, and (3) the inferior nasal conchæ,
or maxilloturbinals, projecting into the ventral portion from the medial
surfaces of the maxillaries.

There remain to be considered, in addition to the bones, the
=cartilaginous= framework of certain parts of the nose, and the =mucous
membrane=. The lamina perpendicularis is continued by cartilage,
especially craniad, in such a way as to make a complete septum
separating the two cavities. This septum extends from the septum of the
external nose caudad to the lamina cribrosa, and from the internasal
suture ventrad to the vomer and the suture of the premaxillaries. All
parts of the nasal cavity are lined by mucous membrane. This is
continuous at the nares with the integument, while at the choanæ it
passes into the mucosa of the pharynx. It covers the conchæ nasales and
the labyrinths of the ethmoid, passing into the cellules of the latter.
Owing to the crowding together of the conchæ nasales and the labyrinths
the nose is almost completely filled, only three narrow passageways
being distinguishable. The ventral one of these, known as the =ventral=
or =inferior meatus= of the nose, lies ventrad of the inferior nasal
concha, next to the nasal septum. It passes caudad beneath the
horizontal plate formed by the vomer and ethmoid, and opens caudad at
the =choanæ= into the nasopharynx. The =dorsal= or =superior meatus= of
the nose lies just ventrad of the superior nasal concha, next to the
median septum; it leads to the frontal sinus, the lamina cribrosa, and
the caudal parts of the ethmoid. The =middle meatus= of the nose has
almost disappeared in the cat; it is simply the narrow space between the
superior and inferior meati. It is practically filled by the ethmoid,
into the cells of which it leads. The mucosa is continued from the nasal
cavity into the sinuses of the frontals and presphenoid.

At the sides of the nasal septum, near the ventral edge, and about one
to one and a half centimeters caudad of the nares, there is on each side
a small curved cartilaginous tube, about one centimeter or less in
length. This, the =vomeronasal= organ, or =organ= of =Jacobson=, lies
against the septum, between it and the mucosa. It begins at the incisive
canal or anterior palatine foramen, in the roof of the mouth, curves
thence caudodorsad close against the side of the nasal septum, and ends
blindly in the nasal cavity.

  [Illustration: FIG. 103.--CROSS-SECTION OF THE CARTILAGES OF THE
  EXTERNAL NOSE.

  _a_, cartilage of the median septum; _b_, “wings”; _c_, ridge formed
  by internal portion of wing.]

The =nares= or cranial openings of the nasal cavity are supported by a
number of cartilages which form the framework of the =snout= or external
nose. The cartilaginous continuation of the lamina perpendicularis
extends some distance craniad of the tips of the nasal and premaxillary
bones, forming the septum of the external nose (Fig. 103, _a_). From the
dorsal edge of this projecting cartilaginous septum, two thin
cartilaginous wings (_b_) extend laterad, forming the dorsal wall of the
narial opening. Each then turns ventrad to form the lateral wall of the
opening, but does not form the ventral floor; instead it curves mediad
and finally dorsad, thus extending from the floor of the opening as a
prominent ridge (_c_) within the nares. The cartilaginous wing is thus
rolled into a sort of spiral, ending with a free edge within the narial
opening. From the ventral edge of the median cartilaginous septum there
are likewise lateral extensions, which form part of the ventral boundary
of the nares; these do not quite reach the ventral parts of the dorsal
wings, however, so that a small part of the narial opening is not
bounded by cartilage. A section of the narial cartilages is shown in
Fig. 103. The wings from the dorsal edge of the septum do not extend
quite to the cranial tip of the nose, so that a notch is formed on the
ventrolateral side of the nares; a section in this region would
therefore differ from that figured.

The framework of the external nose thus formed is covered externally by
thick hairless skin, containing many glands. From the ventral end of the
internarial septum a groove passes ventrad, partly dividing the upper
lip.

The inner surfaces of the cartilages are covered by the =mucosa=, which
forms a number of ridges. The narial opening is almost completely
divided by the prominent ridge which is supported by the free edge (_c_)
of the cartilaginous wing above described. This free edge is covered by
a thick layer of mucosa, and the entire ridge so formed is continuous
caudad with the inferior nasal concha. On the medial side of the partial
partition formed by this ridge and near the ventral side there begins a
slight distance caudad of the outer opening another ridge, supported by
the ventrally incurved portion of the cartilaginous ring. This soon
becomes a thick swelling; beneath it opens the lachrymal canal, and that
part of the passageway that lies ventromediad of it is the beginning of
the inferior meatus of the nose. About one or two centimeters caudad of
the external opening a third ridge projects from the dorsolateral wall
of the cavity toward the large ridge first described; dorsomediad of it
is a narrow passage which is the entrance to the =superior meatus= of
the nose.

The =olfactory mucosa=, or that part to which the olfactory nerve is
distributed, and which therefore acts as the sensory surface, is
confined to the dorsocaudal parts of the nasal cavity, in the region
occupied by the cells of the ethmoid. The air penetrates to this region
probably only by a definite act of snuffing, the inferior meatus serving
as the usual passageway of air to the lungs.

The =nasopharynx= and =pharynx= are considered under the alimentary
canal (page 231).


2. =The Larynx.=

The larynx is the enlarged upper end of the air-passage which leads from
the pharynx to the lungs. It is a box composed of pieces of cartilage
connected by ligaments and moved by muscles, and it is lined by mucous
membrane. At the root of the tongue about one centimeter caudad of the
body of the hyoid bone is the triangular leaf-like =epiglottis= (Fig.
95, _e_, page 227). When food is taken this closes the opening into the
larynx, and the food passes over it into the œsophagus. It is so curved
that its apex is directed craniad. A fold of mucous membrane, the =plica
glossoepiglottica= or =frenulum= of the epiglottis, extends from the
middle of its cranial surface to the root of the tongue, and on each
side of this fold is a depression.

From each side of the base of the epiglottis a fold, =plica
aryepiglottica= (Fig. 95, _f_), extends caudad to the base of the
arytenoid cartilage (_g_). Dorsad of this fold and separated from it by
a depression is a ridge which marks the position of the caudal hyoid
cornu. The plicæ aryepiglotticæ (_f_) and the epiglottis (_e_) form the
boundaries of the =aditus laryngis=, or opening into the larynx.

The cavity of the larynx is divided into three portions. The upper one
of these is the =vestibule= of the larynx. It is bounded caudad by two
folds of mucosa (_i_) that stretch from the caudal surface of the
epiglottis near its base to the tips of the arytenoid cartilages. These
folds are the =false vocal cords= (_i_). Their vibration is said to
produce purring. Caudad of the false vocal cords two folds of the mucosa
stretch from the apices of the arytenoid cartilages to the thyroid
cartilages, near the base of the epiglottis. These folds are nearer the
median plane than the false vocal cords. They are the =true vocal cords=
(_j_). The =middle portion= of the laryngeal cavity is that between the
true and the false vocal cords. It is produced laterally into a very
small pouch or pocket on each side, the =ventriculus=. The narrow slit
between the true vocal cords is the =glottis= (_h_). It can be narrowed
and widened by the action of muscles. The vocal cords, which bound it,
are set vibrating by currents of air transmitted from the lungs, and the
voice-sounds are thus produced. The =caudal portion= (inferior portion)
of the laryngeal cavity is that between the glottis and the first
tracheal cartilage. It is narrowed near the glottis.


CARTILAGES OF THE LARYNX (Fig. 104).--There are three unpaired
cartilages, the =thyroid= (1), =cricoid= (3), and =epiglottic= (2), and
two paired cartilages, the =arytenoids= (4).

  [Illustration: FIG. 104.--CARTILAGES OF LARYNX, WITH SIDE VIEW OF
  HYOID BONE.

  _b_, ceratohyal; _c_, epihyal; _d_, stylohyal; _e_, tympanohyal; _f_,
  thyrohyal. 1, thyroid cartilage; 2, epiglottis; 3, cricoid cartilage;
  4, arytenoid cartilage; 5, cricothyroid ligament; 6, thyrohyoid
  ligament; 7, trachea.]

The =thyroid= cartilage (=cartilago thyreoidea=) (1) has nearly the form
of a visor of a cap, but is relatively broader at its ends than a cap
visor. It forms about two-thirds the circumference of a circle, and is
so situated that it embraces the other cartilages ventrally and
laterally. Its caudal and cranial borders are oblique to its
caudocranial axis and are directed dorsocaudad. To the middle of the
cranial border is attached the epiglottic cartilage (2), and the whole
cranial margin is connected by membrane (6) to the body and caudal
cornua (_f_) of the hyoid bone. The dorsal border projects craniad into
a considerable cornu which is attached to the free end of the caudal
hyoid cornu (_f_). The border also projects caudad into a process which
articulates with a facet on the lateral surface of the cricoid cartilage
(3). In the middle of the dorsal surface is a longitudinal ridge for
attachment of the vocal cords and origin of the thyroarytenoid muscles
(Fig. 105, _d_), and at the caudal end of this ridge the caudal border
presents a considerable rounded notch.

The =cricoid cartilage= (=cartilago cricoidea=) (3) has the form of a
seal ring with its broader part dorsad. The broad dorsal part of the
ring is partly embraced by the wings of the thyroid cartilage (1). Its
caudal border is undulating and nearly at right angles to its
caudocranial axis. It is connected by membrane with the first tracheal
ring. The cranial border is oblique to the long axis and lies in a plane
which passes from the ventral side craniodorsad. Near the median line on
each side it articulates by an oblique facet with one of the two
arytenoid cartilages (4). Near the midventral line the cricothyroid
ligament (5) is attached and it stretches thence to the midcaudal notch
of the thyroid cartilage (1).

The outer surface presents at the middle of each side a facet for
articulation with the thyroid, and is marked in the median dorsal line
by a ridge for the posterior cricoarytenoid muscle (Fig. 105, _b_).

The =arytenoid cartilages= (=cartilago arytenoidea=) (Fig. 104, 4) are
triangular pyramids with base and sides nearly equilateral triangles.
One side articulates with an oblique facet on the cranial border of the
cricoid near the mid-dorsal line. Near the opposite apex is attached the
vocal cord. At the lateral angle of the base is attached on its dorsal
side the posterior cricoarytenoid muscle (Fig. 105, _b_), and on its
ventral side the thyroarytenoid (Fig. 105, _d_) and lateral
cricoarytenoid (Fig. 105, _c_) muscles. The movements produced by these
muscles carry the arytenoid ends of the vocal cords toward or from the
median plane and thus open or close the glottis.

The =epiglottic cartilage= (Fig. 104, 2) is flexible (fibro-cartilage)
and of a cordate form. It is so curved that its caudal surface is convex
dorsoventrally and concave from side to side. It supports the
epiglottis. Its cranial surface presents a slight median ridge for
attachment of muscles. By its base it is attached to the midventral part
of the cranial border of the thyroid cartilage (1). Its position varies
so that it either stands erect with its apex directed craniad to allow
the passage of air to the lungs, or, as in the act of swallowing, it is
turned caudad over the aditus laryngis so as to allow food to pass over
it and into the œsophagus.

The =vocal cords= are two fibrous elastic bands. Each is attached at one
end to the apex of the arytenoid cartilage, and at the other end to the
median ridge on the dorsal surface of the thyroid. Each supports a
projecting fold of mucous membrane, the vibration of which causes the
voice.


MUSCLES OF THE LARYNX.--1. Muscles moving the entire larynx.

A. =Elevators. M. thyreohyoideus= (Fig. 96, _p_, page 229).--A flat band
on the lateral side of the larynx.

_Origin_ on the lateral part of the caudal border of the thyroid
cartilage.

_Insertion_ on the medial two-thirds of the caudal border of the caudal
cornu of the hyoid.

_Action._--Raises the larynx.

The stylohyoid (Fig. 65, _d_, page 109) and the median and inferior
constrictors (Fig. 96, _j_ and _k_) of the pharynx, already described,
have the same action.

B. =Depressors.=--The sternothyroid (Fig. 65, _g′_), already described
(p. 141).

2. Muscles which move the parts of the larynx one upon another.

A. =Muscles on the Outer Surface of the Larynx.=

=M. cricothyreoideus= (Fig. 96, _n_).--A broad flat band which with its
fellow covers the ventral surface of the cricoid cartilage and the
cricothyroid ligament.

_Origin._--The lateral half of the ventral surface of the cricoid
cartilage. The muscles diverge so as to leave a part of the cricothyroid
ligament between them.

_Insertion._--The ventral part of the caudal border of the thyroid
cartilage laterad of the median ventral notch.

=M. cricoarytenoideus posterior= (Fig. 105, _b_).--The two muscles cover
the dorsal surface of the larynx.

_Origin._--From the dorsal part of the caudal border of the cricoid
cartilage (3) and from its median dorsal crest. The fibres pass
craniolaterad, converging. The lateral fibres are nearly longitudinal in
direction.

_Insertion._--The dorsal border of the caudal end of the arytenoid
cartilage (4).

_Action._--Moves the arytenoid on its oblique articulation with the
thyroid. The apex of the arytenoid is thus carried laterad, and the
vocal cords are separated so as to widen the glottis.

  [Illustration: FIG. 105.--MUSCLES OF THE LARYNX, AS EXPOSED BY REMOVAL
  OF MOST OF THE LEFT HALF OF THE THYROID CARTILAGE.

  1, epiglottis; 2, portion of the thyroid cartilage (cut); 3, cricoid
  cartilage; 4, arytenoid cartilage; 5, trachea. _a_, M. arytenoideus
  transversus; _b_, M. cricoarytenoideus posterior; _c_, M.
  cricoarytenoideus lateralis; _d_, M. thyreoarytenoideus.]

=M. arytenoideus transversus= (Fig. 105, _a_).--A small unpaired muscle
running transversely between the caudal ends of the arytenoid
cartilages, just beneath the mucous membrane and parallel to the cranial
border of the cricoid cartilage.

=M. glossoepiglotticus.=--A small longitudinal muscle, lying by the side
of its fellow in the frenulum of the epiglottis.

_Origin._--The median fibrous septum of the tongue.

_Insertion._--The dorsal (cranial) surface of the epiglottic cartilage
in the median line near its attached border.

_Action._--Draws the epiglottis craniad.

=M. hyoepiglotticus= is a small bundle of parallel fibres lying in the
frenulum of the epiglottis craniad and dorsad of the body of the hyoid
bone.

_Origin._--The lateral end of the cranial surface of the body of the
hyoid. The two muscles pass craniodorsad, converging, and unite with the
preceding.

_Insertion_ with the preceding. (The lateral portion of the muscle may
continue craniad to the tongue as a second part of the hyoglossus.)

_Action._--Like the preceding.

B. =Muscles on the Inner Surface of the Cartilages of the Larynx.=

=M. thyreoarytenoideus= (Fig. 105, _d_).--The thyroarytenoid is a
triangular, flat muscle of considerable size. It lies within the wing of
the thyroid cartilage (2), and its fibres are nearly dorsoventral in
direction.

_Origin._--The median longitudinal crest on the dorsal surface of the
thyroid cartilage (2).

_Insertion._--The fibres converge to the insertion into the cranial lip
of the laterocaudal angle of the arytenoid cartilage (4).

_Action._--Turns the arytenoid on its oblique articulation so as to
close the glottis.

=M. cricoarytenoideus lateralis= (Fig. 105, _c_).--Triangular, a little
smaller than the preceding, caudad of which it is situated, so that it
also is covered by the wing of the thyroid.

_Origin._--The lateral part of the cranial border of the cricoid
cartilage (3). The fibres converge, passing dorsad.

_Insertion._--The caudal lip of the laterocaudal angle of the arytenoid
cartilage (4).

_Action._--Similar to the preceding, so that it closes the glottis.


3. =The Trachea= (Fig. 105, 5; Fig. 106, _a_).--The trachea is that part
of the air-passage which extends from the larynx to the bronchi (Fig.
106). It is a straight tube composed of a lining mucosa with ciliated
epithelium, and a connective-tissue covering which encloses supporting
cartilages. Each tracheal cartilage is incomplete dorsally where it lies
against the œsophagus, the gap between the two free ends of each ring
being filled with muscular and connective tissue. As a result of this
the diameter of the trachea is not fixed, but can be increased and
diminished. The first ring is broader than the others. Where the
œsophagus leaves the median line, the dorsal surface of the trachea lies
against the longus colli muscles (Fig. 72, _g″_). Its ventral surface is
against the sternohyoid (Fig. 65, _e_) and sternothyroid (Fig. 65, _g′_)
muscles. Its lateral surfaces are partly covered by the thyroid gland
(Fig. 96, 6), and are in close relation with the carotid artery (Fig.
119, _a_, page 284), the vagus and sympathetic nerves (Fig. 156, _i_),
and the internal jugular vein (Fig. 119, _b_). In the thoracic cavity
the great vessels coming from the heart lie against the ventral surface
of the trachea (Fig. 129, 2). At about the level of the sixth rib the
trachea divides into the two main =bronchi= (Fig. 106). Each bronchus is
supported by incomplete rings of cartilage like those of the trachea and
has otherwise in general the structure of the trachea. In the lungs the
bronchi become divided into many branches (Fig. 106), in the manner
described in the account of the lungs.


4. =The Lungs. Pulmones.=--Immediately after division of the trachea the
two bronchi enter the lungs (Fig. 106). These are two large, much-lobed
organs, which fill the greater part of the thoracic cavity. The main
lobes of the lungs are completely separated from each other, except in
so far as they are connected by the bronchi and connective tissue; the
main lobes may also be partly subdivided into secondary lobes that are
not thus completely separated. The two lungs are completely separated
from each other, except at the =radix=, where they are united by the
bronchi; they lie in the right and left halves of the thoracic cavity,
with the mediastinal septum between them. The bronchi on entering the
lungs divide in the following manner. Each divides at first into two
main branches. The cranial branch on the right side is known as the
=eparterial= bronchus (_b_), because it lies craniad of the pulmonary
artery. All the others are =hyparterial=; i.e., they lie caudad of the
pulmonary artery. The right cranial bronchus does not further subdivide
into large bronchi, but gives off numerous small branches. The right
caudal bronchus divides into three main branches. There are thus four
main branches of the right bronchus. The left cranial bronchus divides
into two main branches; the left caudal bronchus continues caudad as a
main trunk giving off small branchlets. Of the left bronchus there are
thus but three main subdivisions. The main subdivisions of the bronchi
on the two sides correspond, as will be seen, with the lobulation of the
lungs.

The =right= lung (Fig. 106, 1-4) is slightly larger than the left
(1′-3′). It divides into three smaller proximal lobes (1-3), and one
large distal one (4). The most cranial one of the proximal lobes (1) is
sometimes partly subdivided. The third one of the proximal lobes (3)
lies mediad of the others; it is partly subdivided and one-half projects
into a pocket in the mediastinum, so that it comes to lie across the
middle line, extending a short distance onto the left side. This lobe is
frequently called the =mediastinal= lobe (3). The caudal lobe (4) of the
right lung is large and flat, containing about half the substance of the
lung.

  [Illustration: FIG. 106.--RAMIFICATIONS OF THE BRONCHI, WITH OUTLINES
  OF THE LOBES OF THE LUNGS, VENTRAL VIEW.

  1-4, lobes of the right lung; 1′-3′, lobes of the left lung. _a_,
  trachea; _b_, eparterial bronchus.]

The =left= lung is divided into three main lobes (1′-3′); the two
cranial ones (1′-2′) are, however, partly united at the base, so that
they may be considered subdivisions of but a single lobe; thus the left
lung has but two distinctly separated lobes.

Each lung is attached to the aorta, vertebral column, and diaphragm by a
fold of pleura, the =pulmonary ligament=. This is broadest at the caudal
lobe of each lung. Each pulmonary ligament is double, being formed of
two sheets of the pleura.

  [Illustration: FIG. 107.--POSITION OF THYMUS GLAND, FROM LEFT SIDE.

  _a_, heart; _b_, aorta; _c_, œsophagus; _d_, thymus gland; _e_,
  lymphatic gland; _f_, left subclavian artery; _g_, internal mammary
  artery. _I_, cut ends of first rib; _XI_, eleventh rib.]


=The Thyroid Gland. Glandula thyreoidea= (Fig. 96, 6).--The thyroid
gland consists of two lateral lobes (6) and a median lobe or =isthmus=
(7). Each lateral lobe (6) is an elongated, flattened, lobulated mass
with round ends. It is about two centimeters long and about one-fourth
as broad. It lies at the side of the trachea (4), dorsad of the lateral
margin of the sternohyoid muscle. Its cranial end is at the level of the
caudal border of the cricoid cartilage. The =isthmus= (7) is a delicate
band two millimeters wide which connects the caudal ends of the two
lateral lobes. It passes ventrad of the trachea and in close contact
with it. The thyroid has no duct.


=The Thymus Gland. Glandula thymus= (Fig. 107, _d_).--The thymus gland
is best developed in young kittens; in the adult cat it has partly or
almost completely degenerated. It is an elongated, flattened organ, of a
pinkish-gray color, which lies in the mediastinal cavity, between the
two lungs and against the sternum. It extends caudad as far as the heart
(_a_), overlying the pericardium at its posterior end. At its cranial
end it projects, when well developed, a short distance (about one
centimeter) outside of the thoracic cavity into the neck region. The
caudal end is forked, and the left lobe thus formed is usually larger
than the right. The cranial end may also show indication of a division
into two lobes, but this is frequently not the case.


IV. THE UROGENITAL SYSTEM. APPARATUS UROGENITALIS.


1. The Excretory Organs.


KIDNEY. REN (Figs. 108 and 109).

  [Illustration: FIG. 108.--LEFT KIDNEY, VENTRAL SURFACE.

  FIG. 109.--MEDIAN LONGITUDINAL SECTION OF KIDNEY.

  Fig. 108.--_a_, renal artery; _b_, renal vein; _c_, ureter.

  Fig. 109.--_a_, medullary portion; _b_, cortical portion; _c_,
  papilla; _d_, pelvis; _e_, renal artery; _f_, renal vein; _g_,
  ureter.]

The kidneys of the cat are compact (i.e., not lobulated) and have the
usual kidney or bean form. They lie in the abdominal cavity, one on
either side of the vertebral column, against the dorsal body wall, in
the region between the third and fifth lumbar vertebræ. The right kidney
is one or two centimeters farther craniad than the left, and the long
axes of the two converge craniad a little. Each is covered by peritoneum
on its ventral surface only (i.e., it is retroperitoneal). At the
border of the kidney, where the peritoneum passes from it to the body
wall, there is an accumulation of fat, which is most abundant at the
cranial end of the kidney. Within the peritoneal investment the kidney
is enclosed in a special loose fibrous covering, the =capsule= or
=tunica fibrosa=, which is continuous with the fibrous coat of the
ureter and pelvis. In the middle of the median border of each kidney is
a notch, the =hilus=. It gives exit to the ureter (Fig. 108, _c_) and
renal veins (_b_), and entrance to the renal artery (_a_). On the
ventral surface of the kidney within the capsule are seen grooves
radiating from the hilus. They contain blood-vessels. If the substance
of the kidney is sliced away parallel to the ventral surface for some
distance (Fig. 109), there is exposed a cavity, the =sinus=, which lies
near the medial border and the opening of which is the hilus. It
contains the pelvis (_d_) (the expanded beginning of the duct of the
kidney), and also renal vessels (_e_ and _f_) with their branches. These
structures are enclosed in fat, which fills the remainder of the sinus.
Upon opening the pelvis the kidney substance is seen to project into it
in the form of a cone, the =papilla= (_c_), the apex of which is
directed mediad. On the apex of the papilla are the numerous openings of
the uriniferous collecting-tubes, some of them opening at the bottom of
an apical depression of the papilla.

In a section made parallel to the ventral surface and in the median
plane, the substance of the kidney is seen to consist of a peripheral
darker and more granular =cortical portion= (Fig. 109, _b_), and of a
central, lighter, less granular =medullary portion= (_a_). Both portions
are marked by lines which converge to the apex of the papilla (_c_).


THE URETER (Fig. 108, _c_; Figs. 111 and 112, _b_).--The duct of the
kidney begins as the =pelvis= (Fig. 109, _d_), a conical sac the base of
which encloses the base of the papilla. From the apex of the papilla the
urine passes into the pelvis. The outer wall of the pelvis is continuous
with the capsule of the kidney. At the hilus the pelvis narrows to form
the =ureter= (Fig. 109, _g_). The ureter passes caudad in a fold of
peritoneum which contains fat. Near its caudal end it passes dorsad of
the vas deferens (Fig. 111, _c_), turns ventrocraniad, and pierces the
dorsal wall of the bladder (Fig. 111, _a_) obliquely near the neck. On
the inside of the bladder the openings of the ureters appear as pores
about five millimeters apart, and each is surrounded by a white,
ring-like elevation of the surface.


THE BLADDER. VESICA URINARIA.--The bladder (Fig. 111, _a_) is
pear-shaped. It lies in the abdominal cavity between its ventral wall
and the rectum and a short distance craniad of the pubic symphysis.
Caudad it is continued into a rather long, narrow =neck= (_f_) which
passes dorsad of the symphysis to the pelvic cavity.

The bladder is covered by peritoneum and is held in place by its neck
and by three folds of the peritoneum. One of these passes from its
ventral wall to the linea alba and is the =suspensory= ligament. Two
others pass one from each side of the bladder to the dorsal body wall at
the sides of the rectum. They are the =lateral= ligaments of the
bladder. They form the walls of a partly isolated peritoneal pocket into
which the rectum passes; this pocket opens craniad into the peritoneal
cavity. The wall of the bladder is composed of an internal epithelium, a
layer of plain muscle-fibre bundles which cross one another in various
directions, and the external peritoneal layer.


SUPRARENAL BODIES. GLANDULÆ SUPRARENALES.--The suprarenal bodies are two
ovoid bodies about a centimeter in the longest diameter, lying
craniomediad of the kidneys, but usually not touching them. In a fresh
condition they are of a pinkish or yellow color. They are usually
imbedded in fat and are covered by peritoneum on their ventral surface.
They have no duct and are of uncertain function.


2. The Genital Organs.


A. THE MALE GENITAL ORGANS. _External Genital Organs._--The external
genital organs are the =scrotum= and =penis=.

The =scrotal sac= or =scrotum= is a pouch of integument which lies
ventrad of the anus in the median line against the ischiatic symphysis.
It is marked by a median groove which indicates the position of an
internal septum dividing its cavity into lateral halves, within each of
which is one of the =testes=.

The =penis= (Fig. 111, _l_; Fig. 113, 6; see also page 262) lies ventrad
of the scrotal sac. It projects caudad. It is covered by the integument,
which projects at its end as a free fold, the =prepuce=. Within the
prepuce is the projecting =glans penis= (Fig. 113, 7). It is conical and
bears on the ventral side of its free end the opening of the =urethra=,
the common urinogenital opening. On the side on which the urethra opens
the glans is connected to the prepuce by a fold of integument, the
=frenulum=. The surface of the glans is covered with sharp, recurved,
horny papillæ.

_The Scrotum and Testes, and the Ducts of the Testes._--The scrotum
contains the two =testes=, one in each of its compartments. Each testis
lies in a diverticulum of the abdominal cavity, which is lined by an
extension of the peritoneum. The testis has the same relation to this
peritoneal diverticulum that the intestine has to the abdominal cavity;
i.e., it does not lie within the cavity of the diverticulum, but is
suspended apparently within it by means of a fold of its wall which acts
as a mesentery. The peritoneal diverticulum is called the =tunica
vaginalis propria= and consists thus of a =parietal= layer and a
=visceral= layer.

The =tunica vaginalis propria= consists of a slender proximal part
through which the blood-vessels pass to the testis and the vas deferens
from it, and of an expanded distal part in which lies the testis. Only
the distal part lies within the scrotum. The blood-vessels and vas
deferens are suspended in the narrow part of the tunica vaginalis
propria by means of a mesenterial fold similar to that which suspends
the testis, and continuous with it. This fold and the blood-vessels and
vas deferens contained within it form the =spermatic cord= (Fig. 111,
_d_) which passes from the abdomen to the scrotal sac in the narrow part
of the tunica vaginalis propria. In the formation of the human tunica
vaginalis the various layers of the body wall are carried out by it and
form the tunics, or coats of the testis. The one of these coats next the
tunica vaginalis propria (which is reckoned as one of the coats) is the
=tunica vaginalis communis= (or =fascia propria=) and is formed by the
transversalis fascia. Outside of the tunica vaginalis communis is the
=cremaster muscle=, an incomplete layer formed from the fibres of the
internal oblique muscle. Next is the =cremasteric= (or =intercolumnar=)
fascia from the aponeurosis of the external oblique muscle, and outside
of this is the integument forming the scrotum. In this integument there
is a layer of smooth muscle which is sometimes described as the =tunica
dartos=. In the cat the tunica dartos and the cremaster muscle are
wanting. The cremaster is replaced by the elevator scroti muscle. The
coats of the testis are thus five, as follows:

1. The =scrotum= (the integument).

2. =Cremasteric fascia= (subcutaneous fascia).

3. The =levator scroti muscle= (subcutaneous muscle-layer) (Fig. 113,
_j_).

4. =Tunica vaginalis communis= (transversalis fascia).

5. =Tunica vaginalis propria= (peritoneum).

The tunica vaginalis communis is inseparably united with the parietal
layer of the tunica vaginalis propria. Where the spermatic cord passes
from the abdominal wall to the scrotum it is covered by integument and
cremasteric fascia on its ventral surface only, but is entirely
surrounded by the tunica vaginalis propria and tunica vaginalis
communis. The canal by which the spermatic cord passes through the body
wall is known as the =inguinal canal=. The end by which it opens into
the abdominal cavity is the =internal inguinal ring=, and the opposite
end is called the =external inguinal ring=.

The =internal inguinal ring= is merely the point of connection between
the proximal tubular portion of the tunica vaginalis propria and the
abdominal cavity. It is circular, and is situated close against the
lateral side of the lateral ligament of the bladder at its middle.

The =external inguinal ring= is an oval opening in the aponeurosis of
insertion of the external oblique muscle. The aponeurosis of this muscle
ends caudally in a free border along the cranial edge of the pubis, from
the ilium to the pubic tubercle. The external ring is just craniad of
the end of this aponeurosis.

The =inguinal canal= between these rings lies along the lateral border
of the rectus muscle. It is one to one and a half centimeters long. Its
medial wall rests on the rectus muscle; its dorsal wall on the fat
contained within the lateral ligament of the bladder. The lateral and
ventral walls lie on the transversus muscle proximally, on the internal
oblique near the distal end. The wall itself is composed of tunica
vaginalis propria and communis. As it passes within the caudal border of
the internal oblique muscle it receives some aponeurotic fibres from it.
A thin aponeurosis is also continued from the border of the external
ring onto the tunica vaginalis propria.

  [Illustration: FIG. 110.--TESTIS.

  _a_, testis; _b_, caput epididymis; _c_, epididymis; _d_, cauda
  epididymis; _e_, vas deferens; _f_, spermatic cord.]

The =testes= (Fig. 110) are the organs which produce the spermatozoa.
They lie one in each compartment of the scrotal sac, enveloped in the
membranes or tunics described when treating of the scrotum. Each is
attached to the dorsal wall of its peritoneal pouch by a mesenteric
fold. The testis is surrounded by the visceral layer of the tunica
vaginalis propria, and within this, by a dense fibrous covering, =the
tunica albuginea=, which sends septa into its interior. Within the
fibrous covering it is made up of numerous coils of seminiferous tubules
which are readily seen by the naked eye.

The =epididymis= (Fig. 110, _c_) is the beginning of the efferent duct
of the testis. It appears as a flat band with a broad rounded end which
lies on the medial surface of the testis at its cranial end (_b_). From
this point it passes about the cranial end of the testis from its medial
to its lateral surface, forming thus a semicircle with the convexity
ventrad. Thence it passes as a narrower band (_c_) along the dorsal
side of the testis, laterad of the suspending mesentery, to the caudal
end of the testis (_d_). At the caudal end of the testis it is enlarged,
passes from its lateral to its medial surface, and turns at the same
time craniad to become continuous with the vas deferens (_e_).

The enlarged cranial end is the =caput epididymis= (_b_); the enlarged
caudal end the =cauda epididymis= (_d_). The whole epididymis is encased
in a tough fibrous covering similar to that of the testis. The fibrous
covering (albuginea) of the testis and that of the epididymis are
connected by fibrous tissue. Within the fibrous covering the head of the
epididymis is made up of tubules which pass from the testis into its
end: these are the =vasa efferentia testis=. The vasa efferentia unite
within the caput into a single vessel which passes in a very tortuous
course to the cauda. Its numerous windings form the cauda, from the end
of which it passes craniad as the =vas deferens= (_e_).

The =vas deferens= (Fig. 110, _e_; Fig. 111, _c_) is a slender tube much
convoluted at its beginning. It passes from the cauda epididymis (_d_)
along the mesenterial fold of the testis on its medial side, to the
spermatic cord (Fig. 111, _d_). It leaves the spermatic cord at the
internal inguinal ring and, curving over the ureter (Fig. 111, _b_),
bends craniad and approaches the vas deferens of the opposite side
dorsad of the neck of the bladder (Fig. 111, _f_). The two vasa
deferentia pass caudad together as far as the cranial border of the
pubis. There they enter the prostate gland (_g_), pierce the dorsal wall
of the neck of the bladder, and open close together on the inner
surface. The two openings are separated by a slight elevation, the =veru
montanum=.

_The Urethra_ (Fig. 111, _h_).--The urethra is the common urinogenital
duct which is formed by the union of the neck of the bladder (_f_) and
the vasa deferentia (_c_) dorsad of the cranial border of the pubis. It
extends thence to the end of the penis. It is divided into three
portions.

1. The =prostate= portion is the commencement of the urethra; it is
surrounded by the prostate gland (_g_).

2. The =membranous= portion (_h_) extends from the prostate portion to a
point between the crura of the penis. This portion is surrounded by the
thick compressor urethræ muscle, so that its wall appears much thicker
than it really is.

3. The =spongy= portion (pars cavernosa) extends along the ventral side
of the penis to its end in the groove between the corpora cavernosa
penis. At its beginning is an enlargement formed by the bulbocavernosus
muscle. This is known as the =bulbus urethræ=. The walls of the spongy
portion are thick and vascular and form the =corpus cavernosum urethræ=
or =corpus spongiosum=. At its end the corpus cavernosum urethræ is
greatly enlarged and forms the glans penis (_m_).

GLANDS OF THE URETHRA.--1. The =prostate= (Fig. 111, _g_) is a bilobed
gland lying on the dorsal wall of the urethra and surrounding the ends
of the vasa deferentia (_c_). It opens into the urethra at its beginning
by numerous small ducts visible to the naked eye on the inner surface of
the urethra.

2. The =bulbourethral= or =Cowper’s glands= (Fig. 111, _i_).--There are
two bulbourethral or Cowper’s glands, one on either side of the bulbus
of the urethra between the ischiocavernosus and bulbocavernosus muscles.
Each has a covering of muscle-fibres derived from the neighboring
bulbocavernosus (Fig. 113, _l_). Each is said to open by a single duct
into the urethra at the root of the penis.

  [Illustration: FIG. 111.--MALE GENITAL ORGANS.

  _a_, bladder; _b_, _b′_, ureters; _c_, vasa deferentia; _d_, spermatic
  cord; _e_, spermatic artery and vein; _f_, neck of bladder; _g_,
  prostate gland; _h_, urethra; _i_, bulbourethral (or Cowper’s) gland;
  _j_, corpus cavernosum penis, cut from ischium; _k_, ischiocavernosus
  muscle (cut); _l_, penis; _m_, glans penis; _n_, testis.]

_The penis_ (Fig. 111, _l_; Fig. 113, 6) is a cylindrical organ with the
apex directed backward. It is covered by integument which projects at
its free end in the form of a fold, the =prepuce= (Fig. 113), which
ensheaths the glans (Fig. 113, 7) of the penis. Beneath the integument
is a layer of strong fibrous subcutaneous fascia continuous with that of
the surrounding parts. On the dorsum of the penis a thin band of fibrous
tissue, the =ligamentum suspensorium penis=, is continued from the
middle line beneath the pelvic symphysis. This band divides distally,
and its halves ensheath the glans and thus form a support of the penis.

The penis is formed by three bodies, the two =corpora cavernosa penis=
and the single =corpus cavernosum urethræ= (corpus spongiosum).

The =corpora cavernosa penis= (Fig. 111, _j_). Each is a cylindrical
sheath of dense fibrous tissue within which are trabeculæ separating
blood-sinuses. Each corpus cavernosum is attached by the one pointed end
to the caudal border of the ramus of the ischium near the symphysis.
From their attachments the corpora cavernosa approach one another,
forming the =crura= of the penis. They become closely united by their
medial surfaces and pass thus to the free end of the penis where their
somewhat pointed distal ends are imbedded in the glans (_m_). A groove
is left between the corpora cavernosa on the dorsum of the penis, and
there is a second groove on the ventral side. In the latter groove lies
the urethra.

The =corpus cavernosum urethræ= is the spongy portion of the urethra
which lies in the groove on the ventral surface of the penis, between
the corpora cavernosa penis. It becomes greatly enlarged at the distal
end of the penis, forming the =glans= (_m_). A small bone (=os penis=)
is imbedded in the distal end of the penis.


B. FEMALE GENITAL ORGANS (Fig. 112).--The urinal organs of the female
are like those of the male. The neck (_k_) of the bladder is, however,
much longer, extending almost to the border of the ischiatic ramus. The
urethra is consequently short.

The genital organs consist of the =ovaries= (_c_) (the organs which
produce the eggs), the =oviducts= or =uterine tubes= (_e_) (=Fallopian
tubes=), which receive the eggs from the ovaries; a bifid =uterus= (_f_
and _i_) in which the ova undergo their development, and a =vagina=
(_m_) which leads from the uterus to its junction with the neck of the
bladder.

The neck of the bladder (_k_) unites with the vagina to form the
=urogenital sinus= (_n_) which is very short, leads to the external
opening, and is comparable to the male urethra. Ventrad of the external
orifice of the urogenital sinus is the =clitoris=, a rudimentary
structure homologous with the penis of the male.

_The Ovaries_ (_c_).--The ovaries lie in the abdominal cavity in the
same longitudinal line with the kidneys and a short distance caudad of
them. Each is an ovoid body about one centimeter long and one-third to
one-half as broad. On its surface are numerous whitish projecting
vesicles, the larger of which show clear centres. They are the =Graafian
follicles= (best seen in section), which contain the eggs. There may be
present one or more elevations of the size of the largest Graafian
follicles, but of a bright red or brown color. They are the =corpora
lutea= (sing. corpus luteum),--Graafian follicles from which the eggs
have been discharged.

The ovary is held in position by the =broad ligament= of the uterus, a
fold of the peritoneum, which passes here from the uterine tube to the
adjacent body wall. The ovary lies in a sort of a pocket formed by the
broad ligament. In the natural position the pocket opens ventrolaterad.
The ovary is further held in position by the ligament of the ovary
(=ligamentum ovarii=), a short thick cord which passes from the ventral
face of the ovary at its uterine end to the adjacent ventral surface of
the uterus.

_The Uterine Tubes_ (_e_).--The uterine (or Fallopian) tubes or oviducts
are the tubes which convey the ova from the ovary (_c_) to the uterus
(_f_). Each begins with an expanded trumpet-shaped opening, the =ostium
tubæ abdominale= (_d_). Its walls are thin, and the mucosa of its inner
surface is thrown up into undulating, radiating ridges.

The ostium (_d_) lies on the lateral side of the ovary (_c_) at its
cranial end, and the trumpet partly clasps the ovary. From the ostium
the tube (_e_) turns craniad, then mediad, and then caudad, so as to
describe a curve about the cranial end of the ovary. It then extends
caudad on the mediodorsal aspect of the ovary to its junction with the
uterine cornu (_f_). It is sinuous throughout its course, and the first
two-thirds (the =vestibulum=) is of considerably greater diameter than
the last third. Throughout the last two-thirds of its course it lies in
the free border of the broad ligament. Its mucosa is thrown into
irregular folds, mostly longitudinal, and is lined by ciliated
epithelium. From the foregoing description it is seen that the ova must
pass through the body cavity in order to reach the ostium tubæ.

  [Illustration: FIG. 112.--FEMALE UROGENITAL ORGANS, OBLIQUELY VENTRAL
  VIEW.

  _a_, kidney; _b_, ureter; _c_, ovary; _d_, ostium tubæ abdominale;
  _e_, uterine (Fallopian) tube; _f_, cornua of the uterus; _g_, cranial
  edge of broad ligament; _h_, round ligament of the uterus; _i_, body
  of the uterus; _j_, bladder; _k_, neck of the bladder; _l_, position
  of cervix uteri; _m_, vagina; _n_, urogenital sinus or vestibule, with
  M. urethralis; _o_, corpus cavernosum clitoridis, with M.
  ischiocavernosus (cut); _p_, fibres of M. constrictor vestibuli. 1,
  aorta; 2, internal spermatic arteries; 3, uterine arteries; 4,
  external iliac arteries; 5, hypogastric arteries; 6, umbilical artery;
  7, inferior hemorrhoidal artery; 8, branches of N. pudendus.]

_The Uterus_ (_f_, _i_).--The =uterus= consists of a median portion or
=body= (_i_) which is unpaired, and of two =horns= or =cornua= (_f_)
which extend from the body to the uterine tubes. The body (_i_) of the
uterus is a tube about four centimeters long which lies in the abdominal
cavity, ventrad of the rectum and between it and the bladder. Its caudal
end is at the level of the cranial border of the pubis. The cranial end
of its cavity is divided by a median dorsoventral partition into lateral
halves, while the cavity of its caudal portion is unpaired. The mucosa
is thrown up into large longitudinal folds. At its caudal end the uterus
projects into the vagina (_m_), so that when the vagina is opened the
end of the uterus is seen projecting into it as a prominent papilla. The
portion of the uterus thus enclosed by the vagina is the =cervix uteri=
or =neck= of the uterus. Its free end is directed ventrocaudad, and a
prominent ridge is continued from its caudodorsal side along the
mid-dorsal wall of the vagina. The uterine cavity communicates with the
vaginal cavity by a V-shaped opening, the =os uteri=, which looks
ventrocaudad and has its apex directed cranioventrad. Each horn (_f_) of
the uterus passes craniolaterad in a nearly straight course from the
body (_i_) to the uterine tube (_e_). It narrows rapidly and becomes
continuous with the tube. The mucosa is thrown into longitudinal folds.

_Ligaments of the Uterus._--=The Broad Ligament.=--The uterus is held in
place principally by the broad ligaments. These are two folds of the
peritoneum, each of which is attached to the whole length of one of the
cornua and the adjacent part of the uterine tube and to the
corresponding lateral surface of the body of the uterus. Each ligament
ends craniad in a concave free border. Its attached border forms a
curved line which begins laterad of the kidney and extends thence to the
lateral ligament of the bladder. From the lateral ligament of the
bladder the broad ligament extends caudad into the =rectovesical= pouch
of the peritoneum, which lies between the rectum and the bladder. It
holds the body of the uterus to the lateral wall of this pouch, and
together with the opposite ligament and the body of the uterus forms
thus a transverse partition, which divides the rectovesical pouch into
dorsal and ventral portions.

The =round ligament= (_h_) is a fibrous band which extends from a point
of the body wall, which corresponds exactly to the internal inguinal
ring of the male, to the cornu of the uterus about two centimeters from
the cranial end. It is attached to the broad ligament by an intervening
fold of peritoneum.

_The Vagina_ (_m_).--The =vagina= extends from the os uteri (at _l_)
dorsad of the symphysis of the pelvis to a point a short distance
craniad of the caudal border of the ischiatic symphysis. At this point
it joins the neck of the bladder (_k_) to form the =vestibulum= or
=urogenital sinus= (_n_), which is homologous with the urethra of the
male.

_Urogenital Sinus_ (_n_).--The =urogenital sinus= extends from the
caudal end of the vagina (_m_) to the external opening, which is
situated ventrad of the anal opening. It is about a centimeter long and
nearly as wide, and is marked off from the vagina by a circular fold of
mucosa, while its inner surface presents longitudinal folds. On its
ventral wall at its cranial end is the opening of the neck of the
bladder, which is enclosed by a ring-like elevation of the mucosa, most
prominent at the sides. The external entrance to the urogenital sinus
forms the =vulva=.

_The Clitoris._--The =clitoris= is a minute organ homologous with the
penis and lying on the ventral floor of the urogenital sinus. Its distal
end lies at the entrance of the urogenital sinus on its ventral border.
In adult specimens the =prepuce= of the clitoris appears as a slight
elevation of the integument surrounding a central vascular structure
which appears red in the fresh organ. From the clitoris there are two
small =corpora cavernosa clitoridis= (_o_) passing craniad and then
diverging to be attached to the ischiatic rami. The ischiatic portion of
each is covered by a muscle (ischiocavernosus). The clitoris is said to
contain a bone.

=Mammary Glands.=--The mammary glands secrete the milk, and lie on the
ventral surface of the body beneath the integument. The separate glands
are closely gathered into two chief masses, one on each side the ventral
middle line. Each of these extends from about the region of the fourth
rib to the caudal end of the abdomen, ending over the pubic symphysis.
On each side the glands are gathered into five groups, each of which is
furnished with a =nipple=. The nipple is a projection of the integument,
having near its distal end numerous fine openings for the ducts of the
glands. The first two nipples are on the thorax, the other three on the
abdomen, the most caudal ones being about two or three centimeters in
front of the cranial edge of the pubis.

Rudimentary mammary glands and nipples are present in the male.


MUSCLES OF THE UROGENITAL ORGANS, RECTUM, AND ANUS (Figs. 113 and
114).--The muscles connected with the caudal openings of the alimentary
canal and of the urogenital organs are closely interrelated, a single
muscle sometimes acting on parts of both systems. For this reason all
these muscles are described together.

The region lying between the anus and the external opening of the
urogenital organs is known as the =perineum=. The perineum is formed
chiefly by muscles and fascia.


_a. Muscles common to the Male and Female._--=M. sphincter ani externus=
(Fig. 113, _i_; Fig. 114, _a_).--This muscle is confounded with the
levator scroti (Fig. 113, _j_) or the levator vulvæ (Fig. 114, _b_). The
two take origin in common from the integument on the dorsum of the root
of the tail dorsad of the fifth caudal vertebra. There the fibres from
the opposite sides are intermingled. The common muscle passes ventrad
about the tail as a flat band close to the integument. Dorsad of the
anus the inner fibres of the muscles of the opposite sides are united.
They then separate and surround the anus as a band five millimeters wide
situated beneath the integument. Ventrad of the anus the fibres are
again intermingled. Some fibres on each side then continue to the
scrotum as the levator scroti (Fig. 113, _j_) or to the vulva as the
levator vulvæ (Fig. 114, _b_). Fibres also pass onto the anal pouch and
unite with the sphincter ani internus, forming the =constrictors of the
anal pouch= (Strauss-Durckheim).

=M. sphincter ani internus= (Fig. 113, _h_; Fig. 114, _c_).--The
sphincter ani internus is a broad and thick band of striated
muscle-fibres which surrounds the rectum at the anus. Dorsad the band is
about two centimeters broad, while ventrad it is less than one. In the
ventral median line some of the fibres pass craniad to help in forming
the bulbocavernosus muscle. The muscle surrounds the anal sac.

(The muscle here described under this name is that described under the
same name in the cat by Strauss-Durckheim and Mivart; it corresponds,
however, to a part of the sphincter ani externus of the dog, as
described by Ellenberger and Baum.)

=M. levator ani= (or =pubiocaudalis=) (Fig. 162, 11).--This muscle lies
in the pelvic cavity. Each muscle forms a nearly vertical sheet, and
between the two are the rectum and the urethra.

_Origin_ from the symphysis of the pelvis.

_Insertion_ into the midventral line of the centra of the third, fourth,
and fifth caudal vertebræ, close to the muscle of the opposite side.
This muscle is frequently continuous with the iliocaudalis (Fig. 162,
11′).

_Action._--Bends the tail and compresses the rectum.

=M. ischiocavernosus= (Fig. 113, _m_; Fig. 114, _e_).--A small, flat,
spindle-shaped muscle which lies upon the crus of the penis or clitoris.
Each has

_Origin_ from the caudal border of the ramus of the ischium, about one
centimeter from the median line.

_Insertion_, in the male, into the whole outer surface of the crus
penis, or bulb of the corpus cavernosum penis. In the female the muscle
is smaller than in the male, and the insertion is into the ventral
surface of the urogenital sinus, at the base of the clitoris.

=M. transversus perinei= (Fig. 114, _i_).--A small bundle of fibres
which arises from the medial surface of the ischium, just dorsad of the
origin of the ischiocavernosus, and passes mediad to join the sphincter
ani internus (_c_).

=M. caudoanalis= (S.-D.) (Fig. 113, _f_; Fig. 114, _g_).--A slender,
flat bundle of fibres having origin on the middle line of the ventral
surface of the second and third caudal vertebræ. It passes caudoventrad,
lying between the levator ani and the caudorectal (Fig. 113, _e_; Fig.
114, _j_), and unites with the ventral portion of the sphincter ani
internus (Fig. 113, _h_).

_Action._--Draws the anus craniodorsad.

  [Illustration: FIG. 113.--MUSCLES OF THE ANUS, UROGENITAL ORGANS, AND
  TAIL IN THE MALE (SLIGHTLY SCHEMATIC).

  One side of the pelvis has been removed, _a_, _a′_, M. extensor caudæ
  lateralis; _b_, M. abductor caudæ externus; _c_, _c′_, M. flexor caudæ
  longus; _d_, M. flexor caudæ brevis; _e_, M. caudorectalis; _f_, M.
  caudoanalis; _g_, M. caudocavernosus; _h_, M. sphincter ani internus;
  _i_, M. sphincter ani externus; _j_, M. levator scroti; _k_, M.
  rectocavernosus; _l_, M. bulbocavernosus; _m_, M. ischiocavernosus
  (cut); _n_, M. compressor urethræ membranaceæ. 1, tail; 2, rectum; 3,
  bulbourethral or Cowper’s gland; 4, prostate gland; 5, symphysis
  pubis; 6, penis; 7, glans penis; 8, testis; 9, spermatic cord.]

=M. caudorectalis= (Fig. 113, _e_; Fig. 114, _j_).

_Origin_ from the ventral surface of the sixth and seventh caudal
vertebræ. A small, at first unpaired band two or three millimeters wide
is formed, which passes cranioventrad, soon dividing into two lateral
halves. These spread out over the sides of the rectum, forming a broad
sheet of fibres which pass into the walls of the rectum, among the
transverse fibres of the latter. This muscle is covered by the
caudoanalis (Fig. 113, _f_), caudocavernosus (_g_) (or caudovaginalis,
Fig. 114, _h_), iliocaudalis, and levator ani.


_b. Muscles Peculiar to the Male_ (Fig. 113).--=M. levator scroti=
(_j_).--This is a band of fibres which passes ventrad in the median line
from the sphincter ani externus (_i_) onto the scrotum. Here it spreads
out beneath the skin, forming especially a well-marked bundle in the
median furrow between the two testes.

=M. rectocavernosus=, or =retractor penis= (_k_).--A small bundle of
fibres which arises in two parts from the ventral surface of the
sphincter ani internus (_h_). The two parts unite into a single bundle
which passes caudad on the middle line of the ventral surface of the
penis; it is inserted into the corpus cavernosum just proximad of the
glans. The muscle is covered only by integument, and overlies the
ischiocavernosus (_m_).

=M. caudocavernosus= (S.-D.) (_g_).--A slender bundle just craniad of
the caudoanalis (_f_).

_Origin_ on the median ventral line of the first two caudal vertebræ.
The muscle passes caudoventrad, lying between the levator ani and the
caudorectal (_e_). It divides into two bands, one of which is inserted
into the base of the corpus cavernosum, while the other extends farther
caudad and is inserted at the distal extremity of the corpus cavernosum.

_Action._--Flexes the penis (bends it backward).

=M. bulbocavernosus= (=accelerator urinæ=) (_l_).--The two muscles cover
the ventral surface of the penis.

_Origin_ of each from a median raphe, which passes from the bulbous
portion of the urethra toward the anus. The fibres pass toward the
distal end of the penis and have their

_Insertion_ into the distal half of the lateral surface of the corpus
cavernosum penis.

=M. compressor urethræ membranaceæ= (_n_).--A thick layer of striated
muscle-fibres which surrounds the urethra between Cowper’s gland (3) and
the prostate (4). The fibres have a circular course, and the cranial
ones are attached to the crura of the penis. The other fibres have no
fixed attachment.


_c. Muscles Peculiar to the Female_ (Fig. 114).--=M. levator vulvæ=
(Strauss-Durckheim), or =constrictor cunni= (_b_).--This is homologous
with the levator scroti of the male. It consists of a band of fibres
which pass ventrad from the external sphincter ani (_a_) and surround
the vulva (3), lying immediately beneath the integument.

=M. constrictor vestibuli=, or =rectovaginalis= (Strauss-Durckheim)
(_d_).

  [Illustration: FIG. 114.--MUSCLES OF THE ANUS AND UROGENITAL ORGANS IN
  THE FEMALE.

  _a_, M. sphincter ani externus; _b_, M. levator vulvæ; _c_, M.
  sphincter ani internus; _d_, M. constrictor vestibuli; _e_, M.
  ischiocavernosus (cut); _f_, M. urethralis; _g_, M. caudoanalis; _h_,
  M. caudovaginalis; _i_, M. transversus perinei; _j_, M. caudorectalis.
  1, the tail; 2, anus; 3, vulva; 4, rectum; 5, vagina; 6, neck of the
  bladder.]

_Origin_ from the sides of the sphincter ani internus (_c_). The muscle
forms a distinct bundle two or three millimeters wide, which passes
ventrocaudad and is _inserted_ into the ventral surface of the
urogenital sinus, caudad of the insertion of the ischiocavernosus (_e_).

=M. caudovaginalis= (Strauss-Durckheim) (_h_).--A slender band just
craniad of the caudoanalis (_g_), and corresponding to the
caudocavernosus of the male.

_Origin_ from the median line of the ventral surface of the first two
caudal vertebræ. The muscle passes caudoventrad, lying between the
levator ani and the caudorectal (_j_), and is _inserted_ into the
ventral side of the urogenital sinus, at the base of the clitoris.

=M. urethralis= (_f_).--This consists of fibres surrounding the cranial
part of the urogenital sinus and the caudal parts of the vagina and neck
of the bladder.

_Origin_ partly on the caudal part of the symphysis of the ischium,
partly from the ventral surface of the urogenital sinus, where the
fibres are attached to the corpora cavernosa clitoridis. The fibres pass
dorsad over the surface of the sinus, and over the surface of the union
of the vagina and neck of the bladder, to be inserted into the sides of
the vagina and the dorsal surface of the urogenital sinus.



THE CIRCULATORY SYSTEM.


I. THE HEART. COR.

The heart lies in the mediastinum, enclosed in the pericardial sac, and
projects rather more toward the left than toward the right. It is an
ovoid or pear-shaped organ, with its long axis directed approximately
craniocaudad. Its caudal end or apex is, however, directed slightly
ventrad and to the left, while the larger cranial end or base faces
slightly dorsad as well as craniad.

Laterally and dorsally the heart is largely covered by the lungs. The
ventral side and a considerable portion of the lateral surface are,
however, not thus covered, so that they lie against the thoracic wall.
The heart extends from about the fourth or the fifth to the eighth rib,
and its apex touches the diaphragm.

The cavity of the heart is divided by a longitudinal dorsoventral septum
into lateral halves--a right and a left side. Each side is again divided
by a transverse dorsoventral septum (=auriculoventricular=) into two
chambers, one of which, the =auricle=, lies at the base; the other, the
=ventricle=, lies at the apex of the heart. There are thus right and
left auricles and right and left ventricles. An external groove, partly
filled with fat, separates the auricular portion of the heart from the
ventricular part; this groove is known as the =sulcus coronarius=.

Each auricle or ventricle has a single set of blood-vessels either
leaving it or entering it. Thus the blood enters the right auricle by
the =inferior= and =superior= venæ cavæ (Fig. 116, _d_ and _e_) (præcava
and postcava). It passes thence into the right ventricle, and from the
right ventricle to the lungs by a single =pulmonary artery= (Fig. 115,
_f_). It returns to the left auricle by the numerous =pulmonary veins=
(Fig. 116, _g_, _h_, _i_), and passes thence to the left ventricle.
From the left ventricle it passes to the body by a single =aorta= (Fig.
115, _g_).

When the heart is viewed from the ventral surface (Fig. 115), a
considerable blood-vessel, the =coronary artery= (_q_), running from the
base to a point a little to the right of the apex, indicates the
position of the septum (ventricular septum), between the right (_a_) and
left (_b_) ventricles. The apex thus belongs to the left ventricle. From
the cranial end of the right ventricle the pulmonary artery (_f_) is
seen passing obliquely craniad and toward the left. Beneath the
pulmonary artery the aorta (_g_) appears rising from the middle of the
base of the heart and passing directly craniad. At the base appears a
part of the auricular appendage of the left auricle (_d_), and at the
right a part of the right auricular appendage (_c_). The former (_d_) is
larger and bent at right angles, so that its free end is directed toward
the apex.

In the dorsal view (Fig. 116) the position of the ventricular septum is
not indicated. On the surface of the left ventricle a short distance
from the ventricular septum and nearly parallel to it are seen branches
of the coronary artery and the coronary vein passing toward the apex.
Craniad of the left ventricle is seen the left auricle (_b_) with the
pulmonary veins (_g_, _h_, _i_) opening into it. Craniad of the right
ventricle (_a_) is the right auricle (_c_) with the venæ cavæ (_d_ and
_e_) opening into it near the middle. Coming from beneath the auricles
are seen the pulmonary artery (_j_) and the aorta (_f_).

The =chambers of the heart=.

1. The =right auricle= (atrium dextrum) (Figs. 115 and 116, _c_).
Externally the right end of the right auricle projects so as to form its
=auricular appendage= (Fig. 115, _c_) which lies at the right of the
base of the aorta (Fig. 115, _g_). The superior vena cava (Fig. 116,
_e_) is seen entering near the cranial end of the auricular septum
opposite the base of the aorta. The inferior vena cava (Fig. 116, _d_)
enters the auricle near the coronary sinus and close to the auricular
septum. The netted appearance which the wall, especially that of the
appendage, presents externally is due to the muscular thickenings of the
wall (=musculi pectinati=).

  [Illustration: FIG. 115.--HEART, VENTRAL VIEW.

  FIG. 116.--HEART, DORSAL VIEW.

  Fig. 115.--_a_, right ventricle; _b_, left ventricle; _c_, right
  auricular appendage; _d_, left auricular appendage; _e_, conus
  arteriosus; _f_, pulmonary artery; _g_, aortic arch; _h_, thoracic
  aorta; _i_, vena cava superior; _j_, innominate artery; _k_, left
  subclavian artery; _l_, left common carotid; _m_, right common
  carotid; _n_, right subclavian; _o_, azygos vein; _p_, the two
  innominate veins; _q_, coronary artery.

  Fig. 116.--_a_, right ventricle; _b_, left auricle; _c_, right
  auricle; _d_, vena cava inferior; _e_, vena cava superior; _f_, aorta;
  _g_, _h_, _i_, groups of pulmonary veins (_g_, dorsal group; _h_,
  sinistral group; _i_, dextral group); _j_, pulmonary artery (division
  into two); _k_, innominate artery; _l_, left subclavian; _m_, left
  common carotid; _n_, right common carotid; _o_, right subclavian; _p_,
  azygos vein.]

The cavity (including that of the auricular appendage) is somewhat
egg-shaped, with its long axis transverse. The musculi pectinati, which
branch and unite into a network, are most abundant on its dorsal wall at
the right. The axes of the two venæ cavæ if produced into the cavity of
the auricle would meet one another at its centre and nearly at right
angles. Caudad of the opening of the inferior vena cava is seen the
slit-like opening of the =coronary sinus=, guarded craniad by the
semilunar =valve of the coronary sinus= (or valve of Thebesius). The
coronary sinus receives blood from =coronary veins=, which collect it
from the walls of the heart.

In the auricular septum ventrad of the opening of the inferior vena cava
is seen a faintly marked smooth oval depression, the =fossa ovalis=.
When the auricular septum is examined by transmitted light it is seen to
be thinner over the fossa ovalis. There is an opening, =foramen ovale=,
at this point in fœtal life, so that the blood of the inferior vena cava
then passes directly from the right auricle to the left auricle. Caudad
the cavity of the right auricle communicates with that of the ventricle
by the large oval auriculoventricular opening, which is guarded by the
tricuspid valves (Fig. 117).

2. The =right ventricle= (ventriculus dexter) (Figs. 115 and 116, _a_)
does not reach quite to the apex of the heart, so that it makes up less
than one-half of its ventricular portion. It makes a half-spiral turn
about the left ventricle, from its lateral side at the apex toward its
ventral side at the base, where it ends in the pulmonary artery (Fig.
115, _e_). Its wall is very thin as compared with that of the left
ventricle. Its cavity (Fig. 117) is nearly flat on its medial side,
convex on its lateral side. It communicates with the auricle
craniodorsad. Cranioventrad the cavity is narrower and turns around
toward the ventral side of the heart and opens into the pulmonary
artery. That portion of the ventricle between the auriculoventricular
opening and the pulmonary artery is the =conus arteriosus= (Fig. 115,
_e_; Fig. 117, _f_). Internally the wall presents many muscular
=trabeculæ= (Fig. 117, _a_) of various sizes. These are more numerous
over the ventricular wall than on the septum. They do not occur on the
conus (_f_). Surrounding the auriculoventricular opening is the
=tricuspid valve= (Fig. 117, _d_, _d′_, _d″_). It consists of three
flaps. One of these (_d′_) is septal (i.e., it lies against the septum),
while of the two others which do not lie against the septum, one is
dorsal (_d″_) and the other ventral. Each flap is thin, semicircular,
and membranous, and is attached to the border of the auriculoventricular
opening by the diameter of the semicircle. The free border of each is
attached to the wall of the heart by numerous delicate tendinous bands,
the =chordæ tendineæ= (_c_), some of which are attached to the lower
face of each valve. The chordæ tendineæ of the septal valve (or most of
them) are attached at their opposite ends to the septum directly, while
those of the dorsal and ventral flaps are attached to the ends of three
or more band-like muscles, =columnæ= (or trabeculæ) =carneæ= (_b_),
which are fixed by their opposite ends to the ventricular wall.

  [Illustration: FIG. 117.--HEART, WITH RIGHT VENTRICLE LAID OPEN TO
  SHOW THE TRICUSPID VALVE.

  _a_, trabeculæ; _b_, columnæ carneæ; _c_, chordæ tendineæ; _d_, _d′_,
  _d″_, the three flaps of the tricuspid valve; _e_, aorta; _f_, conus
  arteriosus, laid open; _g_, semilunar valves of the pulmonary artery.]

Between the conus arteriosus (_f_) and the pulmonary artery are three
pocket-like =semilunar valves= (Fig. 117, _g_), one ventral, one
dextral, and one sinistral. Between each valve and the wall of the
pulmonary artery there is an enlargement of the cavity of the artery,
one of the =pulmonary sinuses= (or sinuses of Valsalva). Beyond the
sinuses the pulmonary artery divides into right and left branches (Fig.
116, _j_).

3. The =left auricle= (atrium sinistrum) (Fig. 115, _d_; Fig. 116, _b_).
The auricular appendage (Fig. 115, _d_) is bent at right angles and its
apex turned caudad. The cavity is thus irregular. Muscular trabeculæ
occur only in the auricular appendage. When the auricular septum is
examined by transmitted light the position of the fossa ovalis is
indicated at about the middle of the septum as seen from the left side.
Ventrad of it is a fold of the septal wall.

The =pulmonary veins= enter the dorsal wall of the auricle in three
groups (Fig. 116, _g_, _h_, _i_). Each group opens into a more or less
pronounced sinus or extension of the auricular cavity. The sinuses may
be called, on account of their position, dorsal (_g_), sinistral (_i_),
and dextral (_h_).

4. The =left ventricle= (Fig. 115, _b_) occupies rather more than the
left half of the base of the heart. Its walls are two or three times as
thick as those of the right ventricle. Internally its walls present a
few muscular bands, comparable to the trabeculæ of the left ventricle.
There are two very large columnæ carneæ, one dorsad and one ventrad. At
the cranial end it communicates near the lateral wall with the left
auricle by the auriculoventricular opening, and near the septum with the
aorta. The =bicuspid valve= (or mitral valve), which guards the
auriculoventricular opening, consists of two flaps, one septal and one
lateral. Their chordæ tendineæ, which come from their free borders as
well as from their outer surfaces, are attached to the columnæ carneæ,
chordæ passing from both valves to each columna carnea.

The opening into the aorta is guarded by three =aortic semilunar=
valves, each of which partly conceals an =aortic sinus= (or sinus of
Valsalva). One valve is dorsal, one sinistral, and one dextral. In the
dextral sinus is the opening of one of the =coronary arteries=, which
carry blood to the walls of the heart.

=Pericardium.=

The pericardium is a sac enclosing the heart. It lies in the middle
mediastinum, and the two halves of the mediastinal septum with their fat
may be dissected away from it. Its wall is composed of two layers, an
external firm fibrous layer and an internal layer of flattened
epithelial cells similar to the peritoneal epithelium (=serous= layer).
The fibrous layer forms a sac which repeats roughly the form of the
heart. This sac is attached to the aorta at the point of origin of the
subclavian artery, to the pulmonary artery at its bifurcation, and to
the venæ cavæ and pulmonary veins near their entrance into the heart. At
these points it is continuous with the fibrous coats of the vessels
named, and from them it is reflected over the heart, forming a complete
sac enclosing it but not attached to it anywhere. The heart lies within
this sac. The serous layer lines the fibrous sac and gives to the
surface of the heart and fibrous layer a smooth glistening appearance.
It is reflected over the heart. The relation of the heart to it is
much the same as the relation of the intestine to the peritoneal sac.
The serous layer consists therefore of two portions, =parietal=, lining
the sac, and =visceral=, covering the heart. The parietal and visceral
portions are continuous along a line which runs approximately parallel
to the auriculoventricular groove and encloses all the great
blood-vessels. Within this line the heart lies against the fibrous layer
of pericardium and is not covered by the serous layer. The serous layer
is easily dissected free from the heart-wall, but its parietal portion
is closely adherent to the fibrous layer.


II. THE ARTERIES. ARTERIÆ.


1. =A. pulmonalis, the Pulmonary Artery= (Fig. 115, _f_).

The pulmonary artery passes craniodorsad and slightly to the left from
the cranial end of the conus arteriosus. One to one and a half
centimeters from the conus it divides into right and left branches (Fig.
116, _j_). Just before the division the dorsal surface of the pulmonary
artery is connected by the short =ligamentum arteriosum=, or ligamentum
Botalli, with the aorta. This is the remnant of a canal which in fœtal
life forms a free communication between the pulmonary artery and the
aorta; this canal is known as the =ductus Botalli=. The ligament is
almost or quite obliterated in the adult cat.

The left branch of the pulmonary artery passes to the left lung,
crossing ventrad of the thoracic aorta. It then divides into branches
which pass to the lobes of the left lung. The point of division of the
left branch of the pulmonary artery lies craniad of all the lobes of the
lung, so that the lobes of the left lung are said to be all
=hyparterial=, i.e., below (or caudad of) the artery.

The right branch passes under (dorsocaudad of) the aortic arch, and
reaches the right lung at about the junction of the cranial lobe with
the remainder of the lung. The cranial lobe of the right lung is
therefore said to be =eparterial=, since it is craniad of the pulmonary
artery; the other lobes are hyparterial. The right branch divides at its
entrance to the lung and is distributed to its lobes.


2. =Aorta= (Fig. 115, _g_; Fig. 118, _a_).

The aorta is the single great vessel which conveys blood from the left
ventricle. It makes a sharp semicircular curve dorsad (Fig. 118, _a′_)
and to the left, passes caudad at the left side of the vertebral column,
and passes between the crura of the diaphragm to reach the abdominal
cavity. It is divisible into =thoracic aorta= (Fig. 118) and =abdominal
aorta= (Fig. 126).


A. =Thoracic Aorta= (Fig. 118).--The first portion of the thoracic
aorta, curved as above described, is the =aortic arch= (_a′_). It lies
in the thoracic cavity opposite the interval between the third and
fourth or fourth and fifth ribs. It is separated from the vertebral
column on the right by the superior vena cava (_q_), and on the left by
the œsophagus (4). At its beginning it lies a little to the right of the
median plane; but it passes at once to the left side of the vertebral
column.

BRANCHES OF THE THORACIC AORTA.

1. =Aa. coronariæ.=--The coronary arteries are two. They arise from the
aortic sinuses. The left one (Fig. 118, _p_) leaves the aorta on the
left side, passes dorsad of the pulmonary artery, and divides into two
branches, one of which follows the auriculoventricular groove (sulcus
coronarius) to the dorsal side of the heart and sends branches to the
adjacent heart-walls, while the other runs onto the ventricles,
following approximately the ventral border of the ventricular septum.
The _right coronary_ artery passes in the auriculoventricular groove
toward the right and dorsad, and supplies the adjacent walls of the
heart.

2. =A. anonyma= (Fig. 115, _j_; Fig. 118, _b_).--The innominate artery
passes craniad from the convexity of the aortic arch (_a′_). It gives
rise first to a small =mediastinal artery= (_m_) which passes ventrad
into the mediastinum, then to the =left common carotid= (Fig. 115, _l_),
then to the =right common carotid= (Fig. 115, _m_). Sometimes the
carotids are given off from a common trunk. Beyond the right common
carotid the innominate is continued as the =right subclavian= (Fig. 115,
_n_).

  [Illustration: FIG. 118.--VESSELS OF THE THORAX, VIEWED FROM THE LEFT
  SIDE.

  _a_, aorta (_a′_, aortic arch); _b_, innominate artery; _c_, left
  subclavian; _d_, right subclavian; _e_, right common carotid; _f_,
  left common carotid; _g_, costocervical axis; _g′_, vertebral artery;
  _h_, internal mammary artery; _i_, axillary artery; _j_, thyrocervical
  axis; _k_, A. transversa scapulæ; _m_, mediastinal artery; _n_,
  intercostal arteries; _o_, œsophageal arteries; _p_, left coronary
  artery; _q_, superior vena cava; _r_, internal mammary vein; _s_, the
  two innominate veins; _t_, sternal artery; _u_, costocervical vein;
  _v_, vertebral vein; _w_, axillary vein; _x_, vein to clavotrapezius
  and lateral ends of the pectoral muscles; _y_, vein accompanying
  second branch of A. transversa scapulæ; _z_, thyrocervical vein. 1,
  external jugular vein; 2, internal jugular vein; 3, vena cordis magna;
  4, œsophagus; 5, thoracic duct; 6, one of the lymphatic ducts from the
  neck. _I_, first rib (cut); _VIII_, eighth rib (cut); _XII_, twelfth
  rib (cut).]

3. =A. subclavia sinistra= (Fig. 115, _k_; Fig. 118, _c_).--The left
subclavian passes craniad from the convexity of the aortic arch. It
curves about the first rib (Fig. 118, _I_) to enter the armpit, where it
becomes the =axillary artery= (_i_).

4. =Aa. intercostales= (_n_).--The intercostal arteries are given off
from the dorsal side of the aorta. Each passes to an intercostal space
and divides into three branches. One of these passes ventrad along the
caudal margin of the cranial one of the two ribs between which it
extends. Another goes to the deep muscles of the back, and the third
enters the spinal canal through the intervertebral foramen. The arteries
for the first and second (and sometimes the third) intercostal space
usually arise from the subclavian (costocervical axis, Fig. 118, _g_).

5. =Aa. bronchiales.=--The bronchial arteries are two, and arise either
from the aorta opposite the fourth intercostal space or from the fourth
intercostal arteries. They accompany the bronchi to the lungs.

6. =Aa. œsophageæ= (Fig. 118, _o_).--The œsophageal arteries are small
branches of varying origin passing to the œsophagus.

7. =Aa. lumbales.=--The lumbar arteries correspond to the intercostals,
but pass off between the lumbar vertebræ. The obliquity of the diaphragm
throws the origin of one or two pairs of them within the thorax.


A. CAROTIS COMMUNIS. THE COMMON CAROTID ARTERY. (Fig. 115, _l_ and _m_;
Fig. 119, _a_).

The two common carotid arteries arise from the innominate artery in the
manner already described. Each passes craniad along the side of the
trachea. In the thorax (Fig. 118, _f_) the common carotid lies mediad of
the subclavian artery (Fig. 118, _c_) and dorsad of the superior vena
cava (Fig. 118, _q_). In the neck (Fig. 119) the artery lies,
accompanied by the vagus and sympathetic nerves and the internal jugular
vein (_b_), in the space between the longus capitis muscle (7) and the
trachea (14); it is covered ventrally by the sternomastoid and
sternothyroid (2) muscles, lying close to the lateral border of the
latter. Near its origin the common carotid may give rise to the small
=inferior thyroid= artery. It then passes to about the level of the
larynx without giving off branches; here it gives off the =superior
thyroid= (_c_) on the ventral side and one or more muscular branches
(_e_) on the dorsal side. One or two centimeters further craniad it
gives off on the dorsal side the =internal carotid= (_g_) and the
occipital artery (_f_). The main artery now takes the name =external
carotid= (_m_).

  [Illustration: FIG. 119.--COMMON CAROTID ARTERY AND INTERNAL JUGULAR
  VEIN.

  _a_, common carotid artery; _b_, internal jugular vein; _c_, superior
  thyroid artery; _d_, cervicalis ascendens artery; _e_, large muscular
  branches; _f_, occipital artery; _g_, internal carotid; _h_, branch to
  larynx; _i_, lingual artery; _j_, external maxillary; _k_, superior
  labial; _l_, inferior labial; _m_, external carotid; _n_, internal
  maxillary; _o_, posterior auricular; _p_, superficial temporal. 1, M.
  sternohyoideus; 2, M. sternothyreoideus; 3, M. geniohyoideus; 4. M
  genioglossus; 5, M. constrictor pharyngis medius; 6, M. constrictor
  pharyngis inferior; 7, M. longus capitis; 8, M. digastricus; 9, M.
  masseter; 10, M. scalenus; 11, M. levator scapulæ (cut); 12, M.
  levator scapulæ ventralis (cut); 13, M. splenius; 14, trachea.]

Branches of the common carotid:

1. =A. thyreoidea ima.=--The inferior thyroid is a small artery which
arises either from the common carotid near its origin, or from the
innominate before the origin of the carotid. It passes craniad on the
trachea as far as the thyroid gland, giving branches to the trachea and
œsophagus.

2. =A. thyreoidea superior= (_c_).--The superior thyroid leaves the
carotid opposite the thyroid cartilage and passes mediad and caudad,
sending branches to the thyroid gland, and the sternothyroid (2) and
sternohyoid (1) muscles. A small branch, the =superior laryngeal=,
passes to the larynx, and supplies those muscles of the larynx which are
not enclosed by the cartilages.

3. =Rami musculares= (_e_).--One or two branches, usually of
considerable size, leave the common carotid at about the same level as
the superior thyroid and pass to the muscles on the dorsal side of the
neck, the main trunk of the artery passing between the longus capitis
(7) and scalenus muscles (10).

4. =A. occipitalis= (_f_).--The occipital artery arises from the common
carotid at about the same point as the internal carotid. It immediately
sends a large branch dorsad, passing between M. longus capitis (7) and
the vertebral column, to the deep muscles of the neck. The occipital
then crosses the outer surface of the digastric muscle (8) to the back
of the skull, and runs along the lambdoidal crest just beneath the
splenius muscle. It sends a number of branches to the muscles of the
back of the neck; and one of its branches may unite with the vertebral
artery as it lies in the groove on the atlas, or with a branch of the
vertebral.

5. =A. carotis interna= (_g_).--The internal carotid artery is one of
the terminal branches of the common carotid. It is very small. It is
given off near or in common with the occipital artery, passes toward the
cranial end of the tympanic bulla, enters the bulla with the Eustachian
tube, and passes into the skull at the foramen lacerum. Its course is
much convoluted before entering the foramen. Within the skull (Fig. 121,
_g_) it joins the posterior cerebral artery (Fig. 121, _f_) at the side
of the hypophysis.

6. =A. carotis externa= (Fig. 119, _m_).--After giving off the internal
carotid the continuation of the common carotid artery receives the name
=external carotid= (_m_). It passes craniad and laterad between the
digastric (8) and styloglossus muscles, where it gives off cranioventrad
the =lingual artery= (_i_) and a number of small muscular branches; also
sometimes the small =laryngeal= artery. At the dorsolateral border of
the digastric (8) it gives off the =external maxillary= artery (_j_),
and about one centimeter farther craniad the =posterior auricular=
(_o_). It now turns mediad, lying against the cartilaginous auditory
meatus, on its cranial side, and gives off the =superficial temporal=
(_p_). The artery then continues mediad, taking the name =internal
maxillary= (_n_)--so that the internal maxillary artery is to be
considered the terminal branch of the external carotid.

Branches of the external carotid artery (Fig. 119):

_a._ =A. lingualis= (Fig. 119, _i_; Fig. 120, _d_).--The lingual artery
leaves the external carotid near its beginning and passes craniomediad
along the ventral border of the digastric muscle (Fig. 120, 9),
accompanied by the hypoglossal nerve. It gives off numerous small
branches to the hyoid and pharyngeal muscles, then passes dorsad of the
hyoglossus muscle (Fig. 120, 6), where it gives off a branch which
passes transversely across the middle line to communicate with the
artery of the other side. Beneath the hyoglossus the artery turns
craniad and passes into the tongue. Here it runs along the medial border
of the styloglossus to the tip of the tongue, giving off numerous
branches into the substance of this organ.

_b._ =Rami musculares.=--Muscular branches pass to the digastric and to
the hyoid muscles. A small branch (Fig. 119, _h_), which may arise
either from the external carotid or from the common carotid near the
beginning of the external carotid, passes to the larynx and supplies the
thyroarytenoid and lateral cricoarytenoid muscles of the larynx.

_c._ =A. maxillaris externa= (Fig. 119, _j_).--The external maxillary
artery leaves the external carotid (_m_) opposite the angle of the jaw
and at about the dorsal border of the digastric muscle (8). It passes
craniad, lying at first beneath the digastric muscle and sending a
branch to the submaxillary gland. Opposite the caudal border of the
mylohyoid muscle it gives off the =submental= artery, turns dorsad,
emerges from beneath the digastric, and passes along the cranial border
of the masseter onto the face. Here it divides into =superior= (_k_) and
=inferior= (_l_) =labial= branches, which pass along the upper and lower
lips, respectively, giving off numerous branches.

The =submental= artery passes to the symphysis menti between the
digastric and mylohyoid muscles, giving off on its course collateral
branches to the muscles of this region.

_d._ =A. auricularis posterior= (Fig. 119, _o_).--The posterior
auricular leaves the external carotid (_m_) opposite the middle of the
bulla tympani and beneath the submaxillary gland. It passes about the
base of the ear on its caudal and dorsal sides outside of the deep
muscles of the occipital region, but beneath the auricular muscles, and
sends several branches to the muscles of the external ear, passing onto
the caudal surface of the concha. It sends also a large branch mediad
to the muscles of the occiput, especially to the temporal muscle, within
which it ramifies. A large branch (=anterior auricular=, Fig. 131, _u_)
passes from the caudal side of the concha craniodorsad, and appears on
the cranial side of the external ear, running along the cranial margin
of the auditory opening.

_e._ =A. temporalis superficialis= (Fig. 119, _p_; Fig. 120, _h_).--The
superficial temporal artery arises from the external carotid as the
latter lies between the cartilaginous auditory meatus and the caudal
border of the masseter muscle. It passes dorsad and gives off soon after
its origin a muscular branch to the masseter, and an =auricular= branch
which passes distad along the concha auris and ramifies over its cranial
surface. The superficial temporal itself passes onto the surface of the
temporal muscle (Fig. 120, 11), to which it gives numerous branches. It
extends to the caudal angle of the eye (Fig. 131, _s_), where it
divides. One branch passes into the lower eyelid; the larger branch
passes along the dorsal side of the eye, sending a branch into the orbit
and small branches onto the dorsal surface of the nose.

_f._ =A. maxillaris interna= (Fig. 119, _n_; Fig. 120, _i_).--The
internal maxillary artery is the continuation of the external carotid.
It turns caudad at the caudal end of the mandible, then passes craniad,
lying dorsad of the pterygoid muscles (Fig. 120, 10), and against the
medial surface of the mandible. It gives off the =inferior alveolar=
artery (Fig. 120, _j_), then the =middle meningeal= (_k_), and then
continuing mediad divides into three or four branches. The branches
redivide, and the twigs form a complicated plexus, the =carotid plexus=
(Fig. 120, _l_), which surrounds the maxillary division of the fifth
nerve near its exit from the foramen rotundum. One of the larger
branches of the plexus enters the skull through the orbital fissure,
lying beside the hypophysis; it divides in the manner described below.

  [Illustration: FIG. 120.--BRANCHES OF EXTERNAL CAROTID ARTERY.

  _a_, common carotid; _b_, branch to larynx; _c_, internal carotid;
  _d_, lingual; _e_, external carotid; _f_, posterior auricular; _g_,
  external maxillary; _h_, superficial temporal; _i_, internal
  maxillary; _j_, inferior alveolar; _k_, middle meningeal; _l_, carotid
  plexus; _m_, branch to temporal muscle; _n_, ophthalmic; _o_,
  infraorbital; _p_, lesser palatine. 1, M. constrictor pharyngis
  inferior; 2, M. sternothyreoideus; 3, M. sternohyoideus; 4, M.
  thyreohyoideus; 5, M. constrictor pharyngis medius; 6, M. hyoglossus;
  7, M. geniohyoideus; 8, M. genioglossus; 9, M. digastricus; 10, Mm.
  pterygoidei externus and internus (cut); 11, M. temporalis (cut).]

Beyond the carotid plexus a main trunk which may be considered the
continuation of the internal maxillary passes craniad, lying on the
dorsal surface of the external pterygoid muscle; nearly opposite the
molar tooth it divides into the =infraorbital= (Fig. 120, _o_) and the
=sphenopalatine= arteries.

Branches of the internal maxillary artery and of the carotid plexus:

1. =A. alveolaris inferior= (Fig. 120, _j_).--The inferior alveolar (or
inferior dental) artery leaves the inferior maxillary just opposite the
condyloid process of the mandible. It enters the mandibular canal by the
mandibular foramen, along with the nerve of the same name, and traverses
the canal, furnishing branches to the lower teeth. It emerges at the
mental foramen, and its terminal branches are distributed to the chin,
but a branch is continued in the bone beyond the mental foramen and
supplies the incisor and canine teeth of the lower jaw.

2. =A. meningea media= (Fig. 120, _k_).--The middle meningeal is a large
vessel which leaves the internal maxillary at about the same level as
the inferior alveolar. It passes into the foramen ovale and ramifies in
the dura mater. Its branches leave distinct impressions on the inner
surface of the bones of the skull.

3. A large branch (Fig. 121, _h_) from the plexus passes into the
cranial cavity through the orbital fissure and lies within the skull at
the side of the hypophysis. It gives off the following branches:

_a._ A =posterior communicating= branch, very short, which extends
caudad and joins the internal carotid artery (Fig. 121, _g_).

_b._ =A. cerebri media= (Fig. 121, _i_).--The middle cerebral artery
passes dorsad on the side of the cerebral hemisphere along the fissure
of Sylvius and divides into numerous branches which are distributed to
the surface of the cerebrum.

_c._ =A. cerebri anterior= (Fig. 121, _j_) Passes dorsad between the
cerebral hemispheres. Just craniad of the optic chiasma the two anterior
cerebral arteries are united by a small communicating branch, thus
completing the circulus arteriosus or circle of Willis (Fig. 121),
surrounding the hypophysis (see page 292).

4. From the carotid plexus several branches pass, arising either
separately or in common, to the masseter, temporal, and pterygoid
muscles.

5. =A. ophthalmica= (Fig. 120, _n_).--The ophthalmic artery passes from
the carotid plexus to the structures in the orbit. It gives off
numerous branches which supply the muscles of the eyeball, and other
structures of this region. It sends an =ethmoidal= branch into the nasal
cavity through the ethmoidal foramen in the orbital plate of the frontal
bone, then continues distad to emerge from the orbit on the medial side
of the eye; here it anastomoses with branches of the superficial
temporal.

6. =A. palatina minor= (Fig. 120, _p_).--The lesser palatine artery
leaves the internal maxillary distad of the carotid plexus, near the
caudal border of the maxillary bone. It passes ventrocaudad into the
soft palate.

7. =A. sphenopalatina.=--The sphenopalatine is one of the terminal
branches of the internal maxillary; it passes mediad through the
sphenopalatine foramen into the nasal cavity, and divides into numerous
branches which supply the mucous membrane of the nose. It gives off just
before it enters the sphenopalatine foramen the =descending palatine=
(=A. palatina descendens=), which passes into the posterior palatine
canal and emerges on the surface of the hard palate, where it ramifies.

8. =A. infraorbitalis= (Fig. 120, _o_).--The infraorbital artery is a
direct continuation craniad of the internal maxillary. It sends off
numerous small branches to the teeth of the upper jaw, and a rather
large branch which passes to the lower eyelid. It then enters the
infraorbital foramen, at the same time dividing usually into two or
three branches; these emerge from the foramen and supply the parts of
the nose and upper lip adjacent to the foramen (Fig. 131, _r_).


A. SUBCLAVIA. THE SUBCLAVIAN ARTERY.

The =left subclavian= (Fig. 118, _c_) arises from the convexity of the
aortic arch just distad of the origin of the innominate artery, and
about two or three centimeters from the heart. It passes craniad and
slightly to the left, and turns into the left arm just craniad of the
first rib.

The =right subclavian= (Fig. 115, _n_) is a direct continuation of the
innominate, the artery receiving the name subclavian after the right
common carotid is given off, usually at about the level of the second or
third intercostal space.

The subclavian has the following branches: the =vertebral artery= (Fig.
118, _g′_), the =internal mammary= (Fig. 118, _h_), the =costocervical
axis= (Fig. 118, _g_), the =thyrocervical axis= (Fig. 118, _j_). Beyond
the last-named branch it continues into the arm as the =axillary= artery
(Fig. 118, _i_; Fig. 122, _g_).

  [Illustration: FIG. 121.--ARTERIES OF THE VENTRAL SURFACE OF THE
  BRAIN.

  _a_, A. vertebralis; _b_, A. spinalis anterior; _c_, A. basilaris;
  _d_, A. cerebelli inferior posterior; _e_, A. cerebelli anterior; _f_,
  A. cerebri posterior; _g_, cut ends of the two internal carotid
  arteries; _h_, cut ends of branches from the carotid plexus (_g_ and
  _h_ are placed within the circulus arteriosus or circle of Willis);
  _i_, A. cerebri media; _j_, A. cerebri anterior.]

_a._ =A. vertebralis= (Fig. 118, _g_′).--The vertebral artery arises
from the dorsal surface of the subclavian opposite the first rib. It
passes craniad and dorsad at the side of the thoracic portion of the
longus colli muscle, and enters the foramen transversarium of the sixth
cervical vertebra. It passes thence craniad through the foramina
transversaria (which together form the =vertebrarterial canal=) and
gives off at the intervertebral foramina branches to the muscles of the
neck and branches which pass across the ventral surface of the spinal
cord to join A. spinalis anterior. Craniad of the foramen transversarium
of the atlas the vertebral artery turns dorsad in the groove on the
lateral surface of the atlas. Here it gives off a large branch which
passes laterodorsad to the muscles of the neck and may anastomose with a
branch of the occipital artery. The vertebral artery then passes into
the vertebral canal through the atlantal foramen. It passes to the
ventral side of the spinal cord and unites at about the level of the
foramen magnum with the vertebral artery of the opposite side (Fig. 121,
_a_) to form the =basilar artery (A. basilaris)= (Fig. 121, _c_), which
passes craniad along the ventral middle line of the brain. Just before
their union the two vertebral arteries (_a_) give off each a branch
which passes caudomediad. These two branches soon unite in the middle
line, forming the =anterior spinal artery= (=A. spinalis anterior=)
(_b_), which passes caudad the entire length of the spinal cord, lying
on its ventral middle line and receiving many communicating branches
from the vertebral, intercostal, and lumbar arteries.

=A. basilaris= (_c_).--This arises by the union of the two vertebral
arteries in the manner just described. It passes craniad along the
ventral middle line of the medulla and pons, giving numerous small
branches to these structures. A large branch, =A. cerebelli inferior
posterior= (_d_), passes on each side to the caudal surface of the
cerebellum, on which it ramifies. At the cranial margin of the pons the
basilar artery divides. From each division a very large branch passes
on each side across the pedunculi cerebri to the cranial part of the
cerebellum; this is =A. cerebelli anterior= (_e_). Just craniad of this,
arising from nearly the same point, the smaller =A. cerebri posterior=
(_f_) passes laterad to the caudal part of the cerebrum; it is joined by
the internal carotid artery (_g_). The small continuations of the two
halves of =A. basilaris= then pass craniad at the side of the hypophysis
to join the posterior communicating branches from the carotid plexus. As
other branches of the carotid plexus unite across the middle line
craniad of the optic chiasma, an arterial circle is formed on the base
of the brain, surrounding the hypophysis and the optic chiasma. This is
known as the =circulus arteriosus=, or circle of Willis (see page 289).

_b._ =A. mammaria interna= (Fig. 118, _h_).--The internal mammary artery
rises from the ventral surface of the subclavian opposite the first rib,
and passes in the mediastinum ventrocaudad to reach the sternum opposite
the third intercostal space. It sends two or three small branches
craniad to the midventral part of the thoracic wall and then extends
caudad at the side of the sternum. It sends off lateral branches to the
ventral thoracic wall, branches to the mediastinum and pericardium, a
branch to the diaphragm which anastomoses with the phrenic; and finally
it passes out of the thoracic cavity caudad of the last costal
cartilage, extends caudad in a zigzag course at the lateral border of
the rectus muscle and anastomoses with the inferior epigastric artery.

_c._ =Truncus costocervicalis= (Fig. 118, _g_).--The costocervical axis
arises from the subclavian opposite the first rib, passes craniodorsad,
and divides almost at once into two branches. The smaller one of these,
the =superior intercostal= (=A. intercostalis suprema=), passes caudad
and, dividing, supplies the first and second intercostal spaces, and
then passes to the deep muscles of the back. The other branch divides
almost immediately into two. One of these, =A. transversa colli=, passes
laterad in front of the first rib and enters the serratus anterior
muscle. In this it passes dorsad, giving off branches to this muscle and
to the levator scapulæ, till it reaches M. rhomboideus, which it
likewise supplies. The other branch (=A. cervicalis profunda=), which
seems to form a continuation of the main artery, passes directly dorsad
and leaves the thoracic cavity between the heads of the first and second
ribs. Here it passes into the deep muscles of the neck; it can be traced
in the substance of the complexus muscle as far forward as the atlas.

_d._ =Truncus thyrocervicalis= (Fig. 118, _j_).--The thyrocervical axis
(or thyroid axis) arises from the subclavian beneath the first rib, a
short distance distad of the origin of the costocervical axis. It passes
laterocraniad and dorsad, lying on the mediocranial side of the brachial
plexus. A short distance from its origin it gives off a branch, varying
much in size, the =cervicalis ascendens= (Fig. 119, _d_), which passes
craniad on the ventral side of the neck, supplying the sternomastoid,
sternohyoid, the cervical portion of the scalenus, and sometimes other
muscles of the neck region. Other branches pass from the thyroid axis to
the inner surface of the clavotrapezius (Fig. 122, _a_) and to the
ventral end of the pectoral muscles. At the level of the cranial border
of the scapula the artery takes the name =A. transversa scapulæ=, or
=suprascapularis=. This divides into three main branches. The first
branch, sometimes large, sometimes small, passes to the lymphatic gland
in the hollow of the shoulder, and to the adjacent muscles; it supplies
the clavotrapezius, acromiotrapezius, levator scapulæ ventralis,
splenius, occipitoscapularis, and rhomboideus. A second branch passes
between the subscapularis and supraspinatus muscles, dividing into
various branches which supply the muscles named. The third branch
pierces the supraspinatus muscle, just craniad of the acromion process,
and ramifies in that muscle.

_e._ =A. axillaris= (Fig. 122, _g_).--The axillary artery is the
continuation of the subclavian laterad of the first rib. It lies caudad
of the brachial plexus and parallel to it. It sends off the following
branches:

1. =A. thoracica anterior= (Fig. 122, _h_).--The anterior thoracic is a
slender artery which leaves the ventral side of the axillary opposite
the first rib and passes caudomediad, to supply the medial ends of the
pectoral muscles (_g_).

2. =A. thoracica longa= (_p_).--The long thoracic artery is larger than
the preceding, leaves the axillary a short distance laterad of it, and
passes caudad to the middle portions of the pectoral muscles (8) and
continues to the inner surface of the latissimus dorsi.

A short distance beyond the long thoracic the axillary divides into two.
The more cranial one of these is the =subscapular= (_l_); the other is
the =brachial= (_g_′).

3. =A. subscapularis= (_l_).--The subscapular artery passes laterad and
gives off a short distance from its origin the =A. thoracicodorsalis=
(_t_) and =A. circumflexa humeri posterior= (see below); it may also
give rise to the =circumflexa anterior humeri= (_l_′), and to the
=profunda brachii= (_u_); these two branches, however, rise more
frequently from the brachial artery (_g_′) and are described in
connection with it. The subscapular artery then passes through the
triangular interval between the scapular end of the long head of the
triceps, the latissimus dorsi, and the glenoid border of the scapula.
Within this interval it sends muscular branches to the long head of the
triceps, the subscapularis, and the latissimus dorsi. That to the latter
muscle is very large. At the border of the scapula, opposite the
tuberosity of the spine, it turns craniad, passes over the lateral
surface of the infraspinatus muscle, supplying it; crosses the spine,
and sends branches into the supraspinatus fossa in both directions
parallel to the scapular spine. These supply the supraspinatus,
acromiotrapezius, and spinotrapezius, and anastomose with the branches
of the transversa scapulæ. As the subscapularis turns craniad onto the
surface of the infraspinatus it sends dorsad a small branch, the
=circumflexa scapulæ=, which passes in the infraspinatus fossa close to
its glenoid border as far as the glenovertebral angle, supplying the
infraspinatus and latissimus dorsi by lateral branches.

  [Illustration: FIG. 122.--BLOOD-VESSELS AND THE MORE VENTRAL NERVES OF
  THE AXILLA, VENTRAL VIEW.

  The pectoral and clavobrachial muscles have been cut and laid aside,
  their ends being shown; only a part of the nerves are exhibited. 1, M.
  clavobrachialis; 2, cut end of M. pectoralis major; 3, cut end of M.
  pectoralis minor; 4, M. biceps; 5, M. teres major; 6, M.
  epitrochlearis, partly cut and turned back; 7, M. latissimus dorsi,
  partly cut; 8, M. pectoralis minor; 9, M. pectoralis major; 10, short
  portion of caput mediale of M. triceps brachii. _a_, branches of the
  thyrocervical axis to clavobrachial and clavotrapezius muscles; _b_,
  suprascapular nerve; _c_, first subscapular nerve; _d_,
  musculocutaneous nerve; _e_, median nerve; _f_, V. axillaris; _f_′, V.
  brachialis; _g_, A. axillaris; _g_′, A. brachialis; _h_, first
  anterior thoracic nerve, accompanied by the anterior thoracic artery
  and vein; _i_, V. subscapularis; _j_, large muscular branch (to
  subscapular muscle) of the subscapular vein and brachial artery; _l_,
  A. subscapularis; _l_′, A. circumflexa humeri anterior; _m_, radial
  nerve; _n_, ulnar nerve; _o_, medial cutaneous nerve; _p_, A.
  thoracica longa; _q_, _r_, second anterior thoracic nerve; _s_, V.
  longa thoracica; _t_, A. and V. thoracicodorsalis; _u_, A. profunda
  brachii; _v_, branch of brachial artery accompanying medial cutaneous
  nerve; _w_, branch of A. collateralis radialis superior; _x_, A.
  collateralis radialis superior; _y_, V. mediana cubiti; _z_, A.
  collateralis ulnaris.]

=A. thoracicodorsalis= (_t_).--This arises from the subscapular a short
distance from its origin and passes across the teres major to the
latissimus dorsi (7), giving branches to both these muscles and to the
epitrochlearis.

=A. circumflexa humeri posterior.=--The posterior circumflex artery
arises from the A. subscapularis close to the origin of the latter. It
passes between the subscapularis muscle and the teres major, close to
the border of the biceps, then between the lateral and long heads of the
triceps. It gives off a branch to the inner surface of the spinodeltoid
and acromiodeltoid, then passes distad to supply the lateral and long
heads of the triceps.

4. =A. brachialis= (_g_′).--The brachial artery is the continuation of
the axillary (_g_) into the arm beyond the origin of the subscapular
(_l_). It passes along that side of the biceps which lies next to the
humerus. It passes thus, accompanied by the brachial vein (_f_′) and
median and ulnar nerves, through the bicipital arch and afterwards
between the biceps (4) and the intermediate division of the medial head
of the triceps to the supracondyloid foramen of the humerus, through
which it passes with the median nerve to reach the concavity of the
elbow. It gives off the following branches:

_a._ =A. circumflexa humeri anterior= (_l_′).--The anterior circumflex
artery usually leaves the brachial near its origin (but may arise from
the subscapular (_l_) or one of its branches); it passes to the biceps
(4) near the origin of the latter and sends a branch proximad to the
head of the humerus.

_b._ =A. profunda brachii= or superior profunda (_u_).--This arises from
the first part of the brachial or it may come off from one of the
branches of the axillary (e.g., the subscapularis). It passes along with
the radial nerve onto the dorsal side of the humerus and supplies the
triceps muscle. It also sends branches to the epitrochlearis (6) and
latissimus dorsi (7).

_c._ =Rami musculares.=--Muscular branches are given off near the
supracondyloid foramen to the biceps (4), epitrochlearis (6), and
brachialis muscles. A nutrient artery leaves the brachial proximad of
the supracondyloid foramen, either separately or in common with the
muscular branches, and passes into the nutrient foramen at the junction
of the middle and distal thirds of the shaft of the humerus, supplying
the bone.

_d._ =A. collateralis ulnaris= (superior) (or A. anastomotica magna)
(_z_).--This leaves the brachial artery just proximad of the
supracondyloid foramen and passes to the convexity of the elbow,
supplying the structures about the olecranon.

_e._ =A. collateralis radialis superior= (Fig. 130).--This rises from
the axillary artery just proximad of the supracondyloid foramen (Fig.
122, _x_), in company with the vena mediana cubiti (_y_), passes
across the surface of the biceps (4), beneath the pectoantibrachialis,
into the concavity of the elbow. Here it gives branches to the
pectoantibrachialis, clavobrachialis, and extensor muscles of the
forearm. It then passes onto the ventroradial border of the forearm
(Fig. 130) and runs along this border, in company with the vena
cephalica (Fig. 130, _c_) and the superficial radial nerve (_g_), to the
wrist, sending off branches to the integument. At the wrist it turns
onto the dorsum of the hand, passing in a gentle curve to the ulnar side
and distad, and giving off a branch for the space between each pair of
metacarpal bones. These branches (Fig. 130, _e_) (=Aa. digitales
dorsales=) pass distad and anastomose with branches coming from the
palm.

_f._ =A. radialis= (Fig. 123).--Distad of the convexity of the elbow the
brachial artery takes the name =radial artery=. It passes from the
supracondyloid foramen on the medial side of the biceps tendon (1) and
beneath the pronator teres muscle (5), giving off small branches, as far
as the middle of the forearm, where it gives off the ulnar artery (_k_).
It then passes from beneath the pronator teres (5) and lies on the
surface of the fifth part of the flexor profundus (8), covered only by
the fascia and integument. Near the wrist it sends off a branch (_m_)
toward the ulnar side of the arm, which passes into the palm on the
surface of the tendon of the flexor profundus, giving twigs to the
digits and to the pad in the palm. A branch from this may join the
ulnar, and the common trunk thus formed passes into the hand and gives
origin to the branches described under the ulnar artery. The presence
and size of this branch of the radial varies with the size of the ulnar
artery, it being smaller or absent as the ulnar is larger. It is shown
at _m_, Fig. 123. The radial artery (_g_) now turns gradually dorsad and
passes beneath the tendon of the extensor brevis pollicis onto the
dorsum of the hand. It passes over the oblique groove on the dorsal
surface of the base of the second metacarpal beneath the tendon of the
extensor carpi radialis longus and passes between the bases of the
second and third metacarpals into the palm of the hand. Here it passes
to the ulnar side and anastomoses with the ulnar artery to form the
palmar arch.

=Branches of the Radial Artery.=

1. =A. radialis recurrens= (_i_).--The radial recurrent arises in the
concavity of the elbow and sends a branch proximad to the structures in
the concavity; it then continues to the radial side of the forearm at
the elbow, supplying adjacent parts of the brachialis (2), the extensor
carpi radialis, and the extensor communis digitorum.

2. =A. ulnaris recurrens= (_j_).--The ulnar recurrent arises on the
medial side of the tendon of the biceps and supplies structures in the
concavity of the elbow on the ulnar side, also the pronator teres (5)
and proximal ends of the flexor carpi radialis and flexor profundis
digitorum.

3. =Rami musculares.=--Muscular branches are given off along the course
of the artery, to adjacent muscles. A nutrient artery to the radius
leaves the radial artery about two centimeters distad of the
supracondyloid foramen.

4. =Aa interosseæ= (=anterior= (_l_) and =posterior=) are given off
usually separately between the origin of the ulnar artery and the biceps
tendon. Sometimes they arise as a common trunk which soon divides. The
=posterior interosseous artery= passes distad, supplying the flexor
muscles of the forearm. It also sends a branch to the pronator teres.
The =anterior interosseous= (_l_) may arise from the ulnar artery. It
passes dorsad to the interosseous membrane, on which it runs distad;
sends a nutrient branch to the ulna, and then passes to the wrist in the
substance of the pronator quadratus, which it supplies. It sends a
branch to the dorsal surface of the wrist; this ramifies on the carpus,
forming a network of small arteries.

  [Illustration: FIG. 123.--NERVES AND ARTERIES OF THE FOREARM, SEEN
  FROM THE FLEXOR SIDE.

  Mm. palmaris longus, flexor carpi radialis, flexor carpi ulnaris, and
  the third and fourth heads of flexor profundus digitorum have been
  removed; also part of M. pronator teres. 1, biceps; 2, conjoined
  tendon of brachialis and clavobrachialis; 3, short portion of caput
  mediale of triceps brachii; 4, intermediate portion of caput mediale
  of triceps brachii; 5, cut ends of pronator teres; 6, brachioradialis;
  7, extensor carpi radialis longus and brevis; 8, fifth head of flexor
  profundus digitorum; 9, second head of flexor profundus digitorum; 10,
  radial part of flexor sublimis digitorum; 11, common tendon of flexor
  profundus digitorum; 12, first head of flexor profundus digitorum; 13,
  cut origin of flexor carpi ulnaris. _a_, ulnar nerve; _b_, median
  nerve; _c_, dorsal cutaneous branch of the ulnar nerve; _d_, palmar
  branch of ulnar nerve; _e_, deep palmar branch; _f_, superficial
  palmar branch; _g′_, A. brachialis; _g_, A. radialis; _h_, A.
  collateralis ulnaris superior; _i_, A. radialis recurrens; _j_, A.
  ulnaris recurrens; _k_, A. ulnaris; _l_, A. interossea anterior; _m_,
  large branch of A. radialis, joining A. ulnaris.]

5. =A. ulnaris= (_k_).--The ulnar artery passes beneath the second,
third, and fourth parts of the flexor profundus digitorum (but outside
of the origin of the fifth part), to the inner surface of the flexor
carpi ulnaris. It supplies the flexor carpi ulnaris, the flexor
profundus and palmaris longus, and passes on the inner surface of the
flexor carpi ulnaris to the wrist. Near the wrist it sends a branch onto
the side of the forearm, and another to its midventral part, and ends in
a small branch to the wrist on the radial side of the pisiform bone.
This branch anastomoses with the radial to form the palmar arch,
described below.

6. The =palmar arch= (Fig. 124) is formed by the termination of the
radial artery (_a_) in the palm and its junction with the end of the
ulnar (_f_). The radial artery reaches the palm between the bases of the
second and third metacarpals and passes thence toward the ulnar side and
distad, piercing the interosseus muscle of the third digit and lying on
the outer surface of the interossei of the third and fourth digits
beneath the adductors of the second and fifth digits. A small
communicating branch from the radial passes to it between the first and
second metacarpals.

Branches of the palmar arch:

=A. princeps pollicis et indicis= (_c_) leaves the palmar arch near its
radial end and sends a branch onto the ulnar side of the thumb and one
onto the radial side of the index.

The =palmar interosseæ= (_d_) are three in number. They leave the palmar
arch (_b_) and pass distad and dorsad in the intervals between the four
ulnar digits. The radial one passes along the ulnar side of the first
digit, the ulnar one along the radial side of the fifth digit. The
middle one divides and supplies the contiguous sides of the third and
fourth digits. Each of these interosseous arteries sends off muscular
branches (_e_) to the short muscles in the palm, and branches into the
fibrous pad which occupies the palm of the hand. The palmar arch also
sends branches onto the dorsum of the hand at the sides of the fourth
metacarpal. Branches pass from these proximad to the wrist.


B. AORTA ABDOMINALIS. THE ABDOMINAL AORTA.--The abdominal aorta emerges
into the abdomen from between the crura of the diaphragm, at about the
level of the second lumbar vertebra. It passes caudad along the dorsal
middle line, lying to the left of the inferior vena cava. It gives off
=parietal= branches to the body wall, and =visceral= branches to the
viscera, and ventrad of the first sacral vertebra it gives off two
large branches on each side, the =external iliac= (Fig. 126, _k_) and
the =hypogastric= (Fig. 126, _l_)--a very small median vessel, the
=sacralis media= (Fig. 126, _o_), continuing the course of the aorta and
passing into the tail.

The aorta gives off the following branches: =A. cœliaca=; =A.
mesenterica superior=; =Aa. adrenolumbales=; =Aa. renales=; A.
=mesenterica inferior=; =Aa. iliolumbales=; =Aa. lumbales= (seven
pairs); =Aa. iliacæ externæ=; =Aa. hypogastricæ=.

A. =A. cœliaca= (Fig. 125).--The cœliac artery is a large branch which
is given off from the aorta one centimeter or less caudad of the opening
in the diaphragm. It passes directly ventrad about three or four
centimeters, then divides, usually at once, into three branches. The
most cranial of these is the =hepatic= (_d_), the next is the =gastrica
sinistra= (_e_), while the third and largest, seeming to form a
continuation of the cœliac, is the =splenic= (_f_) (=A. lienalis=). The
cœliac artery may give rise also, before its division, to the two
=phrenic= arteries (which, however, usually arise from the
adrenolumbales), and either before or at the point of division to one or
two small =Aa. ventriculi dorsales=, which, however, frequently arise
from the gastrica sinistra.

  [Illustration: FIG. 124.

  THE PALMAR ARCH AND ITS BRANCHES IN THE PALM OF THE HAND.

  The interosseous muscles have been removed, except those of the third
  and fourth digits. 1, M. abductor digiti quinti; 2, 3, Mm. interossei
  of third and fourth digits; 4, M. adductor pollicis; 5, M. flexor
  brevis pollicis. _a_, termination of radial artery; _b_, palmar arch;
  _c_, A. princeps pollicis et indicis; _d_, Aa. interosseæ; _e_,
  muscular branches of the same; _f_, A. ulnaris; _g_, deep palmar
  branch of ulnar nerve.]

Branches of the cœliac artery:

1. =A. hepatica= (_d_).--The hepatic artery passes cranioventrad,
pierces the descending limb of the great omentum and passes craniad to
the liver, lying, together with the portal vein and common bile-duct, in
the ventral boundary of the foramen epiploicum (foramen of Winslow) and
contained, together with the last-named vessels, in a fibrous sheath
called the capsule of Glisson. Just before entering the sheath it gives
off the =gastroduodenalis= (_g_). At its termination the hepatic artery
divides, sending branches to the lobes of the liver and a =cystic=
artery to the gall-bladder.

  [Illustration: FIG. 125.--THE CŒLIAC ARTERY AND ITS BRANCHES.

  _a_, abdominal aorta; _b_, A. cœliaca; _c_, A. mesenterica superior
  (cut); _d_, A. hepatica (cut); _e_, A. gastrica sinistra; _f_, A.
  lienalis; _g_, A. gastroduodenalis (cut from A. hepatica); _h_, A.
  pylorica; _i_, A. gastroepiploica dextra; _j_, A.
  pancreaticoduodenalis superior; _k_, A. pancreaticoduodenalis inferior
  (cut from inferior mesenteric); _l_, A. ventriculi dorsalis. 1,
  spleen; 2, stomach; 3, duodenum; 4, pancreas.]

_a._ =A. gastroduodenalis= (_g_).--This arises from the hepatic
near the pylorus and passes caudad, dividing one or two centimeters
from its origin into three branches, =A. pylorica= (_h_), =A.
pancreaticoduodenalis superior= (_j_), and =A. gastroepiploica dextra=
(_i_). The =pylorica= (_h_) (which may arise directly from the hepatic)
passes to the pylorus, thence along the lesser curvature of the stomach,
dividing into numerous branches and anastomosing with the gastrica
sinistra. The =pancreaticoduodenalis superior= (_j_) passes to the
duodenum, supplying it and the duodenal part of the pancreas and
anastomosing with the pancreaticoduodenalis inferior (_k_). The
=gastroepiploica dextra= (_i_) passes along the greater curvature of the
stomach from the pyloric end and supplies the walls of the stomach,
sending branches also to the ascending limb of the great omentum. These
branches anastomose with the terminal branches of the splenic artery.

2. =A. gastrica sinistra= (_e_).--This arises from the cœliac artery and
passes to the lesser curvature of the stomach, extending along this to
the right. It gives off many branches to the walls of the stomach, and
anastomoses with A. pylorica.

=A. ventriculi dorsalis= (_l_).--One or two small arteries which arise
either from the gastrica sinistra or the cœliac artery, and pass toward
the dorsal part of the greater curvature of the stomach near its cardiac
end.

3. =A. lienalis= (_f_).--The splenic artery is the largest of the
branches of the cœliac axis, of which it appears to be the direct
continuation. It divides into two large branches, one to the cranial
end, the other to the caudal end, of the spleen (1). From the latter a
large branch passes to the pancreas and descending limb of the great
omentum.

B. =A. mesenterica superior= (Fig. 126, _d_).--The superior mesenteric
artery is larger than the cœliac. It supplies the blood to the small
intestines and caudal portion of the pancreas and to the ascending and
transverse colon. It arises from the ventral side of the abdominal aorta
about one centimeter caudad of the cœliac axis and passes caudoventrad,
forming a curve with the convexity dextrad. It gives off the
=pancreaticoduodenalis inferior=, =colica media=, =colica dextra=,
=ileocolica=, and numerous branches to the small intestine.

1. =A. pancreaticoduodenalis inferior= (Fig. 125, _k_).--This passes to
the caudal end of the pancreas and a part of the duodenum, anastomosing
with the pancreaticoduodenalis superior.

2. =A. colica media= is a large branch to the transverse and descending
portions of the large intestine. It divides and sends branches in both
directions which anastomose with the colica dextra and with branches
from the inferior mesenteric arteries.

3. =A. colica dextra.=--A small branch which passes to the ascending and
transverse colon, anastomosing with the colica media and ileocolica. It
is sometimes absent.

4. =A. ileocolica.=--This passes to the cæcum and supplies that
structure, sending branches to the ileocolic valve and the caudal end of
the ileum, and anastomosing with the colica dextra and the intestinal
branches of the superior mesenteric.

5. The superior mesenteric now divides into about sixteen terminal
branches which pass to the small intestine. In many cases these branches
unite near the intestine, forming arches, and from these arches numerous
short branches pass to the intestine.

3. =A. adrenolumbalis= (or =lumboabdominalis=) (Fig. 126, _e_).--This
rises from the aorta, one on each side, about two centimeters caudad of
the superior mesenteric. Each passes laterad onto the dorsal body wall,
supplying the muscles of this region. A large branch passes caudad along
the surface of the muscles dorsad of the kidney and anastomoses with the
iliolumbar artery. From the adrenolumbalis rises usually:

=A. phrenica= (_f_).--The phrenic artery rises either from the cœliac
(_c_) or the adrenolumbalis (_e_) and passes to the diaphragm, near its
dorsal border. In the diaphragm it passes ventrad, lying at the medial
margin of the costal portion of the diaphragm, as far as its sternal
portion, where it unites with the artery of the opposite side. The two
thus form an arch, from which radiating arteries pass off to supply the
diaphragm.

4. =A. renalis= (_g_).--The two renal arteries arise from the sides of
the aorta, usually at about the same point, so that the left passes
caudolaterad and the right craniolaterad (owing to the position of the
kidneys). The artery usually divides just before entering the kidney
(2). It passes dorsad of the vein (_t_). The renal artery sometimes
sends a branch to the suprarenal body (1). It also occasionally gives
origin to the spermatic artery (_h_).

  [Illustration: FIG. 126.--ABDOMINAL BLOOD-VESSELS, VENTRAL VIEW.

  _a_, vena cava inferior; _b_, abdominal aorta; _c_, A. cœliaca (cut);
  _d_, A. mesenterica superior (cut); _e_, A. adrenolumbalis; _f_, A.
  phrenica; _g_, A. renalis; _h_, A. spermatica interna; _i_, A.
  mesenterica inferior (cut); _j_, A. iliolumbalis; _k_, A. iliaca
  externa; _l_, A. hypogastrica; _m_, beginning of A. femoralis; _n_,
  A. umbilicalis; _o_, A. and V. sacralis media (_o_, the artery; _o′_,
  the vein); _p_, A. glutea superior; _q_, A. glutea inferior; _r_, A.
  and V. hemorrhoidalis media; _s_, V. adrenolumbalis; _t_, V. renalis;
  _u_, V. spermatica interna; _v_, V. iliolumbalis; _w_, V. iliaca
  communis; _x_, V. femoralis; _y_, V. and A. profunda femoris; _z_, V.
  hypogastrica. 1, suprarenal body; 2, kidney; 3, ureter; 4, outline
  (broken) of rectum.]

5. =A. spermatica interna= (_h_).--This rises from the aorta on each
side at about the level of the caudal ends of the kidneys, and passes
laterad (or it may arise from the renal). In male specimens the artery
turns caudad, along with the corresponding vein (_u_), and passes to the
inguinal canal. Thence it passes along with the vas deferens and the
vein (forming all together the spermatic cord) to the testes and the
other structures in the scrotum.

In females (Fig. 112, 2, page 265) the artery is larger and passes more
nearly directly laterad, being much convoluted. It passes to the ovary,
being now called the =ovarian artery=. It sends branches into the ovary
(_c_) and to the cranial end of the uterus (_f_); the latter
anastomosing with branches of the uterine artery (3).

6. =A. mesenterica inferior= (Fig. 126, _i_).--The inferior mesenteric
artery has its origin from the aorta at about the level of the last
lumbar vertebra. It passes toward the large intestine, and near it
divides into two branches, the =colica sinistra=, which passes craniad
along the descending colon, anastomosing with the colica media, and the
=superior hemorrhoidal=, which passes caudad along the descending colon
and rectum and anastomoses with the middle hemorrhoidal (page 308).

7. =A. iliolumbalis= (Fig. 126, _j_).--The iliolumbar arteries arise
from the aorta about two centimeters caudad of the inferior mesenteric
and pass laterad over the ventral surface of the psoas minor and
iliopsoas muscles. Each divides into two main branches, one passing
caudad and the other craniad; these supply the muscles of this region.
The cranial branch anastomoses with branches of the adrenolumbalis
(_e_). The caudal branch sends an artery through the abdominal wall to
appear at the cranial edge of the thigh; it passes onto the lateral
surface of M. sartorius and extends here some distance distad.

8. =A. lumbalis.=--There are usually seven pairs of lumbar arteries,
passing almost directly dorsad from the dorsal surface of the aorta; the
first pair arising just craniad of the diaphragm, the last at the same
level as the origin of the external iliac. The two arteries of a pair
usually arise from the aorta one behind the other, or they may arise by
a common trunk. They correspond to the intercostal arteries. They pass
between the centra of the vertebræ and the muscles of the dorsal region,
and send one main branch laterad, the other dorsad; both supply the
dorsal muscles. From the dorsal branch small arteries pass into the
vertebral canal to join the anterior spinal artery.

9. =A. iliaca externa= (Fig. 126, _k_).--The external iliac artery
passes obliquely caudad from the aorta, lying ventrad of the common
iliac vein and against the medial surface of the psoas minor muscle. It
passes onto the ventral surface of this and the iliopsoas and at the
same time reaches the tendon of the abdominal muscles; through a small
opening in this tendon lying ventrocaudad of that for the iliopsoas, it
leaves the abdominal cavity. On its emergence from the abdominal cavity
onto the medial surface of the thigh it receives the name =A. femoralis=
(_m_). The branches of the external iliac artery are described below
(page 309).

10. =A. hypogastrica= (or iliaca interna) (Fig. 126, _l_).--The
hypogastric or internal iliac arteries are given off from the aorta
usually within a centimeter caudad of the external iliac. Each passes
caudolaterad, lying on the medial side of the common iliac vein, and
divides into branches which supply the structures within the pelvis and
the muscles about the pelvic wall. There is much variation in the origin
and relations of the branches of this artery. The following seems to be
a very common arrangement: A very short distance from the origin the
=umbilical= artery (_n_) is given off. The hypogastric artery then
extends two or three centimeters and gives off =A. glutea superior=
(_p_), which passes at once to the pelvic wall. A little farther caudad
the hypogastric divides into the =middle hemorrhoidal= (_r_), to the
rectum, and the =glutea inferior= (_q_), which passes out of the
pelvis.

Branches of the hypogastric artery:

_a._ =A. umbilicalis= (Fig. 126, _n_).--This small artery arises from
the hypogastric about one centimeter from the beginning of the latter,
and passes ventrad to the bladder. Here it divides into two
branches--the =superior vesical= to the sides of the bladder, the
=inferior vesical= to the neck of the bladder and the urethra.

_b._ =A. glutea superior= (Fig. 126, _p_).--This passes dorsolaterad
from the hypogastric and reaches the pelvic wall against the medial
surface of the ilium. Here it divides into two branches. One passes
between the iliopsoas muscle and the ventral border of the ilium to the
medial surface of the gluteus maximus; it gives branches to the gluteus
muscles, the pyriformis, and the rectus femoris. The other branch passes
dorsad of the ilium, sending a branch to the medial surface of the
gluteus medius, and a small branch which joins the lateral sacral artery
and enters thus the sacral canal.

_c._ =A. hemorrhoidalis media= (Fig. 126, _r_).--The middle hemorrhoidal
passes ventrad from the hypogastric, onto the lateral surface of the
rectum. It passes caudad near the ventral side of the rectum as far as
the anus. A short distance from the origin it gives off a branch which
passes almost directly ventrad toward the beginning of the urethra. In
the male this branch is small, sending twigs to the urethra and the
prostate. In the female it is much larger, forming =A. uterina= (Fig.
112, 3, page 265). The uterine artery turns craniad onto the uterus,
which it supplies, passing to the cranial end of the uterine cornu and
anastomosing with the ovarian artery.

The middle hemorrhoidal gives off in the female branches to the vagina
(Fig. 112, _m_) and neck of the bladder (_k_), and a large branch to the
urogenital sinus (_n_); it then supplies the anal glands and other
structures about the anus, and anastomoses with the terminal branches of
the hemorrhoidalis superior. In the male branchlets are given to the
urethra, to the bulbourethral (or Cowper’s) gland, and to the penis. The
=A. dorsalis penis= is a small branch which passes along the median
dorsal groove of the penis to the glans. The middle hemorrhoidal then
supplies the structures about the anus and anastomoses with the superior
hemorrhoidal, as in the female.

_d._ =A. glutea inferior= (Fig. 126, _q_).--This is the terminal portion
of the hypogastric. It passes along with the great sciatic nerve to the
great sciatic notch, and reaches the medial surface of M. pyriformis. It
divides into branches which supply the gluteus and pyriformis muscles,
while a small branch accompanies the great sciatic nerve. A small branch
also passes onto the lateral surface of the tail, extending caudad along
its side.

11. =A. sacralis media= (Fig. 126, _o_).--This is the continuation of
the aorta into the sacral and caudal regions. It extends to near the end
of the tail, lying in the ventral middle line against the sacral and
caudal vertebræ. In the caudal region it passes through the hæmal
arches, covered by the chevron bones. Between the vertebræ it gives off
side branches comparable to the intercostal and lumbar arteries of the
aorta.

Branches of the sacralis media:

_a._ =A. sacralis lateralis.=--Behind the first sacral vertebra a large
branch, the lateral sacral, is given off on each side. This enters the
first anterior sacral foramen, gives a branch to the structures in the
sacral canal, and sends a dorsal branch out through the posterior sacral
foramen to the muscles on the dorsal side of the sacrum.

Similar but smaller branches are given off between the succeeding
vertebræ, sacral and caudal.


_The External Iliac and its Branches._--The origin of the external iliac
(Fig. 126, _k_) is described above (page 307). It gives off the
following branches:

1. =A. profunda femoris= (Fig. 126, _y_).--This is given off just
before the external iliac leaves the abdominal cavity. It passes caudad,
and about one centimeter from its origin it gives off three branches,
sometimes all separately, sometimes two in common. One of these passes
mediad in the lateral ligament of the bladder and ramifies on the
lateral surface of that organ. A second passes through the abdominal
wall and into the fat on the medial surface of the thigh; it sends a
branch caudad toward the external genital organs, while its main trunk
passes distad in the subcutaneous fat almost to the knee. From one of
these two a small branchlet passes in the male to the spermatic cord and
accompanies this to the testis; it represents thus the =external
spermatic artery=. The third branch, =A. epigastrica inferior=, passes
directly to the ventral surface of the rectus abdominis muscle, on which
it passes craniad, sending branches to the muscles of the abdominal
walls. It anastomoses with terminal branches of the internal mammary
artery.

The profunda femoris itself passes between the iliopsoas and the
pectineus muscles, then to the medial surface of the adductor femoris.
It divides into branches which supply the pectineus, adductor longus,
adductor femoris, caudofemoralis, quadratus femoris, semimembranosus,
and semitendinosus.

  [Illustration: FIG. 127.--SUPERFICIAL ARTERIES, VEINS, AND NERVES ON
  THE MEDIAL SIDE OF THE LEG.

  _a_, A. and V. femoralis; _b_, N. femoralis; _c_, A. profunda femoris;
  _d_, A. and V. circumflexa femoris lateralis; _e_, ramus muscularis;
  _f_, A. saphena and V. saphena magna; _g_, N. saphenus; _h_, A. and V.
  articularis genu suprema; _i_, N. tibialis; _j_, plantar branch of A.
  saphena; _k_, dorsal branch of A. saphena. 1, M. sartorius; 2, M.
  tensor fasciæ latæ; 3, M. rectus femoris; 4, M. iliopsoas; 5, M.
  pectineus; 6, M. adductor longus; 7, M. adductor femoris; 8, M.
  semimembranosus; 9, M. gracilis; 10, M. semitendinosus; 11, medial
  head of M. gastrocnemius; 12, M. plantaris; 13, M. flexor longus
  digitorum; 14, M. tibialis anterior; 15, tibia.]

2. =A. femoralis= (Fig. 127).--This is the continuation of the external
iliac onto the medial surface of the thigh. The artery lies in a
triangular depression between the borders of the sartorius (1) and
gracilis (9) muscles. The floor of the depression is formed by the
adductor longus (6), pectineus (5), vastus internus, and rectus femoris
(3) muscles. This triangular depression is known as the =iliopectineal=
fossa, or Scarpa’s triangle; it contains also the femoral vein (_a_) and
saphenous nerve (_g_), which pass along with the artery. The artery
extends distad, and at about the middle of the length of the thigh it
passes, along with the vein and nerve, into a groove between the vastus
medialis and the adductor femoris. This groove is converted into a canal
by the overlying aponeurosis; it is known as =Hunter’s canal= or the
=canalis adductorius=. At the distal end of the adductor femoris the
femoral artery ceases to be superficial and passes between the vastus
medialis and the semimembranosus to the popliteal space; it now receives
the name =A. poplitea=.

Branches of the femoral artery:

_a._ =A. circumflexa femoris lateralis= (Fig. 127, _d_).--The lateral
circumflex arises from the femoral about one centimeter from its
emergence from the abdominal cavity. It passes craniad and laterad and
divides into two main portions. One part passes between the rectus
femoris and vastus medialis, gives branches to these muscles, and sends
an ascending branch to the structures about the hip-joint, and a
descending branch into the vastus medialis muscle. The remainder of the
lateral circumflex passes along the inner (lateral) surface of the
sartorius (1) to the cranial border of the leg, giving branches to the
sartorius (1) and tensor fasciæ latæ (2).

_b._ A large =muscular= branch (_e_) passes caudad (or ventrad) and
distad across the distal end of the adductor femoris (7) and between the
gracilis (9) and semimembranosus, supplying these muscles. Other small
muscular branches may be given off from both sides of the femoral.

_c._ =A. articularis genu suprema= (_h_).--The superior articular artery
arises from the femoral, either in common with the saphenous artery or
separately, a little proximad of the point where the femoral ceases to
be superficial. It passes toward the knee, between the vastus medialis
and semimembranosus, and covered by the sartorius (1), and ramifies over
the medial surface of the knee-joint and in the structures just proximad
of the joint.

_d._ =A. saphena= (_f_).--The saphenous artery frequently takes origin
in common with the superior articular (_h_), but may arise separately at
about the same level. It passes distad across the gracilis (9),
accompanied by the saphenous nerve (_g_) and vein, sends several
branches dorsad (toward the knee), and at about the middle of the lower
leg it divides into two main branches, a =dorsal= branch (_k_), passing
to the dorsum of the foot, and a =plantar= branch (_j_), to the sole of
the foot. The dorsal branch is accompanied by the main saphenous nerve
(_g_) and vein. It sends one or two branches to the medial side of the
ankle-joint, passes then onto the dorsum of the foot, and divides into
four main branches. The medial one passes along the medial side of the
medial digit; the other three pass to the intervals between the digits.
Each divides into two branches which supply the contiguous sides of the
two digits between which the interval lies. The dorsal branch thus
supplies arteries to the sides of all the digits except to the lateral
side of the lateral digit. This is supplied by A. suralis.

The plantar branch (_j_) is larger than the dorsal. It passes distad on
the medial surface of the flexor longus hallucis, accompanied by the
tibial nerve, and across the space between the tendon of Achilles and
the flexor. It gives superficial and deep branches to the structures
about the ankle-joint, and sends inward a branch from the lateral side
(Fig. 128, _d_) which joins the termination of A. tibialis anterior to
form the plantar arch. It then passes distad along the plantar surface
of the foot, nearer its medial border. Beneath the pad in the sole of
the foot it divides into three branches which supply the interosseous
spaces between the three digits.

_e._ =A. poplitea.=--The main trunk of the femoral artery passes between
the vastus medialis and the semimembranosus and then through the distal
portion of the adductor femoris to reach the popliteal space. This is
the space ventrad (or caudad) of the knee, between the biceps femoris on
one side and the semimembranosus on the other. Here the artery receives
the name =A. poplitea=, or popliteal artery. The popliteal artery gives
off a number of large branches as it passes through the popliteal space,
passes between the condyles of the femur and underneath the popliteal
muscle, and finally turns dorsolaterad between the tibia and fibula,
just distad of the head of the fibula. It now receives the name =A.
tibialis anterior= and passes distad along the dorsal (anterior) border
of the fibula.

Branches of the popliteal artery:

1. =A. suralis.=--This is a large branch which passes distad from the
caudal side of the popliteal artery. It sends branches to the biceps and
to the fat in the popliteal space, and passes onto the ventral border of
the lateral head of the gastrocnemius. It sends branches to both heads
of the gastrocnemius and to the popliteus, passes distad onto the
lateral surface of the tendon of Achilles, and may be traced to the
proximal portion of the dorsolateral side of the foot, where it sends
many branches to the integument about the ankle-joint. It then passes
along the lateral side of the foot and supplies the artery on the
lateral side of the fifth digit.

2. =Aa. genu posteriores.=--Several small arteries which pass to the
knee-joint.

3. =Rami musculares.=--Numerous small branches to the muscles about the
popliteal space.

4. =A. tibialis posterior.=--This is the largest branch of the popliteal
artery, which it leaves just before the latter passes beneath the
popliteal muscle. The tibialis posterior passes at first mediad, then
turns distad, passes across the popliteus muscle onto the surface of the
flexor longus hallucis, and ramifies in the substance of this muscle and
its tendon. It gives branches also to the gastrocnemius and soleus. (It
does not pass into the foot as does the corresponding artery in man.)

5. =A. tibialis anterior.=--The anterior tibial artery is the
continuation of the popliteal after its passage through the interosseous
membrane between tibia and fibula to the dorsal side of the lower leg.
Here it passes distad, lying against the interosseous membrane, between
the extensor longus digitorum and the tibialis anterior muscle, or
partly imbedded in the substance of the latter. It passes, lying beneath
the tendons of these muscles, through the transverse ligament proximad
of the malleoli, thus reaching the dorsum of the foot. It extends distad
across the tarsus to the space between the second and third metatarsals,
and through this space to the plantar side of the foot (Fig. 128). Here
it receives one or two small branches (_a_ and _d_) from the plantar
branch of A. saphena (forming with them the =plantar arch= (_c_)), and
passing distad and slightly laterad, divides into three main portions
(_e_). These (=Aa. digitales plantares=) pass to the three intervals
between the digits. The medial one passes along the lateral side of the
second digit; the next divides, sending a branch to the lateral side of
the third digit and the medial side of the fourth; the lateral one
passes along the medial border of the fifth digit. The Aa. digitales
plantares send numerous branches to the interosseous muscles.

  [Illustration: FIG. 128.--DEEP ARTERIES ON THE PLANTAR SURFACE OF THE
  FOOT.

  _a_, medial twig from plantar branch of A. saphena; _b_, A. tibialis
  anterior (or plantaris profunda); _c_, plantar arch; _d_, lateral twig
  from plantar branch of A. saphena; _e_, terminal branches from A.
  tibialis anterior.]

Branches of the tibialis anterior:

_a._ =A. tibialis recurrens.=--Immediately after passing through the
interosseous membrane the anterior tibial sends a small artery proximad
to the knee-joint.

_b._ =Rami musculares.=--Numerous short branches throughout the course
of the artery, to the muscles about it.

_c._ =Ramus superficialis.=--A larger branch leaves the lateral surface
of the artery about one-third the distance from the knee to the ankle
and passes along with the superficial peroneal nerve, at first beneath
M. peroneus longus, then superficially. It passes onto the dorsal
surface of the foot and becomes connected with terminal branches of =A.
saphena=.

_d._ =A. tarsea medialis.=--This arises from the tibialis anterior just
distad of the transverse ligament through which it passes at the ankle,
passes over the medial surface of the astragalus, and is distributed to
the ligaments about the ankle-joint. It anastomoses with the plantar
branch of A. saphena.

_e._ =A. metatarsea.=--The metatarsal artery passes laterad from the
tibialis anterior at the distal boundary of the tarsus, on the dorsal
surface of the foot. It sends branches distad in the intervals between
the third and fourth and the fourth and fifth metatarsals.

The distal branches (Fig. 128) of the tibialis anterior have been
described in the general description of the artery.


THE VEINS. VENÆ.

=Venæ pulmonales. The Pulmonary Veins.=

The pulmonary veins follow in the lungs the course of the bronchi. They
enter the left auricle in three groups (Fig. 116, page 276). The first
of these (_i_) comes from the anterior and middle lobes of the right
side, the second (_h_) from the corresponding lobes of the left side,
and the third (_g_) from the terminal lobes of both sides. Each group is
composed of two or three veins and opens into a sinus or extension of
the auricle. The sinuses are from their position dextral (_i_),
sinistral (_h_), and dorsal (_g_).

=The Veins of the Body.=

The veins of the body may be classified into three main groups: (1) the
veins of the heart; (2) the superior vena cava and its branches; (3) the
inferior vena cava and its branches. The portal system of veins will be
considered with the inferior vena cava.


1. Veins of the Heart.

The veins of the heart consist of one large vein, the =vena cordis
magna=, and a number of small veins.

=Vena cordis magna= (Fig. 118, 3).--This arises as a number of scattered
branches on the surface of both ventricles. These unite to form two main
trunks. One of these, on the ventral side of the heart, marks externally
the septum between the two ventricles. It passes beneath the left
auricular appendage, then turns to the left and passes along the sulcus
coronarius to the dorsal side of the heart. Here it unites with the
second main trunk which ramifies over the surface of the left ventricle.
Arriving at the base of the right auricle it enters this by the coronary
sinus, which lies just beneath the opening of the inferior vena cava.

In addition to the vena cordis magna and its branches there are a number
of small veins, especially in the wall of the right ventricle. These
enter the right auricle by a number of small separate openings along the
sulcus coronarius.


2. =Vena cava superior= (Fig. 129, _b_).

The superior vena cava is the great vein returning the blood from the
head, fore-limb, and cranial part of the trunk. It extends from the
level of the first rib on the right side of the vertebral column to the
right auricle. Its caudal end lies dorsad of the aortic arch. Opposite
the right rib it is formed by the junction of the two innominate veins
(_m_).

Branches of the superior vena cava:

1. =V. azygos= (_d_).--The first branch of the superior vena cava is the
azygos vein, which enters the vena cava on the right side a centimeter
or less craniad of the root of the right lung. It is formed in the
abdominal cavity by the confluence of two or three small veins, which
collect the blood from the muscles of the dorsal wall of the abdomen.
The small median trunk thus formed enters the thoracic cavity between
the crura of the diaphragm and lies on the ventral surface of the centra
of the thoracic vertebræ, slightly to the right of the middle line. The
azygos receives the =intercostal= veins (_n_), which correspond to the
intercostal arteries and have the same course and distribution. In the
caudal part of the thoracic cavity the intercostals enter the azygos
separately, but the intercostals of the cranial intercostal spaces
usually unite two or three together and enter the azygos by one or more
common trunks. The azygos also receives =bronchial= and =œsophageal=
veins, corresponding to the similarly named arteries.

  [Illustration: FIG. 129.--THORACIC BLOOD-VESSELS, FROM THE RIGHT SIDE.

  _a_, aorta; _b_, vena cava superior; _c_, vena cava inferior; _d_, V.
  azygos; _e_, A. subclavia dextra; _f_, A. mammaria interna; _g_, V.
  mammaria interna; _h_, costocervical axis; _i_, united trunk of
  vertebral and costocervical veins; _j_, A. and V. axillaris; _k_, V.
  jugularis externa; _l_, V. jugularis interna; _m_, the two innominate
  veins; _n_, intercostal arteries and veins; _o_, thyrocervical axis.
  1, heart; 2, trachea; 3, œsophagus; _I_-_XI_, cut ends of the first
  eleven ribs.]


2. =V. mammaria interna= (_g_).--The internal mammary veins follow the
corresponding arteries. The two veins unite to form a common trunk
which, after receiving a branch from the cranial part of the sternum,
enters the vena cava opposite the third rib.

3. =Vv. anonymæ= (Fig. 129, _m_; Fig. 115, _p_).--The innominate veins
unite opposite the first intercostal space to form the vena cava
superior. Each extends from the cranial end of the vena cava superior
craniolaterad to a point a short distance craniad of the first rib and
is there formed by the union of the =external jugular= (Fig. 129, _k_)
and =subclavian= (_j_) veins. The innominate vein has the following
branches:

A and B. =Vv. vertebralis= and =costocervicalis= (_i_).--The vertebral
and costocervical veins unite to form a single trunk which enters the
innominate about opposite the first rib. These two veins follow the
corresponding arteries. (Sometimes the vertebral and costocervical veins
enter the innominate separately, and in other cases one or more of the
components of the costocervical veins (e.g., the transversa colli) may
enter the axillary vein. In other cases the entire common trunk of the
vertebralis and costocervicalis may enter the superior vena cava
directly.)

C. =V. subclavia.=--The subclavian vein enters the innominate at about
the level of the first rib. Outside of the thorax it is called the
axillary vein (_j_); this comes from the arm.

  [Illustration: FIG. 130.

  SUPERFICIAL ARTERIES, VEINS, AND NERVES ON THE EXTENSOR SIDE OF THE
  ARM AND DORSUM OF THE HAND.

  _a_, V. cephalica; _b_, V. mediana cubiti; _c_, V. cephalica
  antibrachii; _d_, A. collateralis radialis superior; _e_, Aa. and Vv.
  digitales dorsales; _f_, A. radialis; _g_, superficial radial nerve;
  _h_, N. musculocutaneus; _i_, N. cutaneus medialis.]

=Veins of the Arm.=--The blood is returned from the arm by two systems
of veins,--a deep and a superficial system.

The deep system is composed of veins which correspond to the branches of
the axillary artery, follow in general the same course, and receive the
same names (Fig. 122). They unite to form the axillary vein. The
brachial vein does not pass with the brachial artery through the
supracondyloid foramen.

The superficial system comprises the vena cephalica and its branches.

=V. cephalica= (Fig. 130).--Several superficial branches lying in the
palm of the hand unite to form a common trunk which curves about the
radial side of the wrist and here unites with a similarly formed trunk
from the dorsum of the hand. The vein formed by this union, vena
cephalica (antibrachii) (_c_), passes to the elbow accompanying the
radial nerve (_g_) and the collateral radial artery (_d_), and lying on
the extensor carpi radialis longus muscle just beneath the integument.
It receives small lateral superficial branches. At the elbow it divides
into two: these are the vena cephalica (humeri) (_a_) and the =vena
mediana cubiti= (_b_). The latter passes beneath the pectoantibrachialis
muscle, across the biceps, and unites with the brachial vein in the
concavity of the elbow.

The vena cephalica (humeri) passes at the elbow onto the upper arm,
following the lateral border of the clavobrachial muscle. It thus
reaches the acromiodeltoid muscle, where it divides into two branches.
One passes inward beneath the acromiodeltoid, and joins the vena
circumflexa posterior (a branch of the axillary). The second continues
over the outer surface of the shoulder, and finally joins the vena
transversa scapulæ (a branch of the external jugular).

D. =V. jugularis externa= (Fig. 131; Fig. 65, 5, page 109).--The
external jugular vein comes from the head and face. It is formed by the
junction of the anterior (Fig. 131, _c_) and posterior (_b_) facial
veins near the ventral border of the sternomastoid muscle. It passes
thence obliquely across the sternomastoid to the triangular interval
between it and the clavotrapezius. In the interval it receives a small
branch which accompanies the branch of the transversa scapulæ artery to
the clavobrachialis muscle, receives next the common trunk of the vena
cephalica and transversa scapulæ, and opposite the cranial end of the
manubrium receives the internal jugular vein (Fig. 129, _l_). It then
unites with the subclavian to form the innominate vein. Near the point
where it receives the internal jugular the external jugular vein
receives the =thoracic duct= (Fig. 118, 5).

Branches of the external jugular:

_a._ =V. transversa scapulæ.=--This follows the course of the artery of
the same name. One of its branches receives one of the two terminal
divisions of the vena cephalica (q. v.). In many cases veins which
correspond to branches of the transversa scapulæ artery enter the
external jugular separately (as shown in Fig. 118, _x_ and _y_).

_b._ =V. cervicalis ascendens.=--A small branch which follows the
corresponding branch of the thyrocervical axis.

_c._ =V. jugularis interna= (Fig. 118, 2; Fig. 119, page 284).--The
internal jugular vein varies much in size and in the place where it
joins the external jugular. The point of junction is usually at about
the level of the first rib, but may be much farther craniad. It arises
on the ventral side of the basal portion of the occipital by the
junction of a number of veins which are described below. The internal
jugular passes caudad in the neck region at the side of the trachea, in
company with the common carotid artery and the vagus and sympathetic
nerves. In this region it receives branches which accompany the branches
of the common carotid artery.

The veins which by their union form the internal jugular vein are the
following:

(1) One or two veins from the venous sinuses of the brain, leaving the
cranial cavity by the jugular foramen. These are described in the
account of the veins of the brain.

(2) A large communicating branch from the posterior facial.

(3) The =vena occipitalis=, a large branch coming from the vertebral
column (which it leaves by the atlantal foramen) and from the back of
the head.

_d._ =V. facialis anterior= (Fig. 131, _c_).--The anterior facial vein
collects the blood from the face, the tongue, and adjacent parts; it
joins the =posterior facial= (_b_) caudad of the angle of the jaw to
form the external jugular vein.

The anterior facial begins over the frontal bone caudad of the orbit,
where it is known as the =frontal= vein (_c″_). This runs along the
dorsal border of the orbit, into which it dips. It sends a communicating
branch into the orbit, and receives small veins (=superior palpebral=)
from the upper eyelid. It then turns ventrad, passing along the cranial
angle of the eye between the levator labii superioris proprius (5) and
the orbicularis oculi (8) muscles, being called in this region the
=angular vein= (_c′_). This receives branches (=external nasal veins=,
_k_) from the side of the nose. The vein crosses the malar bone
obliquely (now receiving the name =anterior facial=, _c_) and follows
the cranioventral border of the masseter muscle (9). As it passes the
infraorbital foramen it receives through the foramen a small vein from
within the orbit. It receives also the =inferior palpebral= (_j_) from
the lower eyelid, and the =superior labial= vein (_i_) from the upper
lip. Just caudad of the angle of the mouth it receives from beneath the
cranioventral margin of the masseter the =V. facialis profunda= (_h_)
described below. Still farther caudad it receives the =inferior labial=
vein (_g_) from the lower lip, and a small branch from the masseter
muscle. Caudad of the middle of the cranioventral border of the masseter
it receives from beneath the lymphatic gland of this region the large
=submental= vein (_f_). Next the anterior facial vein receives a large
communicating branch (=V. transversa=, _d_) which passes transversely
across the ventral surface of the throat and connects the two anterior
facial veins of the opposite sides. From the middle of this
communicating branch an unpaired trunk passes caudad in the middle line
and divides into the two =laryngeal= veins, which pass to the larynx; a
small branch is continued from the unpaired trunk craniad into the
tongue. The communicating branch receives also near its junction with
the anterior facial a rather large superficial branch (_e_) which comes
from the sides of the lower jaw and passes across the lymphatic gland
(12) to join the communicating branch.

  [Illustration: FIG. 131.--SUPERFICIAL VEINS AND ARTERIES OF THE FACE.

  _a_, external jugular vein; _b_, posterior facial vein; _c_, anterior
  facial vein (_c′_, angular vein; _c″_, frontal vein); _d_,
  communicating branch with opposite anterior facial; _e_, superficial
  branch from lower jaw; _f_, submental vein; _g_, inferior labial vein;
  _h_, deep facial vein; _i_, superior labial vein; _j_, inferior
  palpebral vein; _k_, external nasal veins; _l_, posterior auricular
  vein; _m_, superficial temporal vein; _n_, anterior auricular vein;
  _o_, external maxillary artery; _p_, inferior labial artery; _q_,
  superior labial artery; _r_, infraorbital arteries; _s_, superficial
  temporal artery; _u_, anterior auricular branch of posterior auricular
  artery. 1, M. adductor auris superior; 2, M. corrugator supercilii
  medialis; 3, M. corrugator supercilii lateralis; 4, M. levator labii
  superioris alæque nasi; 5, M. levator labii superioris proprius; 6, M.
  myrtiformis; 7, M. orbicularis oris; 8, M. orbicularis oculi; 9, M.
  masseter; 10, parotid gland; 11, submaxillary gland; 12, lymphatic
  glands.]

The following larger branches of the anterior facial are not described
above:

=V. facialis profunda= (Fig. 131, _h_).--The deep facial vein enters the
anterior facial from beneath the masseter, just caudad of the angle of
the mouth. It collects branches from the soft and hard palates and the
teeth, these branches passing along with the corresponding arteries for
a distance, then uniting and passing ventrolaterad beneath the zygomatic
arch to join the anterior facial. The deep facial vein also receives
branches which come from the venous plexus that lies in the same region
as the arterial carotid plexus.

=V. submentalis= (Fig. 131, _f_).--This enters the anterior facial vein
at the ventral border of the masseter muscle and near the cranial end of
the two superficial lymph-glands (12) in this region. The submental vein
is formed at the dorsal border of the digastric muscle by two branches
emerging from between the digastric and the mandible. The more cranial
of these, =V. lingualis=, collects branches from the tongue, from its
middle to the tip; it passes through the middle of the lateral border of
the mylohyoid muscle to join the other branch. The second branch emerges
from between the mandible and the pterygoid muscles. It comes from near
the caudal end of the mandible, where it becomes continuous with a
communicating branch from the posterior facial vein, and receives a
branch which comes from the mandibular canal; also small branches from
the adjacent parts.

_e._ =V. facialis posterior= (Fig. 131, _b_).--The posterior facial vein
arises from the region of the internal maxillary artery, its terminal
branches following the branches of the artery. It collects blood from
the pterygoid, masseter (9), and temporal muscles, and forms a plexus
which is interwoven with the carotid (arterial) plexus in the region of
the orbital fissure. It is connected with the submental vein by a
communicating branch. From the posterior facial a branch extends ventrad
close against the outer surface of the tympanic bulla and then turns
caudad, receives a branch from the pharynx, then continues to join the
internal jugular. The posterior facial itself passes laterad along the
caudal border of the masseter (9) and the ventral border of the parotid
gland (10), then becomes superficial and turns ventrad over the outer
surface of the submaxillary gland (11) to join the anterior facial (_c_)
caudad of the angle of the jaw.

As it passes ventrad of the parotid gland (10), just before becoming
superficial, the posterior facial receives the =superficial temporal=
(_m_). This at first follows the superficial temporal artery (_s_), then
enters the substance of the parotid gland, joining the posterior facial
near the ventral border of the latter. The superficial temporal receives
the =anterior auricular= (_n_), a large vein passing along the cranial
border of the auricular opening and arising dorsad of the eye.

The posterior facial receives also, at the point where it passes from
beneath the parotid gland, the =posterior auricular= or =great
auricular= vein (_l_). This collects blood from the back of the head and
the external ear, its branches following those of the artery of the same
name. It passes along the caudal border of the parotid gland to join the
posterior facial.


VEINS OF THE BRAIN AND SPINAL CORD.--The veins of the brain form a large
number of small vessels which pour their blood into larger veins lying
in folds of the dura mater; these are known as the =venous sinuses= of
the dura mater. These sinuses communicate with the venous plexus about
the orbital fissure, coming from the posterior facial vein; with the
internal jugular through the jugular foramen, and with the vertebral
veins, in the vertebral canal. The chief sinuses of the dura mater on
the dorsal side of the brain are as follows:

1. =Sinus sagittalis superior.=--This lies in the dorsal part of the
falx cerebri, between the two hemispheres of the cerebrum. It receives
veins from the dorsal and middle parts of the cerebrum, and passes
caudad to the tentorium. Here it enters the sinus transversus. It
receives the =vena cerebri magna=, a large vein coming from the interior
of the brain and passing directly dorsad at the caudal end of the corpus
callosum to enter the sinus sagittalis.

2. =Sinus transversus.=--This lies in a canal in the dorsal border of
the tentorium. It receives numerous small veins from the cerebellum,
roof of the skull, etc. One or two centimeters on each side of the
middle line the sinus transversus passes out of the canal onto the
caudal surface of the tentorium, thence proceeds caudoventrad obliquely
over the surface of the cerebellum, unites with veins from the ventral
side of the brain, leaves the skull by the jugular foramen, forming thus
the =inferior cerebral= vein, and joins the internal jugular vein.

On the ventral side of the brain are the following sinuses of the dura
mater:

3. =Sinus cavernosus.=--A short broad venous sinus, one on each side of
the hypophysis, on the body of the sphenoid. It receives veins from the
side and ventral surface of the brain. The two sinuses are connected by
communicating branches craniad and caudad of the hypophysis. From them
branches pass out through the orbital fissure to join the plexus formed
by the branches of the posterior facial vein.

4. =Sinus petrosus inferior.=--This arises from the sinus cavernosus and
passes caudolaterad in the groove between the edge of the petrous bone
and the basilar portion of the occipital. Reaching the jugular foramen
it divides; part joins the termination of the sinus transversus to form
the =inferior cerebral vein=, which passes through the jugular foramen
to join the internal jugular vein. The other portion of the sinus
petrosus inferior passes through the condyloid canal of the occipital
bone, communicates by a strong transverse branch across the surface of
the basioccipital with the vein of the opposite side, and enters the
spinal canal through the foramen magnum. Here it joins the sinus of the
vertebral column.

5. =Sinus columnæ vertebralis.=--On the ventral surface of the vertebral
canal, beneath the periosteum, are two wide venous sinuses, one on each
side of the middle line. These sinuses extend the entire length of the
spinal cord. At the atlantal foramen each sends a strong branch to the
internal jugular vein. Farther caudad they send branches to the
vertebral, intercostal, and lumbar veins, and communicate with each
other by numerous transverse branches. They receive many small veins
from the spinal cord.


3. =Vena cava inferior= (Fig. 129, _c_; Fig. 126, _a_).

The inferior vena cava (Fig. 126, _a_) is formed at about the level of
the last lumbar vertebra by the union of the two =common iliac= veins
(Fig. 126, _w_). It passes craniad near the dorsal median line, lying at
first dorsad of the aorta (_b_), then to the right, then ventrad. It
enters the substance of the liver in the dorsal part of the caudate lobe
of the latter, passes through the liver, and then through the diaphragm
near the ventrolateral edge of the central tendon. It passes then
craniad in the thoracic cavity (Fig. 129, _c_) ventrad of the caudal
lobe of the right lung, and enters the right auricle.

It receives the following branches (Fig. 126): =lumbar=, =iliolumbalis=
(_v_), =spermatica interna= (_u_), =renal= (_t_), =adrenolumbalis=
(_s_), =phrenic=, and =hepatic= veins. All but the last two named
accompany the arteries of the same name.

=V. phrenica.=--The phrenic veins gather the blood from the diaphragm
and empty into the vena cava as it penetrates the diaphragm.

=V. hepatica.=--The hepatic veins vary in number. They gather the blood
from the liver (sent in by the portal vein and hepatic arteries) and
enter the vena cava just caudad of the diaphragm.


VENA PORTÆ. THE PORTAL VEIN (Fig. 131).--The =portal= vein is the large
vein carrying the blood from the abdominal viscera to the liver. Within
the liver the portal vein breaks up into capillaries; these collect to
form the =hepatic= veins, which enter the vena cava inferior. The portal
vein (_a_) is formed near the pyloric end of the stomach (1) by the
union of the =superior mesenteric= (_b_) and =gastrosplenic= (_c_) veins
and passes thence along the ventral border of the foramen epiploicum
(foramen of Winslow) to the liver (2), where it divides, going to the
lobes of the liver. On its way to the liver it may receive the
=pancreaticoduodenalis= (_d_), =gastroepiploica= (_e_), and =coronaria
ventriculi= (_f_). These may unite with the portal separately, or any
two or all three may unite to form a single trunk before entering the
portal vein.

1. =V. coronaria ventriculi= (_f_) gathers the blood from the lesser
curvature of the stomach and anastomoses with the gastrosplenic veins.
It usually empties into the portal vein near the pylorus.

2. =V. pancreaticoduodenalis= (_d_) receives the blood from the pancreas
and first part of the duodenum, and empties into the vena portæ near to
or with the preceding.

  [Illustration: FIG. 132.--PORTAL VEIN.

  _a_, portal vein; _b_, superior mesenteric; _c_, gastrosplenic; _d_,
  pancreaticoduodenalis; _e_, gastroepiploica; _f_, coronaria
  ventriculi; _g_, _h_, _i_, branches of gastrosplenic; _j_, inferior
  mesenteric. 1, stomach; 2, liver; 3, duodenum; 4, spleen.]

3. =V. gastroepiploica= (_e_) comes from the greater curvature of the
stomach and ascending limb of the great omentum. It empties into the
vena portæ ventrodextrad of the opening of the coronaria ventriculi, or
sometimes in common with it.

4. =V. gastrolienalis= (_c_).--The gastrosplenic is one of the veins
which unite to make up the portal vein. It is formed by three branches:
one (_g_) from the horizontal or gastric portion of the pancreas, one
(_h_) from the stomach and gastric end of the spleen, the third and
largest (_i_) from the caudal end of the spleen and descending limb of
the great omentum. The three branches unite and the common trunk joins
the superior mesenteric vein (_b_) to form the portal vein as above
described.

5. =V. mesenterica superior= (_b_).--The superior mesenteric vein
receives the blood from the small and large intestines. It is formed by
numerous branches which follow and have the same name as the
corresponding arteries. It receives also the =inferior mesenteric= (_j_)
from the large intestine. The numerous branches unite, and the main
trunk thus formed joins the gastrosplenic (_c_), and the two united
become the portal vein (_a_).

VENA ILIACA COMMUNIS. COMMON ILIAC VEIN (Fig. 126, _w_; Fig. 127, page
310).

The common iliac veins (Fig. 126, _w_) are the two large vessels which
unite in the sacral region to form the inferior vena cava (_a_). Each is
a large vessel, usually four or five centimeters in length, which is
formed by the junction of the large =external iliac= vein with the
smaller =hypogastric= vein (_z_). The left common iliac usually receives
the =V. sacralis media= (_o_); other lateral branches are as a rule not
received by the common iliac veins.

There is much variation as to the formation of the common iliac veins
and their union to form the vena cava. On this subject the paper by
McClure, in the _American Naturalist_, vol. XXXIV. pp. 135-198 (March,
1900), may be consulted with profit. The more typical variations may be
classified as follows: (1) The two common iliac veins may be longer than
usual, so that the vena cava is formed farther craniad than usual. (2)
There may be in the abdominal region two separate veins (=venæ
cardinales=) representing the inferior vena cava, these uniting in the
region of the kidneys. (3) The vena sacralis media may enter into the
left common iliac (the usual condition); or the right common iliac (as
in Fig. 126); or it may fork, one branch passing to the left, the other
to the right common iliac.

Branches of the common iliac veins:

1. =V. sacralis media= (Fig. 126, _o_).--This follows the course of the
corresponding artery and usually enters the left common iliac.

2. =V. hypogastrica= (or =iliaca interna=) (_z_).--The hypogastric or
internal iliac vein joins the medial side of the external iliac to form
the common iliac (_w_). Its branches follow the branches of the
corresponding artery except that the vein from the bladder (umbilical
vein) joins the =V. hemorrhoidalis media=. Also the =vena glutea
inferior= receives a large superficial communicating branch (Fig. 163,
_k_′) from the =vena saphena parva=. This branch leaves the saphena
parva (Fig. 163, _k_) at the popliteal space, and passes over the
lateral surface of the biceps muscle to its proximal end. Here it passes
between the biceps and caudofemoralis to join the vena glutea inferior.

3. =V. iliaca externa= (Fig. 127, page 310).--This vein follows the
corresponding artery, collecting the blood from the posterior extremity.
Its branches are the same and have in general the same distribution as
those of the artery. The vein has, however, certain branches in addition
to those of the artery, resulting in a somewhat different general
arrangement of vessels; it will be necessary therefore to give an
account of the system of veins from the foot and lower leg.

The blood is collected from the foot into two sets of veins which may be
distinguished as the _deep_ and the _superficial_ sets. The veins of the
deep set are those which accompany the branches of the popliteal and
anterior tibial arteries. Those of the superficial set are larger and
carry most of the blood. On the dorsum of the foot blood is collected
from the third, fourth, and fifth digits by two or three superficial
metatarsal veins, which unite opposite the proximal end of the
metatarsus into a single vein. This receives a similar branch coming
from the dorsum of the second digit, and has numerous branches in the
ankle region which form here a network, communicating with the vena
saphena parva (Fig. 163, _k_), and with branches from the plantar side
of the foot. From this network two or three main veins pass proximad on
the medial side of the leg, along with the branches of the arteria
saphena, and unite with a similar vein from the plantar side of the foot
to form the vena =saphena magna= (Fig. 127, _k_, page 310), which
accompanies the arteria saphena to join the femoral vein (_a_).

On the plantar side of the foot small veins pass from the digits to a
superficial =venous plantar arch=, which lies just proximad of the
fibrous pad on the sole of the foot. At its medial side this arch
extends proximad and dorsad to join that branch of the vena saphena
magna which comes from the dorsum of the second digit. On the lateral
side it extends proximad along the lateral margin of the foot, sends a
communicating branch dorsad to the branches of the V. saphena magna, and
continues along the lateral border of the foot to the ankle. It forms
the beginning of the =V. saphena parva= (Fig. 163, _k_, page 401). This
receives branches from the lateral surface of the ankle, which
anastomose with those of the saphena magna. The saphena parva then
passes proximad along the lateral surface of the leg, close to its
ventral border, to the popliteal space. At the distal end of the
popliteal space it divides into two branches. One passes inward through
the fat of the popliteal space, receiving branches from the lymphatic
gland situated here, and joins the popliteal vein. The other (_k_′)
remains superficial and continues proximad over the lateral surface of
the biceps to the proximal end of that muscle. Here it passes between
the biceps and caudofemoralis to join the inferior gluteal vein.


IV. THE LYMPHATIC SYSTEM. SYSTEMA LYMPHATICUM.

The lymphatic system of the cat has not been worked out in detail, so
that only the main features of the system are given in the following
account.

The lymphatic system consists of a number of vessels, the =lymphatics=,
containing a colorless fluid called =lymph=, and of =lymphatic glands=,
connected with the lymphatic vessels. The lymphatic vessels are found
throughout the body as slender tubes, frequently united into networks,
and containing many valves. They take origin from the spaces in the
connective tissue, so that they are at first without definite walls. The
fluid in the connective-tissue spaces gradually flows together into
tubes with definite walls, and these tubes, the lymphatic vessels,
finally join the venous system. In their passage through the lymphatic
glands the vessels break up into fine channels which again unite on
leaving the gland. In the gland lymph-cells are added to the fluid, and
probably other changes are produced.

Most or all of the lymphatic vessels of the body finally unite into two
trunks before entering the veins. The largest trunk is the =thoracic
duct= (Fig. 118, 5, page 282), which collects the lymph from the entire
caudal half of the body, and from the left forelimb and the left side of
the thorax, head, and neck. It passes along the dorsosinistral side of
the thoracic aorta, lying against its surface, and enters the left
external jugular vein at its junction with the subclavian. The second
main trunk is the =right lymphatic duct=; this collects the lymph from
the right side of the thorax, the right forelimb, and the right side of
the neck and head; it enters the right external jugular.


1. =Lymphatics of the Head.=--A number of lymphatic vessels arise on the
sides of the face, especially in the upper and lower lips. They form a
superficial network of vessels, lying over the ventral half of the
masseter muscle and an area ventrad of it. These lymphatic vessels all
enter two large lymphatic glands (Fig. 131, 12, page 322) lying at the
ventrocaudal angle of the masseter muscle, covering the union of the
anterior and posterior facial veins. Into these glands pass also a
number of lymph vessels from the back of the head. From these two
lymphatic glands two or three small lymphatic vessels pass caudad, lying
on the surface of the external jugular vein. Near the point of the
shoulder, some distance craniad of the junction of the external and
internal jugular veins, these vessels enter another small lymphatic
gland lying on the dorsal surface of the external jugular vein. Thence
one or two vessels continue caudad, still on the surface of the external
jugular, and finally unite with the deep lymphatics of the head and neck
and those of the arm to enter the caudal end of the external jugular
vein, usually (on the left side) after junction with the =thoracic
duct=, from the thorax.

The deep lymphatics of the head come from the internal parts of the
head,--tongue, pharynx, etc., and enter a large lymphatic gland situated
close to the caudoventral surface of the tympanic bulla, at the side of
the pharynx. Thence a large lymphatic trunk passes caudad at the side of
the trachea, along with the common carotid artery and internal jugular
vein, unites with the superficial vessels from the head, above
described, joins (on the left side) the thoracic duct, and enters the
external jugular vein.


2. =Lymphatics of the Neck.=--Two or three lymph-glands are found in the
fatty mass in the neck beneath the clavotrapezius and levator scapulæ
ventralis muscles. These receive lymphatics from the neck and side of
the thorax. The vessels which arise from them join those from the head
and arm to enter the external jugular vein.


3. =Lymphatics of the Thoracic Limbs.=--The lymphatics of the forelimbs
begin as a number of vessels on the dorsum and palm of the hand. These
all pass toward the radial side, and at about the base of the first
metacarpal the vessels from both sides of the hand unite to form two or
three main trunks. These pass towards the elbow, accompanying the vena
cephalica (Fig. 130). There are usually two of these main trunks, one
lying on each side of the vena cephalica. They accompany this vein over
the shoulder, following that portion which finally joins the external
jugular. In the hollow of the shoulder they enter the =cervical
lymph-glands=, one or two lymph-glands imbedded in the fat lying beneath
the clavotrapezius and levator scapulæ ventralis in this region. From
the cervical lymph-glands a single trunk passes mediocaudad, unites with
the lymphatics from the head, and usually (on the left side) with the
cranial end of the thoracic duct, and enters the external jugular vein
at its junction with the subclavian. The common trunk from the head and
arm may enter the jugular separately, but close to the termination of
the thoracic duct. On the right side the common trunk is joined by one
or more small vessels coming from the lymphatic glands of the thorax and
forming the right lymphatic duct.

There is said to be also a deep system of lymphatics in the arm, in
addition to the superficial system above described; this is said to
accompany the branches of the brachial vein. If this system is present
in the cat, it is much less easily demonstrated than the superficial
system.


4. =Lymphatics of the Thorax and Abdomen.=--In the thorax are a number
of lymphatic glands which are apparently not constant in number and
position. One is commonly found dorsad of the bifurcation of the
superior vena cava, one ventrad of the mammary vein, several small ones
about the bifurcation of the trachea, one or more in the region of the
aortic arch, and a number of small ones scattered in the mediastinum.
The vessels from these glands finally join either the right lymphatic
duct or the thoracic duct; the details have not been worked out and are
probably variable.

In the abdominal cavity a number of =mesenteric= glands, of considerable
size, are found in the mesentery and in the mesocolon. In the mesocolon
these are usually separate, forming a chain of glands following the
colon about one and a half centimeters from it. In the mesentery the
glands are mostly united into a very large one, formerly known as the
=pancreas aselli=; this is the largest lymph-gland in the body. It is a
curved structure, four or five centimeters in length, lying in the
central region of the mesentery.

Into the mesenteric glands pass lymphatic vessels from the viscera of
the abdomen. From the mesenteric glands one or two large lymphatic
vessels pass craniodorsad, at first with the portal vein, then dorsad of
it. This vessel reaches the dorsal side of the aorta near the cranial
end of the kidney, where it enters a large fusiform vessel, the
=receptaculum chyli=, which stretches from the cranial end of the kidney
craniad between the crura of the diaphragm into the thorax. The
receptaculum receives other lymphatics from the various organs of the
abdominal cavity as well as vessels coming from the pelvic region, and
from the =iliac= glands. These lie beside the iliac artery, receive
lymphatics from the hind limbs, and send lymphatics craniad to the
receptaculum chyli. The latter forms the beginning of the =thoracic
duct=.

The thoracic duct (Fig. 118, 5, page 282) enters the thoracic cavity
between the crura of the diaphragm as a continuation of the receptaculum
chyli. It lies on the dorsal side of the aorta (_a_), somewhat to the
left. It passes along the aorta, gradually coming to lie more on its
left side, and finally leaves that vessel near the aortic arch. The duct
continues thence straight craniad along the left side of the œsophagus
till it reaches the external jugular vein at its junction with the
subclavian. In this region the thoracic duct usually unites with the
lymphatics coming from the head and arm, then enters the external
jugular vein, or the innominate at the point of union of external
jugular and subclavian.

In its passage through the thorax the duct frequently divides into two
or three divisions which pass along parallel to each other for a
distance, then reunite. Such division into two or three parts is
especially frequent just before the union with the jugular vein. The
numerous valves in the thoracic duct give it a beaded appearance.


5. =Lymphatics of the Pelvic Limbs.=--A number of lymphatic vessels are
formed on the dorsum and the sole of the foot. These pass to the lateral
side, forming a network on the lateral and dorsal surface of the
ankle-joint, and finally unite into two main trunks which accompany the
vena saphena parva. In the popliteal space these enter the =popliteal
gland= which lies imbedded in the fat of that region. From the popliteal
gland one or two trunks accompany the superficial division of the vena
saphena parva across the lateral surface of the biceps muscle, and
finally thus reach the pelvic cavity. Here they join the lymphatics of
the pelvic region, which all pour their lymph at last into the thoracic
duct. Inguinal glands are either very small or not present in the cat.

The pelvic limbs have perhaps a deep system of lymphatics, accompanying
the deep veins; if so, they are not easily demonstrable.

  [Illustration: FIG. 133.--CRANIAL PORTION OF THE SPINAL CORD, WITH THE
  CERVICAL ENLARGEMENT. DORSAL VIEW.

  1-8, the eight cervical nerves. _I_-_II_, first two thoracic nerves.
  _a_, dorsal roots (ventral roots not shown); _b_, spinal ganglia; _c_,
  dorsal rami; _d_, ventral rami; _e_, posterior median sulcus; _f_,
  posterior lateral sulcus.]



NERVOUS SYSTEM.


I. THE CENTRAL NERVOUS SYSTEM.


1. =The Spinal Cord. Medulla spinalis= (Figs. 133-136).--The spinal cord
is that portion of the nervous system which occupies the vertebral
canal; it is continuous craniad with the brain. It has the form of a
somewhat flattened cylinder and extends from the foramen magnum into the
caudal region. It diminishes in diameter after entering the sacral
region.

The cord has a cervical and a lumbar enlargement, the former (Fig. 133)
marking the origin of the nerves which pass to the fore limb, and the
latter (Fig. 136) the origin of those which pass to the hind limb.

The =cervical= enlargement (Fig. 133) lies in that part of the vertebral
canal bounded by the fourth to seventh cervical and first thoracic
vertebræ. Caudad of the first thoracic vertebra the cord continues of
nearly uniform diameter to the lumbar enlargement (Fig. 136) which
stretches from the third to the seventh lumbar vertebræ (inclusive).
Caudad of the seventh lumbar vertebra it diminishes uniformly in
diameter and ends in a slender cord, the =filum terminale= (Fig. 136,
_C_), which may be traced into the caudal region.

The surface of the cord is marked by a number of longitudinal grooves or
=sulci=, and =fissures=. The most prominent of these is the =anterior
median fissure= (Fig. 134, _c_), along the ventral median line; into
this the pia mater dips. The =posterior median sulcus= (Fig. 133, _e_;
Fig. 134, _a_) is a shallow furrow along the dorsal median line. The
anterior fissure and the posterior sulcus thus divide the cord into
lateral halves. Each half is subdivided by the =anterior= and =posterior
lateral sulci=.

The =posterior= lateral sulcus (Fig. 133, _f_; Fig. 134, _b_) lies at
the side of the posterior median sulcus. It is broad and shallow and
has the posterior roots of the spinal nerves emerging from its bottom.

The =anterior= lateral sulcus exists only after the forcible pulling out
of the anterior (ventral) roots of the spinal nerves. It then marks the
line along which they originate from the cord.

In cross-section (Fig. 134) the substance of the cord appears to the
naked eye as composed of a darker central “=gray matter=” (_g_) and of
an outer “=white matter=” (_f_). The gray matter has in section the form
of the letter H. The cord is really tubular, having a =central canal=
(_h_) which appears in section in the middle of the cross-bar of the H,
while the two ends of each vertical bar extend toward the anterior and
posterior lateral fissures.

The white matter is divided into funiculi (or columns) by the fissures
and sulci, so that there is in each half of the cord an =anterior=, a
=posterior=, and a =lateral= white funiculus.

In the cervical region (Fig. 134) there appears between the posterior
lateral and posterior median sulci an =intermediate= sulcus which
divides the posterior funiculus in this region into two. The median
slenderer of these is the =fasciculus gracilis= (_d_) or column of Goll.
The lateral and thicker is the =fasciculus cuneatus= (_e_) or column of
Burdach.

_The membranes of the spinal cord_:

The =dura mater= is a tough fibrous membrane directly continuous with
the dura mater of the brain. It differs from the dura mater of the brain
in two particulars:

1. At the foramen magnum it splits into two layers, one of which lines
the bony vertebral canal and forms its periosteum, while the other
covers the cord.

2. It is separated from the cord by a considerable space. The dura mater
is continuous with the fibrous sheaths of the spinal nerves at their
points of exit. Along the sides of the cord it is connected to the pia
mater by a delicate strand of connective tissue probably equivalent to
the “ligamentum denticulatum” of man.

The =arachnoid= is a delicate cellular membrane lying beneath the dura
mater, between it and the pia mater. It forms a continuous investment
for the cord, is not vascular, and is said not to dip into the fissures
of the cord.

  [Illustration: FIG. 134.--CROSS-SECTION OF THE SPINAL CORD IN THE
  CERVICAL REGION.

  _a_, posterior median sulcus; _b_, posterior lateral sulcus; _c_,
  anterior median fissure; _d_, fasciculus gracilis; _e_, fasciculus
  cuneatus; _f_, white matter; _g_, gray matter; _h_, central canal.]

  [Illustration: FIG. 135.--SECTION OF SPINAL CORD, SHOWING THE ORIGIN
  OF A PAIR OF SPINAL NERVES.

  _a_, dorsal root; _b_, spinal ganglion; _c_, dorsal ramus; _d_,
  ventral ramus; _e_, ventral root.]

  [Illustration: FIG. 136.--CAUDAL PORTION OF THE SPINAL CORD.

  _A_, lumbar enlargement; _B_, cauda equina; _C_, filum terminale; 5-7,
  fifth to seventh lumbar nerves. _I_-_III_, the three sacral nerves.
  _a_, dorsal roots; _b_, spinal ganglia; _c_, dorsal rami; _d_, ventral
  rami.]

The =pia mater= invests the cord closely and contains some
blood-vessels. It is a delicate membrane which dips into the fissures
and sulci of the cord and is connected to it by numerous strands of
connective tissue that pass from it into the substance of the cord. The
nerves pierce it.

=Spinal Nerves.=--From the spinal cord arise the spinal nerves. Of these
there are about thirty-eight pairs in the cat. Eight are =cervical=,
thirteen =thoracic=, seven =lumbar=, three =sacral=, and seven or eight
=caudal=. Those leaving the cervical (Fig. 133, 5-8 and _I_) and lumbar
(Fig. 136) enlargements are larger than the others. The =first= cervical
nerve leaves the vertebral canal through the atlantal foramen, the
=second= leaves between the arches of the atlas and axis, while all
the others leave the vertebral canal by way of the intervertebral
foramina. Each nerve arises from the cord by a =dorsal= and a =ventral=
root. The dorsal root is chiefly sensory, the ventral motor in
character. The =dorsal= root (radix posterior) (Figs. 133, 135, and 136,
_a_) begins as a number (twelve or more) of separate nerve-bundles which
emerge from the posterior lateral groove. These roots lie nearly in a
single plane and pass laterad, converging to penetrate a ganglion, the
=spinal ganglion= (_b_) (or ganglion of the posterior root). All the
spinal ganglia except the first and second are situated in the
intervertebral foramina or within the vertebral canal. The first and
second are situated among the muscles surrounding the place of exit of
the nerves.

The =ventral root= (radix anterior) (Fig. 135, _e_) arises as a larger
number of small fibre-bundles which do not lie in a single plane, so
that in a transverse section several rootlets may appear in a single
section. The rootlets converge to form a single mass which joins the
dorsal root just as it emerges from the spinal ganglion. The nerve
formed by the junction of the ventral and dorsal roots is one of the
=spinal nerves=.

The direction in which the nerves leave the cord varies. In the cervical
region (Fig. 133) and cranial part of the lumbar region it is nearly
laterad; at the cervical and lumbar enlargements it is laterocaudad. The
nerves in the sacral and caudal regions pass almost directly caudad to
reach the intervertebral foramina and form thus a brush which surrounds
the filum terminale (Fig. 136, _C_) and is called the =cauda equina=
(Fig. 136, _B_).

Each spinal nerve immediately after leaving the intervertebral foramen
divides into two branches, a =dorsal= or =posterior= branch or =ramus=
(_c_), and a =ventral= or =anterior ramus= (_d_). The dorsal ramus is in
each case small (except in the first and second cervical nerves), and is
distributed to the longitudinal muscles and integument of the back.

The ventral rami are larger and each is connected a short distance
beyond its origin with the sympathetic system by a short =ramus
communicans= or communicating branch. Each is then distributed to the
integument and muscles of the ventral part of the body, including the
limbs.

The ventral rami which pass to the limbs are much larger than the
others. The ventral rami are further distinguished from the dorsal by
the fact that they frequently unite with one another to form plexuses.

The peripheral distribution of the spinal nerves is described later.


2. =The Brain. Encephalon.=--The brain is that portion of the central
nervous system that is included within the cranial cavity. It is a
direct continuation of the spinal cord, and presents many of the same
essential characters as the latter, with great modifications in details.

The structure of the brain can best be understood if it be considered as
a modified continuation of the spinal cord, and the relation of the
parts to the essential parts of the cord noted. The spinal cord is a
nearly straight tube, with a central cavity and thick walls. The brain
is likewise tubular, with the cavities enlarged or subdivided in places,
with the walls greatly thickened, and with a number of bends and
constrictions in the tube. The relation of the structure of the brain to
that of the spinal cord is most easily perceived by an examination of
the brain of some lower vertebrate, as the frog or shark, and such an
examination should be made before proceeding to the study of the more
complicated brain of the cat.

In the following account of the brain of the cat all parts will be
described as far as possible in relation with the tubular structure of
the brain. The brain will be considered as a hollow structure, having
central cavities, and the solid portions will be brought into relation
as parts of the roof, sides, or floor of the cavities. The cavities of
the brain, forming a direct continuation of the central canal of the
spinal cord, are known as =ventricles= (=ventriculi=).

  [Illustration: FIG. 137.--DORSAL SURFACE OF THE BRAIN.

  _I_, olfactory bulbs; _II_, cerebral hemispheres; _III_, cerebellum;
  _IV_, medulla. _a_, præsylvian sulcus; _b_, cruciate sulcus; _c_,
  sulcus ansatus; _d_, coronal sulcus; _e_, anterior sulcus; _f_,
  posterior sulcus; _g_, suprasylvian sulcus; _h_, separate parts of the
  lateral sulcus; _i_, end of splenial sulcus; _j_, vermis of
  cerebellum; _k_, hemispheres of cerebellum; _l_, roof of fourth
  ventricle; _m_, first cervical nerve. 1, orbital lobe (or gyrus); 2,
  sigmoid gyrus; 3, anterior sylvian gyrus; 4, ectosylvian gyrus; 5,
  suprasylvian gyrus; 6, posterior sylvian gyrus; 7, parts of marginal
  gyrus; 8, gyrus compositus posterior.]

In a general view of the cat’s brain from the dorsal side (Fig. 137)
four subdivisions are discernible. At the caudal end is a small
stalk-like portion (_IV_) which is clearly a slightly modified
continuation of the spinal cord; this is the =myelencephalon= or
=medulla oblongata=. Just craniad of this, rising high above it, is an
irregularly lobulated rounded portion, the =cerebellum= (_III_). This is
produced as a thickening of the wall of the original tube; it forms the
dorsal part of the =metencephalon=. These two portions of the brain have
a common cavity, lying within the medulla oblongata and ventrad of the
cerebellum, and formed by a widening of the cavity of the spinal cord;
it is known as the =fourth= ventricle. Craniad of the cerebellum,
separated from it by a deep transverse fissure, are two very large
portions, the =hemispheres= of the =cerebrum= (_II_), separated from
each other by a deep longitudinal fissure; they constitute together the
=telencephalon=. The hemispheres are produced by a sort of forking of
the original central tube;--by outgrowths on the sides of the tube, the
central cavity extending into the outgrowths. The two outgrowths extend
dorsad, as well as craniad and caudad from the original place of origin,
forming the larger part of the brain; the extensions of the central
cavity which they contain are known as the =lateral ventricles=.
Finally, in front of the two hemispheres are seen the two small
=olfactory bulbs= (_I_) which are mere extensions of the two hemispheres
and contains cavities which are extensions of the lateral ventricles.

In a ventral view of the entire brain (Fig. 138) certain parts are
visible which in the dorsal view are hidden by the large cerebral
hemispheres. At the caudal end is seen, as before, the medulla
oblongata, or myelencephalon, and craniad of this, on the ventral side
of the cerebellum, a broad transverse tract, the =pons= (_i_); this,
like the cerebellum, forms part of the metencephalon. All this part of
the brain formed by the myelencephalon and metencephalon lies caudad of
(behind) the rest of the brain and is marked off from it by a great
fissure; it therefore receives as a whole the name hindbrain or
=rhombencephalon=.

Just craniad of the pons are seen two short diverging arm-like bands of
fibres (_g_), enclosing a small triangular space between them. These two
arms with the space between them are all that is visible of a division
of the brain which in dorsal view is completely covered by the backward
projection of the cerebral hemispheres. This is the midbrain or
=mesencephalon=. In this portion of the brain the continuation of the
central cavity is a narrow canal which receives the name =cerebral
aqueduct= (=aqueductus cerebri=) or aqueduct of Sylvius.

  [Illustration: FIG. 138.--VENTRAL SURFACE OF THE BRAIN.

  _I_-_XII_, the twelve cranial nerves in order; _I_, olfactory bulb;
  _II_, N. opticus; _III_, N. oculomotorius; _IV_, N. trochlearis; _V_,
  N. trigeminus (1, mandibular nerve; 2, maxillary nerve; 3, ophthalmic
  nerve; 4, sensory root); _VI_, N. abducens; _VII_, N. facialis;
  _VIII_, N. acusticus; _IX_, N. glossopharyngeus; _X_, N. vagus; _XI_,
  N. accessorius; _XII_, N. hypoglossus. _a_, tractus olfactorius; _b_,
  substantia perforata anterior; _c_, optic chiasma; _d_, infundibulum;
  _e_, hypophysis; _f_, lobus pyriformis, or tractus postrhinalis; _g_,
  pedunculi cerebri; _h_, substantia perforata posterior; _i_, pons;
  _j_, sulcus basilaris of pons; _k_, semilunar (or Gasserian) ganglion;
  _l_, trapezium; _m_, area ovalis; _n_, area elliptica; _o_, pyramidal
  tracts; _p_, anterior or ventral fissure; _q_, foramen cæcum; _r_,
  anterior lateral sulcus; _s_, first cervical nerve.]

Just craniad of the midbrain is a small rather irregular area, bounded
craniad by the band-like =optic chiasma= (_c_), from which arise the
optic nerves (_II_), and showing caudad of this band a rounded irregular
projection (_e_). This is a fourth division of the brain which is
likewise covered dorsad by the hemispheres; it is the ’tween-brain or
=diencephalon=. Its cavity is known as the third ventricle. Just craniad
of the ’tween-brain, in the median line, is a deep fissure, showing that
here in reality is the termination of the original tube, the further
extension craniad being due to the pushing forward of the lateral
outgrowths, or cerebral hemispheres, which extend in ventral view a
considerable distance further craniad. The hemispheres lie also caudad,
laterad, and dorsad of the midbrain and ’tween-brain, so that these
parts are almost enveloped by the hemispheres. The hemispheres and
’tween-brain are sometimes taken together as forming a single portion,
the forebrain or =prosencephalon=.

  [Illustration: FIG. 139.--DIAGRAM OF BRAIN FROM ABOVE.

  FIG. 140.--DIAGRAM OF BRAIN FROM THE SIDE.

  1, myelencephalon; 2, metencephalon; 3, mesencephalon; 4,
  diencephalon; 5, telencephalon. _a_, canal of the spinal cord; _b_,
  fourth ventricle; _c_, cerebral aqueduct (aqueduct of Sylvius); _d_,
  third ventricle; _e_, lateral ventricle; _f_, interventricular foramen
  (or foramen of Monroe); _g_, lamina terminalis; _h_, olfactory bulb.]

There are thus altogether five principal subdivisions of the brain, each
enclosing a portion of the central cavity. These are the
=myelencephalon=, the =metencephalon= (these two enclosing the =fourth=
ventricle), the =mesencephalon= (enclosing the =cerebral aqueduct=), the
=diencephalon= (enclosing the =third= ventricle), and the two cerebral
hemispheres, constituting together the =telencephalon=, and enclosing
the two =lateral ventricles=. A plan of the brain, considered as a tube
enclosing cavities, is given in Figs. 139 and 140. Fig. 139 shows the
plan considered as viewed from the dorsal side, Fig. 140 in a lateral
view. These figures are of course pure diagrams, showing only what may
be called the _plan_ of structure, and omitting all details. In the
actual conditions many important modifications even of the main
features of the plan are met with.

In the following description the parts of the brain will be taken up in
this order:

  A. RHOMBENCEPHALON (primitive hindbrain).
    1. _Myelencephalon._
    2. _Metencephalon._

  B. MESENCEPHALON (primitive midbrain).
    3. _Mesencephalon._

  C. PROSENCEPHALON (primitive forebrain).
    4. _Diencephalon._
    5. _Telencephalon._

A. RHOMBENCEPHALON.


1. _Myelencephalon._--The myelencephalon or medulla oblongata is
transitional between the spinal cord and the brain. It has in general
the structural peculiarities of the cord, but these undergo in it a
gradual transformation into the arrangements characteristic of the
brain.

It has the form of a flattened and truncated cone, which widens craniad
and is limited at the cranial end by the pons (Fig. 138, _i_) ventrally
and laterally; by the cerebellum (Fig. 137, _III_) dorsally. The cranial
portion of its dorsal surface is overhung by the cerebellum. The points
of origin of the roots of the first pair of cervical nerves (Fig. 138,
_s_) may be taken as indicating the boundary between the spinal cord and
the medulla oblongata; there is no other external marking to show the
limits of the two.

The central canal of that part of the medulla which is overhung by the
cerebellum is greatly widened (Fig. 141, _h_). The cavity thus formed is
flattened and triangular, with the apex of the triangle caudad, and is
the caudal part of the =fourth ventricle= (Fig. 141, _h_). The roof is
very thin (Fig. 143, _n_) and is intimately connected with the pia
mater, so that in removing the latter the thin roof of the fourth
ventricle is removed with it and the cavity of the fourth ventricle is
left exposed. The thin roof of the fourth ventricle is known as the
=velum medullare posterius= (Fig. 143, _n_).

The ventral (anterior) fissure (Fig. 138, _p_) of the cord passes onto
the medulla oblongata and ends at the pons (_i_), its end being slightly
deeper and forming what is known as the =foramen cæcum= (_q_). The
dorsal (posterior) sulcus (Fig. 141, _a_) is well marked; it ends at the
caudal boundary of the fourth ventricle (_h_).

The anterior lateral sulcus (Fig. 138, _r_) may be traced craniad from
the origin of the ventral roots of the first cervical nerves (_s_),
along the lateral border of the area elliptica (_n_), then curving
mediad to the lateral border of the pyramis (_o_), and finally reaching
the pons (_i_). Its position is marked by the origin of the roots of the
hypoglossal nerve (_XII_).

The posterior lateral sulcus (Fig. 141, _b_), marked on the spinal cord
by the origin of the dorsal nerve-roots, curves laterad at the sides of
the fourth ventricle (_h_) owing to the increasing width of the latter,
and ends at an elevated area of oblique fibres, the =area ovalis= (_f_).


The columns or funiculi bounded by the longitudinal fissures present the
following peculiarities:

The anterior white funiculus of the cord is replaced in the medulla by
the =pyramidal tracts= (=pyramides=) (Fig. 138, _o_). The pyramidal
tracts are formed by fibres which emerge from beneath the pons and pass
caudad to disappear just craniad of the level of the first cervical
nerve (_s_). The pyramidal tracts are bounded medially by the anterior
median fissure (_p_), but laterally each is separated from the anterior
lateral sulcus (_r_) over its caudal part by an elongated =area
elliptica= (_n_), the human homologue of which is uncertain. It perhaps
represents the =oliva=.

Laterad of the cranial portion of the pyramids is an irregular area
known as the =trapezium= (_l_) which abuts caudad on the area elliptica
(_n_) and the area ovalis (_m_). The =area ovalis= (Fig. 138, _m_; Fig.
141, _f_) (or zonula Arnoldi) is abroad band of oblique fibres which
passes from the lateral side of the area elliptica craniodorsad to
disappear under the cerebellum.

The posterior white funiculus was divided in the cervical region into
two, the =fasciculus gracilis= (column of Goll) and the =fasciculus
cuneatus= (column of Burdach). The fasciculus gracilis (Fig. 141, _c_)
extends to the caudal end of the fourth ventricle (_h_) and ends there
in an expansion, the =clava= (_d_), which forms the posterior boundary
of the fourth ventricle. The fasciculus cuneatus (_e_) passes laterad on
account of the width of the fourth ventricle and appears to end at the
area ovalis (_f_), but it may be seen passing beneath the area ovalis,
emerging at its cranial border and turning dorsad to enter the
cerebellum. It forms the side walls of a part of the shallow fourth
ventricle.

The lateral funiculi are divided by longitudinal furrows into three
divisions. The dorsal one of these is the =fasciculus cuneatus
lateralis= or column of Rolando (Fig. 141, _g_). It accompanies the
fasciculus cuneatus into the cerebellum.

The entire mass formed by the fasciculus gracilis, the fasciculus
cuneatus medialis, and fasciculus cuneatus lateralis is known as the
=corpus restiforme=, and since its fibres pass into the cerebellum it is
sometimes known as the =pedunculus cerebelli= (or crus cerebelli ad
medullam).

The following cranial nerves arise from the medulla oblongata (Fig.
138).

The twelfth nerve (_XII_) (=N. hypoglossus=) arises by ten or fifteen
rootlets from the ventral surface of the medulla oblongata in the
anterior lateral fissure (_r_) opposite the caudal portion of the area
elliptica (_n_).

The eleventh cranial nerve (_XI_) (=N. accessorius=) arises by numerous
rootlets from the lateral surface of the medulla oblongata and of the
spinal cord as far caudad as the sixth or seventh cervical nerve. These
rootlets join to form a nerve which enters the cranium through the
foramen magnum and is closely associated at its point of exit with the
glossopharyngeal (_IX_) and vagus (_X_) nerves. The line of origin on
the medulla passes between the dorsal and ventral roots of the cervical
nerves and is along the middle of the lateral white funiculi.

The tenth cranial nerve (_X_) (=N. vagus=) arises by about eighteen very
delicate rootlets from the surface of the area ovalis. The rootlets are
divided into a dorsal and a ventral series. The dorsal series (about
twelve) arise in the groove which separates the fasciculus cuneatus
medialis from the fasciculus cuneatus lateralis. The ventral series
arise somewhat ventrad of this groove. These rootlets are to be
distinguished from those of the ninth nerve by their smaller size.

The ninth cranial nerve (_IX_) (=N. glossopharyngeus=) arises from the
area ovalis from a line craniad of the dorsal line of origin of the
vagus roots (_X_) and between these and those of the auditory (_VIII_).
It arises by a number of rootlets which are larger than those of the
vagus (_X_), with which this nerve is closely associated.

The eighth cranial nerve (_VIII_) (=N. acusticus=) appears at the
lateral end of the trapezium (_l_). It arises from an elevation (Fig.
141, _i_) which is continued dorsomediad along the cranial border of the
area ovalis.

The seventh cranial nerve (_VII_) (=N. facialis=) leaves the lateral
border of the trapezium (_l_) near its cranial edge, between the fifth
and eighth nerves. It is much smaller than the eighth nerve.

The sixth cranial nerve (_VI_) (=N. abducens=) arises by about six
bundles from the groove between the pyramids and the trapezii and passes
craniad.


2. _Metencephalon._--The metencephalon includes the =pons= and the
=cerebellum=.

The =pons= (Fig. 138, _i_) is a mass of transverse fibres which forms
the ventral and cranial part of the primitive hindbrain. It is a
modification of the latter brought about by the development of the
cerebellum, and the degree of its development is in direct ratio to that
of the cerebellar and cerebral hemispheres. The pons forms a projecting
mass of fibres which is marked by a median longitudinal groove, the
=sulcus basilaris= (_j_), which indicates the course of the basilar
artery (Fig. 121, _c_). Laterad the fibres of the pons converge somewhat
and turning dorsad disappear in the cerebellum, forming the =brachia
pontis= (Fig. 141, _l_).

The fifth cranial nerve (Fig. 138, _V_) (=N. trigeminus=) arises by two
roots from the caudal border of the pons, near the lateral end. The
ventral root (4) is small; the dorsal one is much larger and soon forms
the large semilunar ganglion (_k_) from which three branches (1, 2, and
3) diverge. The ventral root (4) joins one of these branches (1).

The =cerebellum= (Fig. 137, _III_) is formed by an increase in size of
the cranial portion of the primitive hindbrain. This increase has
affected principally the surface of the roof, so that as the cerebellum
has grown it has been thrown into many folds, the exact form of which
varies in different specimens. The cerebellum has at the same time
increased in size and has thus extended laterad as well as caudad and
craniad. It thus touches the cerebrum in front (separated from it by the
tentorium) and aids it in concealing the midbrain and ’tween-brain in
dorsal view, while caudad in the same view it conceals the greater part
of the medulla. The connections of the cerebellum with adjacent parts of
the brain are also overhung and concealed.

The whole surface of the cerebellum is thrown up into numerous folds or
=gyri=, separated from one another by deep fissures or =sulci=, which
appear at first to render the surface wholly irregular. The entire mass
is, however, divisible into a central portion, which from its
resemblance to a segmented worm is called the =vermis= (_j_) (its
cranial part is the =superior vermis=, and its caudal part the =inferior
vermis=), and into lateral portions, the =hemispheres= (_k_). The
vermis (_j_) occupies a median longitudinal position, and its gyri and
sulci are in the main transverse. It is not directly connected with
adjacent parts, and its ventral surface extends farther caudad and
craniad than that of the hemispheres. The ventral part of the superior
vermis is fitted against the posterior corpora quadrigemina.

The =hemispheres= (_k_) may again be subdivided into groups of gyri
which have received special names. One of these, the so-called
appendicular lobe, fits into the appendicular fossa of the petrous bone.

The cerebellum is connected to the adjacent parts by three tracts of
fibres, sometimes known as crura cerebelli. The tract connecting it with
the medulla oblongata is the =corpus restiforme=; that connecting it
with the pons is the =brachium pontis= (Fig. 141, _l_); these have been
described. A third tract passes craniad to the corpora quadrigemina
(Fig. 141, _p_ and _q_); this is the =brachium conjunctivum= (Fig. 141,
_k_).

The cerebellum is composed of white and gray matter, the latter on the
surface (Fig. 143, _III_). The folds of its surface present thus a
contrivance for increasing the amount of gray matter. The white matter
forms a central mass from which tracts extend into the folds. The whole
mass of white matter has thus in section (more particularly in a
longitudinal section of the vermis) the appearance of a tree, whence the
name =arbor vitæ= (Fig. 143).

The =fourth ventricle= (Fig. 141, _h_; Fig. 143, _m_) is the cavity of
the original hindbrain. It begins caudad at the clava (Fig. 141, _d_) as
a widening and continuation of the central canal of the spinal cord and
extends craniad, becoming wider and passing ventrad of the cerebellum.
It becomes narrower craniad and ends at the posterior corpora
quadrigemina (_p_), where it becomes continuous with the aqueductus
cerebri (Fig. 141, _o_; Fig. 143, _j_). The cavity is shallow and is
encroached upon dorsally by the vermis of the cerebellum (Fig. 143).

The floor of the cavity is known as the =fossa rhomboidea= (Fig. 141,
_h_). It is formed by the continuation of the gray matter which
surrounds the central canal of the cord. It is marked by a median
longitudinal groove. At its widest part are seen two considerable tracts
of white fibres (=striæ medullares=) which pass from near the median
line laterad and extend into the auditory (eighth) nerves. The floor
caudad and craniad of these striæ is marked by a number of elevations
and depressions. Similarly situated elevations in the human brain differ
from one another slightly in color, are made up of gray matter, and are
the centres of origin of most of the cranial nerves. Their homologues in
the cat appear not to have been determined.

The side walls of the fourth ventricle (Fig. 141) are formed by the
following in order, beginning caudad: the =clava= (_d_), the =corpus
restiforme=, =brachium pontis= (_l_), =brachium conjunctivum= (_k_), and
=caudal corpora quadrigemina= (_p_) (=colliculi inferiores=).

The roof (Fig. 143) is formed caudad by a thin layer of non-nervous
matter which is closely associated with the pia mater. This thin layer
is known as the =velum medullare posterius= (_n_). It connects the
dorsal surface of the medulla with the caudal border of the cerebellum.
The pia mater covering this portion of the roof is vascular and is
folded in toward the floor of the ventricle, forming the =choroid
plexus= of the fourth ventricle. In the middle the roof of the fourth
ventricle is the cerebellum, while craniad the roof is the =velum
medullare anterius= (Fig. 143, _l_). This is a thin layer just craniad
of the cerebellum, connecting it with the corpora quadrigemina, and
attached laterally to the brachia conjunctiva. Here the fourth ventricle
narrows craniad and becomes continuous with the slender =aqueductus
cerebri= (Fig. 143, _j_) (aqueduct of Sylvius). The narrowed portion of
the brain is frequently known as the =isthmus rhombencephali=.

  [Illustration: FIG. 141.--DORSAL SURFACE OF MYELENCEPHALON,
  MESENCEPHALON, AND DIENCEPHALON.

  The cerebellum and the greater part of the cerebral hemispheres have
  been removed. _a_, posterior sulcus of cord; _b_, posterior lateral
  sulcus; _c_, fasciculus gracilis; _d_, clava; _e_, fasciculus
  cuneatus; _f_, area ovalis; _g_, fasciculus cuneatus lateralis; _h_,
  fossa rhomboidea or floor of fourth ventricle; _i_, projection formed
  by origin of auditory nerve; _j_, facial nerve; _k_, cut end of
  brachium conjunctivum; _l_, cut end of brachium pontis (_l′_, brachium
  pontis); _m_, velum medullare anterius; _n_, fourth nerve; _o_,
  depression marking caudal end of aqueductus cerebri (aqueduct of
  Sylvius); _p_, caudal corpora quadrigemina (colliculi posteriores);
  _q_, cranial corpora quadrigemina (colliculi anteriores); _r_,
  brachium quadrigeminum inferius; _s_, corpus geniculatum mediale; _t_,
  thalamus; _u_, striæ medullares; _v_, third ventricle; _w_, pulvinar;
  _x_, corpus geniculatum laterale; _y_, corpus striatum; _z_, outlines
  of olfactory bulbs. 1, boundary between hemispheres and ’tween-brain;
  2, pineal body.]

The fourth cranial nerve (Fig. 141, _n_; Fig. 138, _IV_) (=N.
trochlearis=) arises from the brain at the craniolateral angle of the
velum medullare anterius.

B. MESENCEPHALON.


3. _Mesencephalon._--The mesencephalon or midbrain includes the =corpora
quadrigemina= (Fig. 141) and the =pedunculi cerebri= (Fig. 142). In the
primary midbrain there is a pronounced thickening of the walls
accompanied by a reduction of the central canal. The midbrain does not
thus become very large and is concealed in the dorsal view by the
cerebellum and cerebrum, though its floor appears in the ventral view
just craniad of the pons (Fig. 138, _g_). Its narrow canal is the
=aqueductus cerebri= (=aqueduct of Sylvius=) (Fig. 143, _j_). Its roof
forms the =corpora quadrigemina=, and its floor the =pedunculi cerebri=.

In a dorsal view (Fig. 141) the roof is seen to be marked by two pairs
of elevations, the =corpora quadrigemina= (_p_ and _q_). The cranial
pair (_q_) (known as the colliculi superiores) are circular in outline,
surrounded on all sides except the cranial one by a deep groove. From
the cranial side a tract of fibres (=brachium quadrigeminum superius=,
or arm of the cranial corpus) extends craniad and disappears beneath the
thalamus (_t_). Between the anterior or cranial corpora quadrigemina
lies the =pineal body= or epiphysis (corpus pineale) (Fig. 143, _y_;
Fig. 141, 2), a portion of the roof of the ’tween-brain. The caudal
corpora (Fig. 141, _p_) are larger than the cranial ones, and ovoid in
shape with the long axis vertical. They are united in the median line,
and the velum medullare anterius (_m_) stretches between their caudal
borders. The brachium of the caudal corpus quadrigeminum (brachium
quadrigeminum inferius) (_r_) extends craniad and disappears beneath a
considerable elevation, the =corpus geniculatum mediale= (_s_).

Crossing this brachium is seen a small tract of fibres which extends
ventrad, crosses the pedunculus cerebri, and reaches the medial border
of the latter. It is the =tractus transversus peduncularis= (Fig. 142,
_b_). Ventrad of the caudal corpus quadrigeminum is seen a triangular
area of oblique fibres which corresponds in position to the human
lemniscus.

The =pedunculi cerebri= (peduncles of the cerebrum) form the ventral
part of the midbrain. They appear in a ventral view of the entire brain
(Fig. 138) as two broad tracts of fibres (_g_) emerging from beneath the
pons and diverging from one another as they pass craniad, finally
disappearing beneath the cerebral hemispheres. Each is made up of many
fibre-bundles, which are apparent in surface view (Fig. 142). The
peduncles are separated by a small triangular space, which is marked by
a median longitudinal sulcus. In this space, just caudad of the
mammillary bodies, is a small area through which a number of
blood-vessels pass into the brain. This is known as the =posterior
perforated area= (or substance) (Fig. 142, _j_). The cerebral
peduncles (_a_) are crossed by the tractus transversus peduncularis
(_b_) (see above).

The third cranial nerve (Fig. 138, _III_) (=N. oculomotorius=) leaves
the brain at the medial border of the cerebral peduncle (_g_), just
caudad of the tractus transversus peduncularis.

The =aqueductus cerebri= (Fig. 143, _j_; Fig. 153, _d_) (or aqueduct of
Sylvius) is the continuation craniad of the fourth ventricle. It is a
narrow passage, one or two millimeters in diameter, lying dorsad of the
pedunculi cerebri and ventrad of the corpora quadrigemina.

  [Illustration: FIG. 142.--VENTRAL SURFACE OF THE MIDBRAIN AND
  ’TWEEN-BRAIN, WITH THE PONS.

  _a_, pedunculi cerebri; _b_, tractus transversus peduncularis; _c_,
  corpus geniculatum mediale; _d_, optic tract; _e_, optic chiasma; _f_,
  optic nerve; _g_, mammillary bodies; _h_, tuber cinereum; _i_, opening
  for infundibulum (which has been removed); _j_, posterior perforated
  area; _k_, pons. _III_, _V_, _VII_, _VIII_, third, fifth, seventh, and
  eighth cranial nerves.]

C. PROSENCEPHALON.--The prosencephalon or primitive forebrain includes
the =diencephalon= or ’tween-brain and the =telencephalon= or cerebral
hemispheres.


4. _Diencephalon._--The diencephalon or ’tween-brain includes the
=thalami= and the other parts bounding the third ventricle. The
diencephalon is seen in entire brains only in ventral view (Fig. 138,
_c_, _d_, _e_, etc.)

The diencephalon may be considered as forming almost or quite the most
cranial portion of the median nervous tube,--the cranial wall of the
third ventricle (the =lamina terminalis=) (Fig. 143, _d_), ending in the
median line in the deep fissure between the hemispheres of the cerebrum.
Parts of the brain which extend farther craniad than this are lateral
portions, due to the forward growth of the lateral hemispheres. The two
hemispheres of the cerebrum may be considered as lateral outgrowths of
the central ’tween-brain; these outgrowths have extended dorsad,
laterad, craniad, and caudad, so as to cover almost completely the
’tween-brain.

In early stages the cerebral hemispheres are projections from the
_cranial end_ of the ’tween-brain, so that the plane of junction was
nearly transverse, the cranial end of the ’tween-brain joining the
caudal end of the hemispheres. With the increasing size and backward
growth of the latter, the attachment to the ’tween-brain has been
shifted from a cranial to nearly a lateral position, and at the same
time the originally lateral surface of the ’tween-brain has become
nearly caudal. This is shown in Fig. 141, the deep fissure at 1 marking
the line of attachment between the ’tween-brain and the hemispheres. The
dorsoventral plane of junction of ’tween-brain and hemispheres is (as
Fig. 141 shows) not wholly lateral, but oblique, passing from its
cranial end near the middle line caudolaterad.

A second peculiarity of the ’tween-brain lies in the thinness of its
roof. The roof is exceedingly thin and is so intimately connected with
the pia mater that they cannot be removed separately. The ventral thick
floor of the ’tween-brain is directly continuous with the similar floor
of the cerebrum; but where the roof of the ’tween-brain joins the roof
of the cerebrum along the oblique plane already indicated, the roof is
very thin and is intimately connected to the pia mater, and is at the
same time folded into the lateral ventricles to form, together with the
pia mater, the =choroid plexuses= of the lateral ventricles (Fig. 148,
_e_). When the pia mater is removed the thin roof of the brain along the
line of junction of the ’tween-brain and the cerebrum is brought away
and there _appears_ to be a direct communication between lateral
ventricles and the exterior.

We may now take up the parts of the diencephalon in detail.

a. =Thalamus= (Fig. 141, _t_).--The two thalami are large oblique
rounded ridges, forming the sides of the ’tween-brain. They lie just
craniad of the cranial corpora quadrigemina (_q_), but separated from
them by a broad groove, and are completely covered by the caudally
projecting part of the cerebral hemispheres. The medial larger end of
each thalamus is near the middle line; thence the thalamus extends
caudolaterad, and rises at its lateral extremity into a sharply rounded
projection, the =corpus geniculatum laterale= (_x_). From this
projection the thalamus is continued ventrad and then craniomediad as a
large band of fibres, the =optic tract= (=tractus opticus=) (Fig. 142,
_d_), which extends to the optic chiasma (_e_), where it passes into the
optic nerves (_f_). On the caudal border of the thalamus, near the
median line, is a very faint projection, the =pulvinar= (Fig. 141, _w_);
this lies just craniad of the lateral border of the cranial corpus
quadrigeminum (_q_). Just ventrad of the corpus geniculatum laterale
(_x_) is the prominent rounded =corpus geniculatum mediale= (_s_); this
is connected by a prominent ridge, the =brachium quadrigeminum inferius=
(_r_), with the caudal corpus quadrigeminum (_p_). In a similar manner
the =brachium quadrigeminum superius= passes from the cranial corpus
quadrigeminum (_q_) into the thalamus itself.

Between the two thalami there exists a groove, the =sulcus
hypothalamicus=. Over this groove lies the roof of the third ventricle,
forming the =choroid plexus= of the third ventricle (Fig. 143, _w_). The
medial surface of the two thalami are flat and extend directly ventrad,
forming part of the lateral boundary of the third ventricle (Fig. 143,
_h_). The two medial surfaces meet over a considerable area across the
narrow cavity of the third ventricle, and unite, forming the =massa
intermedia= (Fig. 143, _f_) or intermediate mass of the thalamus
(“middle commissure”). This connection of the thalami of the two sides
is thus not a primitive one, forming no part of the roof or floor of the
central cavity, but is a secondary connection due to a growing together
of a part of the two sides of the ventricle across its cavity. Along
the dorsal edge of the medial border of each thalamus passes a distinct
white strand, the =stria medullaris= (Fig. 141, _u_); the two striæ meet
in an arch caudad, lying beneath the pineal body (2).

The thalamus is separated craniolaterad by a groove (1) from the corpus
striatum (_y_), on the floor of the cerebral hemisphere.

_b._ The =roof= of the third ventricle is thin and united with the pia
mater, as already stated. The pia mater bears many blood-vessels, and
the two are folded into the groove between the optic thalami, forming
the =lamina chorioidea epithelialis=, or choroid plexus of the third
ventricle (Fig. 143, _w_). The roof is attached to the dorsomedial
borders of the thalami and becomes continuous with the choroid plexus of
the lateral ventricles (Fig. 148, _e_) at the craniolateral borders of
the thalami.

The =pineal body= (=corpus pineale=) or epiphysis (Fig. 141, 2; Fig.
143, _y_) is a small conical body which is formed as an outgrowth of the
caudal part of the roof of the third ventricle. It lies on the roof of
the brain between the two cranial corpora quadrigemina (Fig. 141, _q_).
It is hollow, containing an extension of the third ventricle. From its
craniolateral angles two white strands, the =habenulæ=, extend into the
striæ medullares (Fig. 141, _u_) of the thalami.

Just ventrad of the pineal body is a transverse band of white fibres,
lying in the caudal part of the roof of the third ventricle. This
interconnects the two thalami, and forms the =posterior commissure=
(Fig. 143, _z′_) (commissura posterior). From this commissure a thin
sheet of tissue extends to the pineal body.

_c._ The =floor= of the third ventricle appears in a ventral view of the
brain (Fig. 138, Fig. 142) as a somewhat diamond-shaped space craniad of
the pedunculi cerebri (Fig. 142, _a_) and bounded along its cranial
margin by the =optic tracts= (Fig. 142, _d_). The optic tracts come from
the thalami, as already described; they converge and unite to form the
optic chiasma (Fig. 142, _e_), from which the optic nerves (_f_)
diverge.

Immediately caudad of the optic chiasma lies a considerable rounded gray
elevation, the =tuber cinereum= (Fig. 142, _h_). This bears on its
ventral surface in the natural condition the =infundibulum= (Fig. 138,
_d_) with the =hypophysis= (Fig. 138, _e_); in cases where the two
latter structures have been removed (Fig. 142) the tuber cinereum (_h_)
bears a small longitudinal opening (_i_) for attachment of the
infundibulum. The infundibulum (Fig. 138, _d_) is a hollow extension of
the floor of the third ventricle, and is attached to the middle of the
ventral surface of the tuber cinereum. It bears at its ventral end the
hypophysis (pituitary body) (Fig. 138, _e_), a vascular non-nervous body
of unknown function. The hypophysis is lodged in the sella turcica of
the sphenoid bone.

At its caudal border the tuber cinereum bears two white elevations, the
=mammillary bodies= (corpora mammillaria) (Fig. 142, _g_).

  [Illustration: FIG. 143.--LONGITUDINAL MEDIAN SECTION OF BRAIN.

  _I_, olfactory bulb; _II_, cerebrum; _III_, section of cerebellum,
  showing “arbor vitæ”; _IV_, medulla oblongata. _a_, tractus
  olfactorius; _b_, substantia perforata anterior; _c_, anterior
  commissure; _d_, lamina terminalis; _e_, optic chiasma; _f_, massa
  intermedia of thalamus; _g′_, infundibulum; _g_, hypophysis; _h_,
  third ventricle; _i_, mammillary body; _j_, aqueductus cerebri (or
  aqueduct of Sylvius); _k_, pons; _l_, velum medullare anterius; _m_,
  fourth ventricle; _n_, velum medullare posterius; _o_, continuation of
  canal of spinal cord; _p_, corpus callosum (body); _q_, genu of corpus
  callosum; _r_, rostrum; _s_, splenium; _t_, septum pellucidum; _u_,
  fornix; _v_, pillars of fornix; _w_, choroid plexus of third
  ventricle; _x_, stria medullaris; _y_, corpus pineale; _z_, cranial
  corpus quadrigeminum; _z′_, posterior commissure. 1, sulcus falcialis;
  2, sulcus cruciatus; 3, sulcus splenialis; 4, sulcus marginalis; 5,
  sulcus supracallosalis (or callosalis).]

The =third ventricle= (Fig. 143, _h_; Fig. 141, _v_) is a very narrow
slit-like space, of considerable extent dorsoventrally, but less than a
millimeter in width; it lies between the medial ends of the thalami
(Fig. 141), and extends ventrad into the tuber cinereum, and thence into
the infundibulum (Fig. 143, _g′_). Dorsad it extends into the corpus
pineale (Fig. 143, _y_). The third ventricle communicates caudally near
its dorsal border with the aqueductus cerebri (_j_); craniolaterally
with the lateral ventricles, through the =interventricular foramen=
(foramen of Monroe). Its cranial boundary forms in the middle line a
thin plate, the =lamina terminalis= (_d_), which is, morphologically,
the cranial termination of the cerebrospinal axis; it lies at the bottom
of the deep fissure between the cerebral hemispheres. At the dorsal
border of the lamina terminalis is a strong transverse band of fibres
connecting the two sides of the brain; this is the =anterior commissure=
(_c_). The cavity of the third ventricle is much encroached upon by the
meeting and secondary union of the two thalami across the middle line,
forming the massa intermedia (_f_).

The boundaries of the third ventricle, in order, are as follows,
beginning dorsocraniad of the communication with the aqueductus cerebri:
the posterior commissure (Fig. 143, _z′_), the pineal body (_y_), the
choroid plexus of the third ventricle (_w_), the columns of the fornix
(_v_), the anterior commissure (_c_), the lamina terminalis (_d_), the
tuber cinereum with the infundibulum (_g′_), the substantia perforata
posterior, and the midbrain. The lateral boundaries are formed by the
thalami (Fig. 141, _t_).


5. _Telencephalon._--The telencephalon includes the two cerebral
hemispheres. The name =cerebrum= is also applied to this portion of the
brain; frequently, however, the name cerebrum is used as signifying the
entire mass of the brain craniad of the rhombencephalon,--therefore
including mesencephalon, diencephalon, and telencephalon. The term will
here be used as synonymous with telencephalon.

The =cerebral hemispheres= arise as two lateral outgrowths from the
cranial end of the primitive forebrain. They have undergone great
increase in size in the course of evolution, so as to form the larger
part of the brain; at the same time important modifications of structure
have taken place. In the original condition the medial faces of the two
hemispheres are not connected, the two being separate outgrowths of the
’tween-brain, and connected only through the latter. But secondary
connections have been formed across the fissure between the two
hemispheres, resulting in the production of the =corpus callosum= (Fig.
143, _p_; Fig. 147; Figs. 149-152, _a_), a broad transverse band of
white fibres connecting the two hemispheres dorsad of the ’tween-brain.
Ventrad of the corpus callosum another secondary union has resulted in
the production of the =fornix= (Fig. 143, _u_).

  [Illustration: FIG. 144.--LATERAL SURFACE OF THE BRAIN.

  _a_, olfactory bulb; _b_, cerebral hemisphere; _c_, cerebellum; _d_,
  medulla oblongata; _e_, tractus olfactorius; _f_, lobus pyriformis or
  tractus postrhinalis; _g_, pons; _h_, trapezium; _i_, pyramid; _j_,
  area elliptica; _k_, area ovalis. _II_, N. opticus; _V_, N.
  trigeminus; _VII_, N. facialis; _VIII_, N. acusticus; _IX_, N.
  glossopharyngeus; _X_, N. vagus; _XI_, N. accessorius. 1. sulcus
  præsylvius; 2, sulcus cruciatus; 3, sulcus ansatus; 4, sulcus
  lateralis; 5, sulcus suprasylvius; 6, sulcus anterior; 7, sulcus
  posterior; 8, sulcus rhinalis; 9. fissura Sylvii; 10. sulcus rhinalis
  posterior.]

=External Features.=--With increase in size the mass of the cerebrum
shows externally a tendency to divide into three lobes, one craniad, the
=frontal= (Fig. 145, _A_); one caudoventrad, the =temporal= (_B_); and
one caudodorsad, the =occipital= (_C_). The two latter are not
distinctly marked off from one another. The limit between the temporal
and frontal lobes is marked by a short deep fissure, the =lateral
fissure= (=fissura cerebri lateralis=), or fissure of Sylvius (Fig.
144, 9; Fig. 145, _a_). Each lobe is thrown up into elevations or
=gyri=, which are separated by grooves or =sulci=; these are described
below. The homology of the cerebral gyri and sulci of the cat with those
of man is in most cases uncertain.

The sulci and gyri of the cerebral hemispheres may be described briefly
in their main features as follows: On the lateral surface of the
hemisphere (Fig. 145) the lateral fissure (fissura cerebri lateralis),
or fissure of Sylvius, separating temporal and frontal lobes, forms the
most convenient point of departure for an understanding of the fissures.
The fissure of Sylvius is short but deep, and is formed early during
development. In man it covers an area, the =insula=, at its bottom,
which may be seen by separating the sides of the fissure. In the cat the
insula is rudimentary and can be demonstrated only with difficulty.

The lateral surface of the hemisphere is marked by fissures which form
three concentric arches (_b_-_c_, _d_, and _e_), irregular and
incomplete, about the fissure of Sylvius. These arches all open ventrad.
The first arch (_b_-_c_) (that next to the fissure of Sylvius) lacks the
central part, the keystone, so that a complete arch is not formed, but
only the two sides of the arch, as two separate sulci (_b_ and _c_). The
one of these craniad of the fissure of Sylvius is the =sulcus anterior=
(_b_); the other is the =sulcus posterior= (_c_). In the dog this arch
is usually complete and the sulcus forming it is frequently known as the
ectosylvian sulcus (=sulcus ectosylvius=).

  [Illustration: FIG. 145.--DIAGRAM OF THE SULCI AND GYRI ON THE LATERAL
  SURFACE OF THE HEMISPHERE.

  _A_, frontal lobe; _B_, temporal lobe; _C_, occipital lobe. _a_,
  lateral fissure or fissure of Sylvius; _b_, sulcus anterior; _c_,
  sulcus posterior (the broken line connecting the ends of _a_ and _b_
  serves to show how the first arch is completed to form the ectosylvian
  sulcus, as in the dog); _d_, sulcus suprasylvius; _e_, sulcus
  lateralis; _f_, sulcus cruciatus; _g_, sulcus coronalis; _h_, sulcus
  ansatus; _i_, sulcus rhinalis; _j_, sulcus præsylvius; _k_, sulcus
  rhinalis posterior. 1, anterior Sylvian gyrus; 2, posterior Sylvian
  gyrus; 3, gyrus ectosylvius; 4, gyrus suprasylvius; 5, gyrus
  marginalis; 6, gyrus compositus posterior; 7, sigmoid gyrus; 8,
  olfactory tract; 9, orbital gyrus; 10, lobus pyriformis; 11, olfactory
  bulb.]

The gyri included between the fissure of Sylvius on the one hand and the
anterior and posterior sulci on the other are known as the =anterior=
(1) and =posterior= (2) =Sylvian gyri=.

The second arch is formed by the =suprasylvian sulcus= (=sulcus
suprasylvius=) (_d_). The gyrus between the anterior and posterior sulci
ventrad and the suprasylvian sulcus dorsad is the =ectosylvian gyrus=
(3) (because dorsad of the ectosylvian sulcus).

The third arched sulcus, next to the medial margin of the hemisphere, is
variable: it forms the =lateral sulcus= (_e_). The gyrus lying between
the suprasylvian and lateral sulci is the =suprasylvian gyrus= (4)
(because dorsad of the suprasylvian sulcus). The lateral sulcus is
sometimes broken into two (as in Fig. 137, _h_), the two ends
overlapping so as to leave a small gyrus between the two ends.

The gyrus dorsomediad of the lateral sulcus, extending onto the medial
surface of the hemisphere as far as the splenial sulcus, is the
=marginal gyrus= (5).

The four sets of gyri included between these three sets of arched sulci
and the fissure of Sylvius unite caudad and craniad to form single gyri.
The caudal one is the =gyrus compositus posterior= (6). The cranial one
(less regular than the caudal one) is the =sigmoid gyrus= (7). The
latter curves about the cruciate sulcus (_f_) (described below).

In the cranial part of the lateral surface of the hemisphere are certain
sulci and gyri which do not belong to the system above described. The
=cruciate sulcus= (_f_) is a short transverse sulcus passing from the
lateral surface of the hemisphere onto its medial surface, where it
extends caudad about a centimeter. Curving around the lateral end of
this, separated from it by part of the sigmoid gyrus, is the short
=coronal sulcus= (_g_). Connected usually with the end of the lateral
sulcus (_e_) and running nearly parallel with the cruciate sulcus is the
short =sulcus ansatus= (_h_).

At its ventral end the fissure of Sylvius (_a_) joins a longitudinal
groove passing craniad and caudad from the point of junction. That part
which passes craniad is the =sulcus rhinalis= (_i_); it forms the
dorsolateral boundary of the olfactory tract (8). Passing dorsocraniad
from the sulcus rhinalis is a sulcus which separates a very small
cranial lobe from the rest of the hemisphere; this is the =supraorbital=
or =præsylvian sulcus= (_j_). The portion of the hemisphere craniad of
this sulcus is the =orbital gyrus= (9).

The sulcus rhinalis (_i_) is continuous caudad with the =sulcus rhinalis
posterior= (or =sulcus postrhinalis=) (_k_). This extends caudad onto
that portion of the hemisphere which faces the cerebellum. It forms the
lateral boundary of a large elongated oval lobe lying at the side of the
ventral floor of the midbrain and ’tween-brain. This lobe has been
called =tractus postrhinalis= or =lobus pyriformis= (Fig. 145, 10; Fig.
138, _f_).

In addition to the sulci and gyri above mentioned, any given specimen
will usually show a number of small inconstant sulci and gyri in various
regions; these inconstant structures will not be here described.

  [Illustration: FIG. 146.--DIAGRAM OF THE SULCI AND GYRI ON THE MEDIAL
  SURFACE OF THE HEMISPHERE.

  _a_, sulcus splenialis; _b_, sulcus marginalis; _c_, sulcus cruciatus;
  _d_, sulcus falcialis; _e_, sulcus supracallosalis; _f_, sulcus
  rhinalis posterior; _g_, hippocampal sulcus; _h_, corpus callosum. 1,
  gyrus marginalis; 2, gyrus fornicatus; 3, gyrus compositus posterior.]

On the medial surface of the hemisphere (Fig. 146), the following
arrangement of sulci and gyri seems to be typical. Some distance from
the dorsal margin a long sulcus runs parallel with the margin; this is
the =sulcus splenialis= (_a_). The =marginal gyrus= (1) is dorsad of the
splenial sulcus, passing onto the lateral surface of the hemisphere,
where it is bounded by the lateral sulcus. The splenial sulcus extends
onto the caudal surface of the hemisphere. A shallow =sulcus marginalis=
(_b_) occurs frequently between the sulcus splenialis and the dorsal
margin of the hemisphere. Cranioventrad or the cranial end of the
splenial sulcus is that portion of the =sulcus cruciatus= (_c_) that
lies on the medial surface of the hemisphere. Ventrad of this is a short
shallow furrow which has been called the =sulcus falcialis= (_d_).

Immediately dorsad of the corpus callosum (_h_), separating its dorsal
surface from a part of the hemisphere, is the =supracallosal= or
=callosal= sulcus (_e_). Between the supracallosal (_e_) and splenial
(_a_) sulci is the =gyrus fornicatus= (2).

On the caudal surface of the hemisphere (that facing the cerebellum)
appear the ends of the sulcus splenialis (_a_) and the sulcus rhinalis
posterior (_f_). Hidden in the natural condition by the thalami and
optic tract is the broad =hippocampal= sulcus (_g_), marking externally
the course of the hippocampus.

A further extension of the surface of the cerebrum has taken place in
connection with the sense of smell. A mass of gray matter, the
=olfactory bulb= (Fig. 144, _a_), reckoned as a part of the cerebrum, is
separated from the latter and lies against the cribriform plate of the
ethmoid bone. From it the olfactory fibres pass through the perforations
of the plate to the olfactory mucous membrane. The olfactory bulb
contains a cavity, a part of the lateral ventricle.

The bulb lies against the ventral surface of the frontal lobe and
projects craniad of it. It is connected to the cerebrum by a tract of
fibres, the =olfactory tract= (Fig. 138, _a_), which is divisible into
two roots, medial and lateral. The medial root comes from the medial
surface of the frontal lobe, where it is continuous with a tract
extending to the cranial end of the corpus callosum. The lateral root is
traceable from an elevated gyrus-like portion of the cerebrum which lies
at the side of the infundibulum and is known as the lobus pyriformis or
tractus postrhinalis (Fig. 138, _f_). The lateral root is divisible into
a medial white strand and a lateral gray strand.

That part of the brain comprising the olfactory bulb and the parts
intimately related to it are frequently included under the term
=rhinencephalon=.

In the triangular area between the two olfactory tracts and craniad of
the optic chiasma appears a mass of gray matter, subdivided by a
longitudinal fissure. This possesses numerous openings through which
blood-vessels pass to the brain substance, and is thence known as the
=anterior perforated substance= (=substantia perforata anterior=) (Fig.
138, _b_).

=Internal Structures of the Cerebrum.=--The cavity of each of the
cerebral hemispheres is known as a =lateral ventricle=. The two lateral
ventricles constitute the _first_ and _second_ of the ventricles of the
brain, whence the application of the names _third_ and _fourth_
ventricles to the cavities of the ’tween-brain and hindbrain. The
lateral ventricles do not grow at the same rate as the walls of the
hemispheres, so that they remain comparatively small. The cavity of
each ventricle is further reduced in size by the development on its
floor of a large ridge-like thickening, the =corpus striatum= (Fig. 148,
_f_).

The dorsal wall or roof of the lateral ventricle joins the thin roof of
the third ventricle on each side along an oblique curved line (Fig. 141,
1) which follows the cranial or lateral border of the thalamus (Fig.
141, _t_). Along this line the thin roof of the brain is folded in
together with the pia mater to form the =choroid plexus= of the =lateral
ventricles= (=lamina chorioidea epithelialis=) (Fig. 148, _e_). When
this is pulled out there is left a fissure, the “great transverse
fissure of the cerebrum” (Fig. 141, 1). Just dorsad of the groove
between the thalami there runs a tract of white fibres known as the
=fornix= (Fig. 148, _a_). The two halves of the fornix separate at the
cranial ends of the thalami and pass ventrad, forming thus the =pillars=
of the =fornix= (Fig. 148, _b_; Fig. 143, _v_). Dorsad of the cranial
end of the fornix the =corpus callosum= (Fig. 143, _p_) passes from one
hemisphere to the other. Caudad of the pillars of the fornix, the
lateral ventricles communicate with the third ventricle by way of the
=interventricular foramen= (foramen of Monroe).

The parts of the cerebrum may now be taken up in detail.

  [Illustration: FIG. 147.--THE CORPUS CALLOSUM.

  The dorsal portion of the hemispheres has been dissected away, then
  sliced off, showing the plate of transverse fibres forming the corpus
  callosum. _a_, splenium; _b_, genu; _c_, line marking the medial edge
  of the hemispheres; _d_, line marking the lateral boundary of the
  supracallosal sulcus; laterad of this line the corpus callosum lies in
  the substance of the hemispheres, which have been dissected away; _e_,
  line marking medial limit of cut surface.]

The =corpus callosum= (Fig. 147; Fig. 143, _p_; Figs. 149-152, _a_) is a
broad transverse band of fibres forming a secondary connection between
the medial walls of the two hemispheres, dorsad of the roof of the third
ventricle. Its outer surface (Fig. 147) is exposed at the bottom of the
fissure which separates the hemispheres. On each side it passes laterad,
forming the roof of the lateral ventricle. Its cranial part lies dorsad
of the corpus striatum, and its caudal part dorsad of the thalamus.
Laterally its fibres radiate into the substance of the hemispheres. At
its cranial end the corpus callosum bends ventrad and then caudad (Fig.
143). The part which turns to pass ventrad is the =genu= (Fig. 143, _q_)
or knee, while the part which projects caudad is the =rostrum= (_r_).
The caudal border of the corpus callosum is also thickened and turned
ventrad and is called the =splenium= (Fig. 143, _s_); it lies dorsad of
the cranial corpora quadrigemina (_z_). The caudal half of the ventral
surface of the corpus callosum is united with the fornix (Fig. 143,
_u_).

  [Illustration: FIG. 148.--FORNIX, HIPPOCAMPUS, AND CORPUS STRIATUM.

  The dorsal portion of the hemispheres has been dissected away and the
  corpus callosum removed. _a_, fornix; _b_, columns or pillars of the
  fornix; _c_, crura of the fornix; _d_, hippocampus; _e_, choroid
  plexus of the lateral ventricles overlying the fimbria (the choroid
  plexus shows an artery); _f_, corpus striatum; _g_, corpora
  quadrigemina; _h_, position of the interventricular foramen (foramen
  of Monroe).]

The =fornix= (Fig. 148, _a_; Fig. 143, _u_, _v_; Figs. 150-152, _b_)
consists of an arched tract of longitudinal fibres near the medial
border of each hemisphere, ventrad of the corpus callosum. Each tract
begins in the mammillary bodies, and passes dorsad, the two converging
until they run side by side, forming a cylindrical dorsoventral bundle
known as the columns or pillars of the fornix (Fig. 143, _v_; Fig. 150,
_e_), which cross the anterior commissure (Fig. 143, _c_; Fig. 150, _f_)
caudad of the latter. Caudad of the pillars of the fornix, between these
and the thalamus, lies on each side the interventricular foramen or
foramen of Monroe, a small opening which connects the lateral ventricles
with the third ventricle. Dorsad of the foramen the fornix turns caudad,
the two fibre-tracts of each hemisphere lying side by side and closely
connected (Fig. 148, _a_), forming thus another secondary union between
the medial surfaces of the two hemispheres. This portion of the fornix
is the =corpus= or =body= (Fig. 148, _a_); it lies dorsad of the roof of
the third ventricle and passes to the splenium (Fig. 143, _s_) of the
corpus callosum, and its dorsal surface unites with the ventral surface
of the latter (Fig. 143). Caudad the two halves of the fornix diverge,
forming the =crura= of the fornix (Fig. 148, _c_); these and the body
are continuous laterally with the =hippocampus= (Fig. 148, _d_) and the
=fimbria= (Fig. 148, beneath _e_).

The =anterior commissure= (Fig. 143, _c_; Fig. 150, _f_) is a transverse
band of white fibres which stretches from one hemisphere to the other
about half way between the interventricular foramen or foramen of Monroe
and the floor of the third ventricle, and just craniad of the pillars of
the fornix. This tract of fibres is developed in the original wall of
the third ventricle, so that it does not form a _secondary_ connection
between the halves of the cerebrum, as do the fornix and corpus
callosum. It lies dorsad of the lamina terminalis (Fig. 143, _d_) and
is continuous with it.

The =septum pellucidum= (Fig. 143, _t_) is a vertical partition which
separates the lateral ventricles and fills the interval between the
corpus callosum dorsad and the fornix ventrad. It is triangular and
translucent. It is formed from the medial walls of the two hemispheres
and therefore is made up of two laminæ which embrace between them a
space which originally was a part of the fissure separating the
hemispheres. This space has been called the fifth ventricle.

  [Illustration: FIG. 149.--CAUDAL SURFACE OF TRANSVERSE SECTION OF
  BRAIN THROUGH THE GENU OF THE CORPUS CALLOSUM.

  FIG. 150.--CAUDAL SURFACE OF TRANSVERSE SECTION OF BRAIN THROUGH THE
  OPTIC CHIASMA AND THE REGION OF THE INTERVENTRICULAR FORAMEN (FORAMEN
  OF MONROE).

  Fig. 149.--Gray matter dotted; white matter with a few lines. 1, right
  hemisphere; 2, left hemisphere. _a_, corpus callosum, section through
  genu and rostrum; _b_, cavity of lateral ventricles.

  Fig. 150.--1, right hemisphere; 2, left hemisphere. _a_, corpus
  callosum; _b_, fornix (cut); _c_, cavity of lateral ventricles; _d_,
  fimbria (_d′_, cut surface; _d_, caudal uncut surface of the part that
  curves ventrad); _e_, pillars of fornix; _f_, anterior commissure;
  _g_, parts of third ventricle; _h_, optic chiasma; _i_, parts of
  corpus striatum.]

  [Illustration: FIG. 151.--CAUDAL SURFACE OF TRANSVERSE SECTION OF THE
  BRAIN THROUGH THE TUBER CINEREUM AND INFUNDIBULUM, CRANIAD OF THE
  HYPOPHYSIS.

  _a_, corpus callosum; _b_, fornix (continuous at the sides with the
  hippocampus); _c_, cavity of lateral ventricles; _d_, hippocampus;
  _e_, choroid plexus of the third ventricle (roof of the diencephalon);
  _f_, dorsal part of cavity of the third ventricle; _g_, section of
  thalamus; _h_, massa intermedia of the thalami, dividing the third
  ventricle into a dorsal (_f_) and a ventral (_i_) portion; _i_,
  ventral part of third ventricle; _j_, part of optic tracts; _k_, thin
  wall of infundibulum, with part of cavity of third ventricle; _l_,
  line separating roof of thalamus (diencephalon) from floor of
  hemispheres (telencephalon).]

The =hippocampus= (Fig. 148, _d_; Fig. 152, _d_) is an elongated rounded
elevation of the floor of the lateral ventricle. It is continuous mediad
with the fornix (Fig. 148, _a_) and extends thence along the inferior
horn of the lateral ventricle to its end in the temporal lobe. It is
somewhat narrower at its lateral end. It is thus curved into a
semicircle in conformity with the inferior horn of the ventricle. Its
dorsal surface is convex and looks into the lateral ventricle; its
ventral surface is concave and rests upon the thalamus and the optic
tract. Along the craniolateral edge of the hippocampus is a broad,
clearly marked fibre-tract, the =fimbria=; this runs parallel to the
choroid plexus of the lateral ventricle and beneath it, and is
continuous at its medial end with the fornix.

The =corpus striatum= (Fig. 148, _f_; Fig. 141, _y_; Fig. 150, _i_) is a
fusiform or ovoid elevation of the floor of the lateral ventricle. One
of its narrow ends lies about opposite the middle of the thalamus (Fig.
141, _t_) and it extends thence obliquely mediad nearly parallel with
the thalamus. In the groove between it and the thalamus is the choroid
plexus of the lateral ventricles (Fig. 148, _e_). Internally the corpus
striatum is made up of several layers of different texture (Fig. 150,
_i_), whence its name.

  [Illustration: FIG. 152.--CAUDAL SURFACE OF TRANSVERSE SECTION OF THE
  BRAIN THROUGH THE PINEAL BODY AND THALAMI.

  FIG. 153.--CAUDAL SURFACE OF TRANSVERSE SECTION OF THE BRAIN THROUGH
  THE CRANIAL PAIR OF CORPORA QUADRIGEMINA.

  Fig. 152.--_a_, corpus callosum; _b_, fornix; _c_, inferior horn of
  lateral ventricles; _d_, hippocampus; _e_, thalamus; _f_, third
  ventricle; _g_, pineal body; _h_, space between the floor of the
  hemisphere (hippocampus) and roof of the ’tween-brain (thalamus).

  Fig. 153.--_a_, cranial corpora quadrigemina; _b_, hippocampus; _c_,
  part of inferior horn of lateral ventricle; _d_, aqueductus cerebri
  (aqueduct of Sylvius); _e_, space between the outer surface of the
  midbrain and the lower surface of the hemisphere; _f_, cross-section
  of midbrain; _g_, pedunculi cerebri.]

The =choroid plexus= of the lateral ventricles (=lamina chorioidea
epithelialis=) (Fig. 148, _e_).--The line of junction of the roof of the
third ventricle (i.e., the choroid plexus of the third ventricle) and
the cerebral hemispheres is along the lateral (or cranial) border of the
thalamus (Fig. 141, _t_). Along this line (Fig. 141, 1) the brain-wall
remains very thin and becomes closely associated with the pia mater, so
that on the removal of the pia there is left the “transverse fissure”
which leads into the lateral ventricle. In an early stage, before the
cerebrum has grown far caudad, the fissure is exposed in dorsal view,
but after the hemispheres have covered the thalami the fissure appears
to be in the lower face of the hemisphere. Through this fissure the pia
mater extends upward into the lateral ventricles as a fold separated
from the ventricle by the thin brain-wall. This fold is vascular and is
known as the choroid plexus of the lateral ventricle (Fig. 148, _e_). It
is a fringe-like fold lying on the fimbria and extending from the
foramen of Monroe (at _h_) nearly to the end of the inferior horn of the
lateral ventricle.

The =lateral ventricles= are the extensions into the hemispheres of the
originally unpaired cavity of the forebrain. Each consists of a portion
parallel to the basis cranii and lying at the side of the septum
pellucidum between the corpus callosum dorsad and the corpus striatum,
hippocampus, and fornix ventrad, and of two horns, an =anterior= and an
=inferior= horn. The inferior horn (Fig. 152, _c_) is a narrow cleft,
crescent-shaped in cross-section, which follows the dorsal surface of
the hippocampus (Fig. 148, _d_; Fig. 152, _d_) along the temporal lobe
to its end almost against the tuber cinereum. It thus passes first
caudad and then ventrad and finally mediad. The choroid plexus and
hippocampus project into it from its floor. The =anterior= horn extends
ventrad and then slightly caudad in the frontal lobe, following the
corpus striatum (Fig. 148, _f_), on which it lies.

The =interventricular foramen= (or =foramen of Monroe=).--If the choroid
plexus of the lateral ventricle (Fig. 148, _e_) is followed to its
medial end, it is found to pass through a foramen (at _h_) in which it
becomes continuous with the opposite plexus or roof of the third
ventricle. This foramen leads from one lateral ventricle to the other
and is connected ventrally by a median opening with the third ventricle.
It is thus Y-shaped or T-shaped and is the interventricular foramen (or
foramen of Monroe). The foramen lies opposite the middle of the corpus
striatum and caudad of the pillars of the fornix.

=Membranes of the Brain.=--The membranes of the brain are the =dura
mater=, the =arachnoid=, and the =pia mater=.

The dura mater is a strong fibrous membrane lining the cranial cavity
and covering the brain. It is strongly attached to the projections of
the base of the skull and to the tentorium. It dips between the cerebral
hemispheres and olfactory bulbs, forming the =falx cerebri=. It likewise
dips between the cerebrum and the cerebellum, covering both surfaces of
the bony tentorium. The dura mater does not pass into the fissures or
sulci of the surface of the brain. It becomes continuous with the sheath
of the cranial nerves as they leave the skull. It is continuous with the
dura mater of the spinal cord.

The arachnoid and pia mater are essentially similar to the same
structures on the spinal cord. The pia mater dips into the fissures and
sulci of the brain.


II. THE PERIPHERAL NERVOUS SYSTEM.


1. =Cranial Nerves. Nervi cerebrales.=--I. N. OLFACTORIUS.--The
fasciculi of the olfactory nerves arise from the olfactory bulb (Fig.
144, _a_) and pass through the foramina of the cribriform plate, upon
which the bulb lies, to be distributed to the olfactory mucous membrane
of the nose.


II. N. OPTICUS.--The second nerve or optic (Fig. 138, _II_) arises from
the optic chiasma (Fig. 138, _c_), passes through the optic foramen, and
extends in an S-shaped curve to the eyeball. Its course is craniodorsad.
It pierces the sclerotic and choroid coats of the eye and spreads out
into the retina.


III. N. OCULOMOTORIUS.--The third or oculomotor nerve arises (Fig. 138,
_III_) from the pedunculus cerebri and passes into the orbit through the
orbital fissure. It passes between the lateral and superior recti, sends
a large branch to the superior rectus, supplies the medial rectus and
the retractor oculi, passes laterad of the optic nerve and supplies the
inferior rectus, and sends a long branch to the inferior oblique (Fig.
166, _f_). At the point where the branch is given off to the inferior
oblique muscle is the triangular reddish =ciliary= (or ophthalmic)
=ganglion=, about two millimeters in diameter. It is directly attached
to the inferior oblique branch of the third nerve and receives a
delicate sensory filament from the ophthalmic nerve. From the ciliary
ganglion proceed two =short ciliary nerves= which pass along each side
of the optic nerve to the eyeball. These nerves penetrate the sclerotic
at the sides of the eyeball to be distributed to the ball.


IV. N. TROCHLEARIS.--The fourth nerve, the trochlearis (or patheticus),
arises from the lateral border of the velum medullare anterius, as
already described (Fig. 141, _n_). It passes craniad, emerges through
the orbital fissure in company with the oculomotor, abducens, and
ophthalmic, passes dorsad of the superior rectus muscle, and reaches
(Fig. 154, _l_) the caudal border of the belly of the superior oblique
muscle near its middle. It supplies only the superior oblique.


V. N. TRIGEMINUS.--The fifth nerve, the trigeminus (or trifacial) arises
(Fig. 138, _V_) by two roots, a large sensory and a small motor root
(4), as already described (p. 347). One of these, the motor (4), is
smaller and more ventral; the other, the sensory root, is larger and
dorsal. The dorsal root soon enlarges to form a large ganglion, the
=semilunar= (or Gasserian) =ganglion= (Fig. 138, _k_), from which three
branches diverge. One branch is joined by the ventral root (4), which
passes over the ventral surface of the semilunar ganglion; and the nerve
thus formed is the =mandibular= division (1) of the fifth nerve. Of the
other two branches from the ganglion, the middle and longest is the
=maxillary= nerve (2), and the smallest is the =ophthalmic= (3). The
mandibular nerve is thus mixed, motor and sensory, while the others are
sensory.

1. =N. ophthalmicus.=--The ophthalmic or first division of the fifth
nerve arises from the semilunar (or Gasserian) ganglion. It passes out
of the cranial cavity and into the orbit by way of the orbital fissure,
in company with the third, fourth, and sixth nerves and with the
extension of the carotid (arterial) plexus.

It passes between the superior and medial recti along with the third
nerve, crosses dorsad of the optic nerve, and divides into
=infratrochlear= and =ethmoidal= branches. In the orbital fissure it
gives off the =frontal= nerve, and while crossing the optic it gives off
the =long ciliary= nerve.

_a._ =N. frontalis.=--The frontal nerve passes along the lateral border
of the superior oblique muscle and then laterad of the pulley to near
the middle of the supraorbital crest of the frontal bone. Here it passes
out of the orbit and is distributed to the integument of the upper
eyelid and the adjacent region at the side of the nose.

_b._ =N. infratrochlearis.=--The infratrochlear nerve passes between the
superior rectus and the superior oblique in the first part of its
course. It then passes ventrad of the superior oblique and ventrad of
the pulley to be distributed to the integument of the upper eyelid near
the inner angle.

_c._ =N. ethmoidalis.=--The ethmoidal nerve passes along with the
ethmoidal artery through the ethmoidal foramen (or foramina) in the
orbital plate of the frontal bone. It is finally distributed to the
mucosa of the nose and to the cartilage and integument of the snout.

_d._ =N. ciliaris longus.=--The long ciliary nerve arises from the
ophthalmic and passes along the optic nerve to be distributed to the
eyeball. It divides into several branches before penetrating the
sclerotic.

One or two small communicating branches to the =ciliary ganglion= are
given off at about the same point as the long ciliary nerve. (For a
description of this ganglion see the account of the oculomotor nerve,
page 369.)

2. =N. maxillaris.=--The maxillary nerve, the second division of N.
trigeminus, rises from the semilunar (Gasserian) ganglion and leaves the
skull by the foramen rotundum. It is the sensory nerve of the palate,
upper teeth and upper lip, and of part of the forehead and cheek.

On leaving the foramen the maxillary nerve divides into three branches,
the two =infraorbital= nerves (Fig. 154, _f_) and the =sphenopalatine=
(Fig. 154, _g_). Two smaller branches are likewise given off either
within or just outside of the foramen, the =lachrymal= nerve (Fig. 154,
_j_) and the =zygomatic= (subcutaneus malæ) (Fig. 154, _i_).

_a._ =N. lachrymalis= (Fig. 154, _j_; Fig. 155, _m_).--The lachrymal
nerve passes along the periorbita to the lachrymal gland (Fig. 154, 11),
to which it gives branches. It then continues caudad of the zygomatic
process of the temporal to the integument; here it turns caudad and is
distributed to the integument in the region between the eye and the
external ear (Fig. 155, _m_). It anastomoses with the zygomatic branch
of the seventh nerve (Fig. 155, _h_).

_b._ =N. zygomaticus= (subcutaneus malæ) (Fig. 154, _i_).--This arises
with the preceding and follows it for some distance. It passes through a
foramen in the frontal process of the malar bone and is distributed to
the lower eyelid and adjacent integument.

_c._ =Nn. infraorbitales= (Fig. 154, _f_; Fig. 155, _l_).--The
infraorbital nerves are two of nearly equal size. They pass through the
orbit ventrad of the eyeball to the infraorbital canal. On their course
each divides once or twice and each divides again in the infraorbital
foramen, so that about eight branches emerge from the infraorbital
foramen and diverge to the integument and whiskers of the upper lip and
to the side and wing of the nose (Fig. 155, _l_). In the infraorbital
canal, and before reaching it, branches are given to the molar teeth,
and a branch continues in the bone to the canine, incisor, and premolar
teeth.

_d._ =N. sphenopalatinus= (Fig. 154, _g_).--The sphenopalatine nerve
turns mediad from the infraorbitals, directing its course toward the
sphenopalatine foramen. Before reaching this it gives off the =greater
palatine= nerve (=N. palatinus major=), which enters the posterior
palatine canal and passes to the hard palate. The sphenopalatine then
usually divides into two branches which pass along side by side to enter
the =sphenopalatine ganglion=. This is a large elongated triangular
ganglion lying on the dorsal surface of the external pterygoid muscle,
just laterad of the sphenopalatine foramen.

The following nerves are connected with the sphenopalatine ganglion:

_a._ =N. palatinus minor.=--This leaves the craniolateral angle of the
ganglion and passes to the soft palate.

_b._ =N. nasalis posterior.=--The posterior nasal nerve enters the nasal
cavity by the sphenopalatine foramen and is distributed to the mucosa of
the ventral and middle parts of the nasal cavity.

_c._ =N. canalis pterygoidii= (Vidian Nerve).--This is a large nerve
which leaves the caudal angle of the sphenopalatine ganglion and passes
caudad. It enters the orbital fissure, lying in a groove on its ventral
wall (the cranial end of this groove is sometimes converted into a
canal). The groove ends caudally in a foramen which pierces the sphenoid
bone between the wing and the body and lies just mediad of the foramen
rotundum. The groove and foramen constitute the pterygoid canal (from
which the nerve is named). After emerging from the pterygoid canal onto
the ventral surface of the basisphenoid the nerve enters the tympanic
bulla along with the Eustachian tube, lying on the medial side of the
latter. Just after entering, on reaching the internal carotid artery, it
divides into two. One of these, =N. petrosus superficialis major= (p.
375), passes into the hiatus facialis of the petrous bone and joins the
facial nerve. The other, =N. petrosus profundus=, accompanies the
internal carotid artery caudad, turning therefore out of the bulla and
passing caudad along its medial side; it finally joins the superior
cervical ganglion of the sympathetic system.

3. =N. mandibularis.=--The third division of the fifth, the mandibular
nerve, takes origin by a strong root from the semilunar (or Gasserian)
ganglion, and receives also after separating from the ganglion the
smaller ventral root (portio minor) of the fifth nerve. The root from
the ganglion is sensory; the smaller root is motor, so that the
mandibular nerve is both sensory and motor. The nerve passes through the
foramen ovale, and sends off at once the following branches:

_a._ =N. auriculotemporalis= (Figs. 154 and 155, _n_).--This passes
dorsad between the cartilaginous auditory meatus and the zygomatic
process of the temporal bone (Fig. 154, _n_), emerges at the caudal
border of the masseter muscle (Fig. 155, _n_), and divides into two
chief branches. One, the =auricular= branch, passes along the cranial
side of the external ear and is distributed to its integument. The
other, the =temporal= branch, passes along the zygomatic arch, gives
branches to the temporal muscle and to the skin, follows the zygomatic
arch almost to the angle of the mouth, and anastomoses with the superior
buccal branch of the facial (Fig. 155, _k_).

_b._ =N. temporalis profundus.=--One or more large branches passing
mediad of the zygomatic arch to the temporal muscle.

_c._ =N. massetericus.=--The masseteric nerve passes dorsocraniad to the
masseter muscle.

_d._ =N. pterygoideus.=--One or more pterygoid branches pass to the
pterygoid muscles. A small twig from the nerve to the internal pterygoid
passes into the tympanic cavity and supplies the tensor tympani muscle.

_e._ =N. buccinatorius= (Fig. 154, _e_).--This passes craniad along the
dorsolateral surface of the pterygoid muscles (Fig. 154, 8) to the angle
of the mouth. Here it divides into branches to the masseter muscle, the
mucosa of the mouth, and to the lips.

  [Illustration: FIG. 154.--DISSECTION SHOWING A NUMBER OF THE CRANIAL
  NERVES.

  The mandible and zygomatic arch have been cut and removed; the
  temporal and internal pterygoid muscles are also removed. _a_, N.
  hypoglossus; _b_, N. lingualis; _c_, N. chorda tympani; _d_, N.
  alveolaris inferior (cut); _e_, N. buccinatorius; _f_, Nn.
  infraorbitales; _g_, N. sphenopalatinus; _h_, branch of N.
  oculomotorius; _i_, N. zygomaticus; _j_, N. lachrymalis; _k_, N.
  abducens; _l_, N. trochlearis; _m_, N. frontalis; _n_, N.
  auriculotemporalis. 1, cut end of zygomatic process of temporal; 2,
  tympanic bulla; 3, M. digastricus; 4, M. constrictor pharyngis medius;
  5, M. hyoglossus; 6, M. genioglossus; 7, M. geniohyoideus; 8, M.
  pterygoideus externus (cut); 9, cut cranial end of zygomatic arch; 10,
  mandible (cut); 11, lachrymal gland.]

After giving off the above branches the mandibular nerve passes three or
four millimeters laterad along the root of the zygomatic process of the
temporal bone, and divides into two large branches, the =inferior
alveolar= (or dental) nerve (_d_) and the =lingual= nerve (_b_).

_f._ =N. alveolaris inferior= (Fig. 154, _d_).--This passes toward the
mandibular foramen, but before reaching it gives off a branch to the
mylohyoid and digastric muscles. It then enters the foramen, passes
through the mandibular canal, and gives numerous =inferior dental=
branches to the teeth. At the mental foramen (or foramina) it passes out
of the canal and divides into several =mental= nerves, to the chin,
lower lip, and mucosa of the lower jaw.

_g._ =N. lingualis= (Fig. 154, _b_).--The lingual nerve passes between
the internal and external pterygoid muscles, and two or three
millimeters from its origin it receives the =chorda tympani= nerve
(_c_), a communicating branch from the facial (see page 376). It passes
onto the ventral surface of the external pterygoid, thence onto the side
of the tongue, beneath the mylohyoid. On the side of the tongue it
divides into branches which enter the tongue and are distributed to its
mucous membrane. One branch passes to the mucosa of the pharynx. Just
before entering the tongue a branch is given off to the sublingual and
submaxillary glands.


VI. N. ABDUCENS.--The sixth nerve, the abducens, arises from the
medulla, as already described (Fig. 138, _VI_, and page 347). It passes
into the orbit through the orbital fissure, then extends obliquely
cranioventrad along the medial surface of the lateral rectus muscle
(Fig. 154, _k_). At about the middle of the length of the muscle it
divides into two or three branches which enter at once into the lateral
rectus and supply it.


VII. N. FACIALIS (Fig. 155).--The seventh or facial nerve arises from
the trapezium at the caudal margin of the pons, craniad of the origin of
the eighth nerve, as described in the account of the brain (Fig. 138,
_VII_). It passes into the internal auditory meatus, traverses the
facial canal through the petrous bone, and emerges at the stylomastoid
foramen.

Within the facial canal the nerve bears an enlargement, the =ganglion
geniculi=. It gives off within the canal a branch to the stapedius
muscle, and the =superficial petrosal= and =chorda tympani= nerves.

The =superficial petrosal= (N. petrosus superficialis major) nerve
passes into the hiatus facialis, through the canal which forms its
continuation, and joins the sphenopalatine ganglion (p. 373).

  [Illustration: FIG. 155.--SUPERFICIAL NERVES OF THE FACE.

  _a_, N. facialis; _b_, branch to digastric; _c_, N. auricularis
  posterior; _d_, branch to inside of ear; _e_, ventral ramus; _f_,
  dorsal ramus; _g_, temporal nerve; _h_, zygomatic nerve; _i_, nerve to
  stylohyoid muscle; _j_, inferior buccal nerve; _k_, superior buccal
  nerve; _l_, infraorbital branches of fifth nerve; _m_, lachrymal
  branches of fifth nerve; _n_, auriculotemporal branches of fifth
  nerve. 1, M. digastricus; 2, M. stylohyoideus; 3, M. masseter.]

The =chorda tympani= is given off two or three millimeters before the
emergence of the facial at the stylomastoid foramen. It passes into the
tympanic cavity, extends across it between the malleus and incus,
passing close against the tensor tympani muscle, and leaves it (by a
small cleft, the canal of Huguier) between the bulla and the squamous
portion of the temporal. It then passes craniad (Fig. 154, _c_), ventrad
of the root of the zygomatic process of the temporal, and joins the
lingual nerve (Fig. 154, _b_) (branch of the third division of the fifth
nerve).

On emerging from the stylomastoid foramen the facial nerve (Fig. 155,
_a_) gives off at once a small branch (_b_) to the digastric muscle (1),
and a larger branch, =N. auricularis posterior= (_c_), which passes
dorsocaudad about the base of the ear, supplying some of its muscles.
Another small branch (_d_) pierces the cartilaginous external ear and is
distributed to its inner surface. The facial nerve then curves craniad
about the proximal part of the cartilaginous external ear, and divides
five or six millimeters from its emergence into two main branches, which
may be designated as the =dorsal= (_f_) and =ventral= (_e_) rami. A
third small branch may also rise from the point of union of the two; it
is usually, however, a twig from the dorsal ramus, and passes to M.
submentalis.

The dorsal ramus (_f_) sends two or three small branches to the cheek
(including the one just mentioned), and divides into the =temporal=
(_g_) and the =zygomatic= (_h_) branches. The former (_g_) passes along
the cranial margin of the external ear, supplying the superficial
muscles, and extends into the temporal region, where it lies deeper than
the terminal branches of the lachrymal nerve (_m_) (from the fifth
cranial). The =zygomatic= branch (_h_) passes across the malar bone to
the caudal angle of the eye, sends branches into both eyelids,
anastomoses with twigs from the lachrymal branch (_m_) of the fifth
nerve, and passes along the medial side of the eye to the lateral
surface of the nose, where it ramifies.

The ventral ramus (_e_) gives off a minute branch (_i_) to the
stylohyoid muscle (2), then proceeds toward the angle of the mouth and
divides into =superior= (_k_) and =inferior= (_j_) buccal branches, the
former to the muscles of the upper lip and the contiguous regions, the
latter to those of the lower lip and chin.

The seventh nerve thus supplies most of the muscles of the head except
those of mastication, and of these it supplies the digastric.


VIII. N. ACUSTICUS.--The eighth or auditory nerve takes origin (Fig.
138, _VIII_) from the floor of the fourth ventricle, as before described
(page 347). It passes into the internal auditory meatus and is
distributed to the internal ear within the petrous bone.


IX. N. GLOSSOPHARYNGEUS (Fig. 156, _a_).--The ninth or glossopharyngeal
nerve takes origin (Fig. 138, _IX_) from the side of the medulla, as
described in the account of the brain. Close to its origin its trunk
bears a small enlargement, the =ganglion superius=. It passes along with
the tenth and eleventh nerves through the jugular foramen. At its exit
it has a ganglionic enlargement, the =ganglion petrosum=; this is
connected by fine fibres with the ganglion nodosum (Fig. 156, _d_) of
the vagus. The glossopharyngeal (Fig. 156, _a_) then passes craniad over
the surface of the tympanic bulla (15) and mediad of the digastric
muscle. It continues mediad of the carotid artery, and as it approaches
the cranial cornu of the hyoid divides into two portions, one of which
passes to the muscles and mucosa of the pharynx, and the other to the
tongue, where it is the special nerve of taste.


X. N. VAGUS.--The vagus nerve arises from the side of the medulla in the
manner described under the Brain (page 346 and Fig. 138, _X_). It passes
through the jugular foramen along with the glossopharyngeal and
accessory nerves.

=Cervical Portion of the Vagus= (Fig. 156, _d_, _d′_).--In the foramen,
or just before entering it, it presents a ganglionic enlargement, the
=ganglion jugulare= (or “ganglion of the root”), and a short distance
beyond the foramen it forms a second ganglion, the =ganglion nodosum=
(_d_) (or “ganglion of the trunk”), which lies dorsocaudad of the
superior cervical sympathetic ganglion (_e_). The ganglia of the vagus
and sympathetic are closely bound together by connective tissue, and
that portion of the vagus craniad of the ganglion nodosum is
interconnected by a network of nervous fibres with the sympathetic
(_e_), hypoglossal (_b_), and accessory (_c_) nerves. From the ganglion
nodosum the vagus (_d′_) passes caudad, closely bound up with the
sympathetic; the two lie at the side of the common carotid artery. Just
before entering the thorax the two separate, the vagus being the larger
and lying ventrad of the sympathetic. (In rare cases the two are
distinctly separated throughout their length.)

  [Illustration: FIG. 156.--GLOSSOPHARYNGEAL, HYPOGLOSSAL, VAGUS,
  SYMPATHETIC, AND FIRST CERVICAL NERVES IN THE NECK.

  _a_, N. glossopharyngeus; _b_, N. hypoglossus; _c_, N. accessorius;
  _d_, ganglion nodosum of vagus nerve; _d′_, N. vagus; _e_, ganglion
  cervicale superius of sympathetic; _f_, ramus descendens of N.
  hypoglossus (united with first cervical); _g_, branch to M. thyrohyoid
  from ramus descendens of N. hypoglossus; _h_, N. laryngeus superior of
  N. vagus; _i_, united vagus and sympathetic nerves; _j_, first
  cervical nerve; _k_, second cervical nerve; _l_, N. pharyngeus from
  vagus. 1, M. masseter; 2, outline of external ear; 3, M. splenius; 4,
  M. levator scapulæ ventralis; 5, M. longus capitis; 6, trachea; 7, M.
  sternothyreoideus; 8, M. sternohyoideus; 9, M. thyreohyoideus; 10, M.
  constrictor pharyngis inferior; 11, M. constrictor pharyngis medius;
  12, cut end of M. stylohyoideus; 13, M. hyoglossus; 14, M.
  stylopharyngeus; 15, bulla tympani; 16, M. jugulohyoideus; 17, M.
  styloglossus; 18, M. mylohyoideus.]

Branches of the vagus in the cervical region (Fig. 156).

_a._ =N. auricularis.=--This leaves the ganglion jugulare, passes into
the petrous bone to the facial canal, leaves the skull with the facial
nerve by the stylomastoid foramen, and is distributed to the external
ear.

_b._ =N. pharyngeus= (_l_).--This leaves the vagus craniad of the
ganglion nodosum, passes ventrad, sends a small communicating branch
to N. laryngeus superior (_h_), and is distributed to the pharyngeal
muscles and cranial part of the œsophagus.

_c._ =N. laryngeus superior= (_h_).--This arises from the ganglion
nodosum, passes ventrad, crossing the medial surface of the carotid
artery, and reaches the larynx at about the level of the caudal end of
M. thyreohyoideus. It passes into the larynx and supplies its mucosa.

=Thoracic Portion of the Vagus= (Fig. 157).--As the vagus (_b_) and
sympathetic (_c_) separate to enter the thorax, the vagus (_b_) lies
more ventrad. The right vagus now lies along the lateral surface of the
trachea, the left one (Fig. 157) along that of the œsophagus. At about
the level of the first rib or further craniad there arise, apparently
from the vagus (but really from the sympathetic), two slender nerves
which pass caudad parallel and close to the vagus, lying slightly dorsad
of it. These are the =cardiac nerves= (_i_); they arise from the
sympathetic farther craniad in the neck region, accompany the vagus, and
seem to branch from it. In cases where vagus and sympathetic are
separate throughout their courses, these nerves arise clearly from the
sympathetic. The cardiac nerves pass to the heart and aid in forming a
network of nerves known as the =cardiac plexus= (_k_).

The vagus usually receives also, at about the level of the first rib,
one or two communicating branches from the middle cervical ganglion
(_d_) of the sympathetic. It then passes to the roots of the lungs,
crossing the lateral surface of the aortic arch on the left side, and
the medial surface of the azygos vein on the right side. As it crosses
the aortic arch the left vagus gives off =N. laryngeus inferior= (_j_).
This curves around the caudal side of the aortic arch to the lateral
surface of the trachea (_o_), then extends on the lateral and ventral
surface of the trachea craniad into the neck region. In the neck it
passes to the dorsolateral side of the trachea and reaches the larynx.
It passes into the larynx between the cricoid and thyroid cartilages,
and supplies the muscles of the larynx. It anastomoses with the superior
laryngeal.

  [Illustration: FIG. 157.--SYMPATHETIC, VAGUS, AND PHRENIC NERVES IN
  THE NECK AND THORAX.

  1-13, the thirteen ribs (cut); _V_-_VIII_, the fifth to eighth
  cervical nerves (cut); _I′_, first thoracic nerve (cut). _a_, combined
  trunk of vagus and sympathetic; _b_, vagus; _c_, sympathetic; _d_,
  middle cervical ganglion of sympathetic; _e_, inferior cervical
  ganglion; _e′_, communicating branch to sixth, seventh, and eighth
  cervical nerves; _f_, phrenic nerve; _g_, loop of sympathetic about
  subclavian artery, between the middle and inferior cervical ganglia;
  _h_, cardiac branches from the inferior cervical ganglion; _i_,
  cardiac branch passing from sympathetic along with vagus to heart;
  _j_, inferior laryngeal nerve; _k_, pulmonary and cardiac plexus; _l_,
  ventral œsophageal branch of vagus; _l′_, similar branch from the
  opposite side; _m_, dorsal œsophageal branch of vagus; _n_, great
  splanchnic nerve; _o_, trachea; _p_, œsophagus; _q_, aorta; _r_,
  heart; _s_, root of lung.]

The _right_ inferior laryngeal nerve is given off from the right vagus
much further craniad than the left; it curves around the right
subclavian artery just caudad of the origin of the internal mammary
artery, then passes to the trachea, and has a course and distribution
like that of the left side.

On reaching the root of the lungs the vagus divides into numerous
branches which form the =pulmonary plexus= (_k_) over the roots of the
lungs, and extends onto the basis of the heart as the =cardiac plexus=.
From these plexuses numerous branches pass to the heart, lungs,
pulmonary artery, pericardium, etc. The cardiac branches from the
sympathetic, mentioned above, are also connected with the cardiac
plexus.

Caudad of the pulmonary plexus the vagus is continued on each side as
two trunks, a =dorsal= (_m_) and a =ventral= (_l_) which pass along the
œsophagus (_p_). The ventral branches of right and left vagi (_l_ and
_l′_) unite a short distance caudad of the root of the lung, and the
single trunk extends into the abdominal cavity on the ventral surface of
the œsophagus. The dorsal branches of right and left vagi unite farther
back, near the diaphragm, and the single trunk thus formed (_m_) enters
the abdominal cavity on the dorsal surface of the œsophagus. Both
divisions give fine nerves to the œsophagus.

=Abdominal Portion of the Vagus= (Fig. 164, page 407).--After passing
through the diaphragm the ventral division (Fig. 164, _l_) reaches the
lesser curvature of the stomach (1), over which it ramifies, some
branches being traceable almost to the pylorus. The network of branches
thus formed is the =anterior gastric plexus=. Some twigs from the
ventral division pass transversely across the cranial end of the stomach
and join the plexus formed by the dorsal division.

The dorsal division (_m_) of the vagus reaches the greater curvature of
the stomach, where it ramifies, forming the =posterior gastric plexus=.
Branches from this anastomose with the anterior gastric plexus and with
the cœliac plexus of the sympathetic (_e_).


XI. N. ACCESSORIUS.--The accessory (or spinal accessory) nerve arises
(Fig. 138, _XI_) by numerous rootlets from the lateral surface of the
medulla and of the spinal cord as far caudad as the fifth to seventh
cervical nerve. These spinal rootlets join to form a nerve which enters
the cranium through the foramen magnum. After receiving the rootlets
from the medulla, it leaves the cranial cavity along with the vagus and
glossopharyngeal by the jugular foramen. Just outside the foramen (Fig.
156, _c_) it becomes involved in a plexus of fine branches which
interconnect it with the vagus, sympathetic, and hypoglossal. It then
turns laterad and caudad (Fig. 158, 1) and pierces the cleidomastoid
muscle (_d_), to which it gives small branches. It then divides: one
branch enters the sternomastoid muscle; the other passes caudad along
the dorsal border of the levator scapulæ ventralis, sends branches to
the clavotrapezius, and may be traced to the acromiotrapezius and
spinotrapezius, which it supplies.


XII. N. HYPOGLOSSUS (Fig. 156, _b_).--The twelfth or hypoglossal nerve
arises from the ventral side of the medulla (Fig. 138, _XII_), as
previously described. It emerges from the skull through the hypoglossal
canal. At first it passes ventrad, then gradually turns craniad,
following thus a curved course and passing successively laterad of the
vagus and sympathetic nerves (Fig. 156, _d_ and _e_), the common carotid
artery, and the cranial cornu of the hyoid bone. A short distance from
its origin the nerve gives off a =ramus descendens= (Fig. 156, _f_),
which receives a communicating branch from the first cervical nerve
(_j_), and divides into two branches, one (_g_) to the thyrohyoid muscle
(9), the other to the sternohyoid (8) and sternothyroid muscles (7). The
main nerve passes beneath the mylohyoid muscle into the tongue, at first
following the lingual artery, then laterad of it, then crossing it
again. It sends branches to all the muscles of the tongue, and may be
traced to its tip.

The hypoglossal nerve is involved in the plexus just outside of the
jugular foramen, with which the vagus, sympathetic, and accessory nerves
are also connected.


2. =Spinal Nerves.=--The origin and general features of the spinal
nerves have been described in connection with the account of the spinal
cord (page 337). A description of their peripheral distribution will now
be given.


A. CERVICAL NERVES.--There are eight pairs of cervical nerves. The first
leaves the vertebral canal through the atlantal foramen. The second
passes out between the arches of the atlas and axis, not through a
special intervertebral foramen, so that its ganglion lies among the
muscles of the back of the neck. The others emerge through the
intervertebral foramina, the eighth one from between the last cervical
and first thoracic vertebræ.

  [Illustration: FIG. 158.--SUPERFICIAL NERVES OF THE NECK.

  M. clavotrapezius has been partly removed. 1, N. accessorius; 2-4,
  ventral rami of second to fourth cervical nerves; 5, N. auricularis
  magnus; 6, N. cutaneus colli. _a_, M. clavotrapezius (cut); _b_, M.
  splenius; _c_, M. levator scapulæ ventralis; _d_, M. cleidomastoideus;
  _e_, M. sternomastoideus; _f_, parotid gland.]

=Dorsal Rami= (Rami posteriores).--The dorsal ramus of the first nerve
(N. suboccipitalis) supplies the short dorsal muscles which move the
head and connect the atlas and skull. In the second nerve the dorsal
ramus is much larger, forming =N. occipitalis major=. It sends small
branches to the muscles about its origin, then turns craniad on the
surface of the obliquus superior muscle, passes through the biventer
cervicis and splenius, joins a small branch from the third nerve, and
reaches the dorsal surface of the back of the head. It passes craniad,
lying beneath the levator auris longus, emerges from between the two
divisions of this muscle, and supplies the skin and cutaneous muscles
between the two external ears. The dorsal rami of the other cervical
nerves supply muscles and integument on the back of the neck.

=Ventral Rami= (=rami anteriores=).--These pass ventrad between the
transverse processes of the vertebræ, except in the case of the =first=
nerve (Fig. 156, _j_). This passes ventrad from the atlantal foramen
along the groove for the vertebral artery, through the notch in the wing
of the atlas, and across the lateral surface of the longus capitis
muscle (5). Here it sends a branch caudad to join the second cervical
(_k_), then crosses the vagus (_d′_) and sympathetic and the carotid
artery, giving off communicating branches to the vagus and sympathetic,
and uniting with a branch of the descending ramus of the hypoglossal
(_f_). At the lateral surface of the larynx it turns caudad, following
the lateral border of the sternothyroid muscle (7), and is distributed
to the sternohyoid (8) and sternothyroid (7).

The ventral ramus of the =second= nerve (Fig. 158, 2) receives a branch
from that of the first nerve, passes laterad between the levator scapulæ
ventralis (_c_) and the cleidomastoid (_d_), receives a communicating
branch from the third cervical (3), sends a branch to N. accessorius (1)
and numerous small nerves into the sternomastoid (_e_) and cleidomastoid
(_d_), then turns craniad and divides into =N. auricularis magnus= (5)
and =N. cutaneus colli= (6).

=N. auricularis magnus= (5), the great auricular nerve, passes
dorsocraniad across the lateral surface of the sternomastoid (_e_) to
the lateral and caudal surface of the external ear and parotid gland
(_f_), where it ramifies. The =cutaneus colli= (6) is the smaller,
ventral, division of the second nerve; it may receive also an accession
from the third. It passes to the integument over the ventral part of M.
masseter and ventrad of that muscle.

The =third= nerve (Fig. 158, 3) communicates with the second and
supplies the levator scapulæ ventralis (_c_), cleidomastoid (_d_),
sternomastoid (_e_), longus capitis, and other muscles of this region
and aids in forming the cutaneus colli (6). The =fourth= (4) and =fifth=
are distributed to the muscles and integument of the sides of the neck.
A branch of the fourth supplies the integument in the hollow of the
shoulder, and one from the fifth follows the vena cephalica and supplies
the integument over the shoulder. The fifth by sending a branch to aid
in forming the phrenic nerve (Fig. 157, _f_) may be considered to enter
partly into the brachial plexus.

Owing to the intercommunicating branches between the ventral roots of
the first five cervical nerves, these are sometimes considered as
forming a loose plexus which receives the name =cervical plexus=.

The sixth, seventh, and eighth cervical nerves (with a part of the
fifth) become interconnected with each other and with the first thoracic
to form the =brachial plexus=.


=The Brachial Plexus= (Fig. 159).--The brachial plexus is formed by the
ventral rami of the fifth, sixth, seventh, and eighth cervical nerves
and the first thoracic. Of the fifth cervical only a small part enters
into the plexus, forming part of the phrenic nerve. The formation of the
plexus is due to the union of the different nerves by means of strong
connecting branches or =ansæ=. The plexus lies in the axilla, along with
the axillary artery and vein; all its component nerves pass laterad in
front of the first rib. Its branches supply the arm and shoulder.

The precise arrangement of the different strands is somewhat variable.
The plexus is commonly made up in approximately the following manner
(Fig. 159). From the =fifth= cervical nerve (_V_) a small branch joins a
similar one from the sixth to form the phrenic nerve (_a_); the
remainder of the fifth does not enter into the plexus. From the =sixth=
cervical (_VI_) arise parts of the phrenic nerve (_a_), the
suprascapular (_b_), the cranial one of the three subscapular nerves
(_c_), the axillary (_d_), and the musculocutaneous (_f_). The sixth
also gives off close to its origin a nerve (_b′_) which passes to the
inner surface of the levator scapulæ and ramifies over the surface,
supplying this muscle and extending to the rhomboideus, which it also
innervates. The =seventh= cervical (_VII_) is the largest nerve entering
into the plexus; it furnishes parts of one or both of the anterior
thoracic nerves (_k_ and _n_), of the posterior thoracic (_m_), the
three subscapular nerves (_c_, _e_, and _i_), the axillary (_d_),
musculocutaneous (_f_), radial (_h_), and median (_g_) nerves. The
=eighth= cervical (_VIII_) supplies parts of one of the anterior
thoracic nerves (_k_), the caudal one of the subscapular nerves (_i_),
the radial (_h_), median (_g_), and ulnar (_j_) nerves. The =first
thoracic= (1) curves craniad, so as to leave the thorax on the cranial
side of the first rib; it supplies the median cutaneous nerve (_l_) and
parts of the radial (_h_), ulnar (_j_), and median (_g_) nerves;
sometimes also a part of one (_k_) of the anterior thoracic nerves.

  [Illustration: FIG. 159.--DIAGRAM OF THE RIGHT BRACHIAL PLEXUS.

  _V_, _VI_, _VII_, _VIII_, the fifth to eighth cervical nerves. 1, the
  first thoracic nerve. _a_, phrenic nerve; _b_, suprascapular; _b′_,
  nerve to serratus anterior and levator scapulæ muscles; _c_, first or
  cranial subscapular nerve; _d_, axillary nerve; _e_, second
  subscapular; _f_, musculocutaneous; _g_, median; _h_, radial; _i_,
  third subscapular; _j_, ulnar; _k_, second anterior thoracic; _l_,
  medial cutaneous; _m_, posterior thoracic; _n_, first anterior
  thoracic.]

The following are the nerves which arise from the brachial plexus:

A. =Nerves of the Shoulder and Breast= (Fig. 160).

1. =Nn. thoracici anteriores.=--There are two anterior thoracic nerves.
One (Fig. 160, _h_; Fig. 159, _n_) arises from the seventh cervical and
passes to the pectoral muscles (9) along with the anterior thoracic
artery. The other (Fig. 159, _k_; Fig. 160, _q_ and _r_) arises usually
by two roots, one from the eighth cervical, one from the first thoracic;
it passes along with the long thoracic artery to be distributed to the
pectoralis muscles (Fig. 160, 8) and sometimes also to the latissimus
dorsi (7).

2. =N. thoracicus posterior.=--The posterior thoracic (or long thoracic)
nerve (external respiratory) (Fig. 159, _m_) arises from the seventh
cervical nerve near its beginning. It passes within the scalenus muscle
and extends caudad on the outer surface of the serratus anterior muscle,
which it supplies.

3. =N. suprascapularis= (Figs. 159 and 160, _b_).--The suprascapular
nerve arises from the sixth (and sometimes the seventh) cervical. It
passes laterad and gives off a branch which passes over the
shoulder-joint and penetrates the clavodeltoid muscle to be distributed
to the integument on the ventral surface of the upper arm. It then
follows the transversa scapulæ artery into the supraspinatus fossa and
accompanies the artery to be distributed to the supraspinatus and
infraspinatus muscles.

4. =Nn. subscapulares.=--The subscapular nerves are three. The cranial
one (Figs. 159 and 160, _c_) arises from the sixth and seventh cervical
and supplies the subscapular muscle. The middle one (Fig. 159, _e_)
arises from the seventh; it supplies principally the teres major. The
caudal one (Fig. 159, _i_) arises from the seventh and eighth cervical
and supplies the latissimus dorsi. (The points of origin from the plexus
vary.)

5. =N. axillaris= (or =circumflexus=) (Fig. 159, _d_).--The axillary
nerve arises from the sixth and seventh cervical nerves. It passes
toward the shoulder-joint, then follows the posterior circumflex artery
ventrad of the long head of the triceps to be distributed to the
spinodeltoid and acromiodeltoid. A branch of it continues to the
clavobrachial, which it supplies.

B. =The Phrenic Nerve= (Fig. 157, _f_, page 381).

6. =N. phrenicus.=--The phrenic nerve (internal respiratory) is formed
by the junction of two slender branches, one from the fifth and one from
the sixth cervical nerves (Fig. 159, _a_). (It is said to receive
sometimes a branch from the fourth.) It passes caudad into the thorax on
the ventral surface of the subclavian artery and then extends to the
diaphragm lying at the side of the inferior and superior venæ cavæ. It
is the motor nerve of the diaphragm.

  [Illustration: FIG. 160.--BLOOD-VESSELS AND THE MORE VENTRAL NERVES OF
  THE AXILLA, VENTRAL VIEW.

  The pectoral and clavobrachial muscles have been cut and laid aside,
  their ends being shown; only a part of the nerves are exhibited. 1, M.
  clavobrachialis; 2, cut end of M. pectoralis major; 3, cut end of M.
  pectoralis minor; 4, M. biceps; 5, M. teres major; 6, M.
  epitrochlearis, partly cut and turned back; 7, M. latissimus dorsi,
  partly cut; 8, M. pectoralis minor; 9, M. pectoralis major; 10, short
  portion of caput mediale of M. triceps brachii. _a_, branches of the
  thyrocervical axis to clavobrachial and clavotrapezius muscles; _b_,
  suprascapular nerve; _c_, first subscapular nerve; _d_,
  musculocutaneous nerve; _e_, median nerve; _f_, V. axillaris; _g_, A.
  axillaris; _h_, first anterior thoracic nerve, accompanied by the
  anterior thoracic artery and vein; _i_, V. subscapularis; _j_, large
  muscular branch (to subscapular muscle) of the subscapular vein and
  brachial artery; _l_, A. subscapularis; _l′_, A. circumflexa humeri
  anterior; _m_, radial nerve; _n_, ulnar nerve; _o_, medial cutaneous
  nerve; _p_, A. thoracica longa; _q_, _r_, second anterior thoracic
  nerve; _s_, V. thoracica longa; _t_, A. and V. thoracicodorsalis; _u_,
  A. profunda brachii; _v_, branch of brachial artery accompanying
  medial cutaneous nerve; _w_, branch of A. collateralis radialis
  superior; _x_, A. collateralis radialis superior; _y_, V. mediana
  cubiti; _z_, A. collateralis ulnaris.]

C. =Nerves of the Arm.=

7. =N. musculocutaneus= (Fig. 160, _d_).--The musculocutaneous nerve or
external cutaneous arises from the ventral surface of the sixth and
seventh nerves (Fig. 159, _f_). It passes toward the shoulder-joint and
supplies the biceps (Fig. 160, 4) and coracobrachialis muscles. It then
passes distad, resting on the dorsal border of the biceps (4), and
supplies the brachialis muscle. Thence it passes dorsad of the biceps to
the lateral side, and reaches the integument by passing between the
clavobrachialis and pectoantibrachialis muscles near the elbow; it is
then distributed to the skin on the radial side of the ventral surface
of the forearm, as far as the wrist (Fig. 130, _h_, page 319).

8. =N. cutaneus medialis= (Fig. 160, _o_).--The medial (or internal)
cutaneous nerve rises from the first thoracic. It passes distad along
the medial side of the biceps, and at the junction of the second and
third thirds of the upper arm reaches the integument by passing between
the epitrochlearis and pectoantibrachialis muscles. It then curves
spirally about the dorsal border of the forearm and is distributed to
the integument of the forearm on the ulnar side, extending nearly to the
wrist.

9. =N. medianus= (Fig. 160, _e_).--The median nerve is formed by the
junction of three branches, one each from the seventh and eighth
cervical with the brachial artery (_g_) passing between them, and one
from the first thoracic nerve. It accompanies the brachial artery (_g_)
lying on its medial side, and passes with it through the supracondyloid
foramen; here it is connected by a branch to the musculocutaneous nerve.
It passes into the forearm (Fig. 161, _b_), lying at first beneath the
pronator teres (5). Here it gives branches to the pronator teres and
flexor muscles (flexor carpi radialis, palmaris longus, five heads of
the flexor profundus digitorum, but _not_ to the flexor carpi ulnaris).
Continuing along the forearm, lying on the flexor carpi radialis, it
sends a =posterior interosseous= nerve to the pronator quadratus muscle
and branches to the deep and superficial divisions of the flexor
sublimis digitorum. It thus supplies the =flexor= and =pronator= muscles
(except the flexor carpi ulnaris). It then passes into the palm beneath
the transverse ligament and gives rise to three principal branches. The
first of these supplies the integument of the thumb, sending a branch on
either side of it; and onto the radial side of the second digit. The
second passes along the contiguous sides of the second and third digits
and supplies their integument. The third passes along the contiguous
sides of the third and fourth digits to their integument. Each sends
twigs into the trilobed pad in the palm, so that there are thus seven
terminal branches in the palm. From these, branches (probably) pass to
the three radial Mm. lumbricales.

  [Illustration: FIG. 161.--NERVES AND ARTERIES OF THE FOREARM, SEEN
  FROM THE FLEXOR SIDE.

  Mm. palmaris longus, flexor carpi radialis, flexor carpi ulnaris, and
  the third and fourth heads of M. flexor profundus digitorum have been
  removed; also part of the pronator teres. 1, M. biceps; 2, conjoined
  tendon of M. brachialis and M. clavobrachialis; 3, short portion of
  caput mediale of M. triceps; 4, intermediate portion of caput mediale
  of M. triceps brachii; 5, cut ends of M. pronator teres; 6, M.
  brachioradialis; 7, M. extensor carpi radialis longus and brevis; 8,
  fifth head of M. flexor profundus digitorum; 9, second head of M.
  flexor profundus digitorum; 10, radial part of M. flexor sublimis
  digitorum; 11, common tendon of M. flexor profundus digitorum; 12,
  first head of M. flexor profundus digitorum; 13, cut origin of M.
  flexor carpi ulnaris. _a_, ulnar nerve; _b_, median nerve; _c_, dorsal
  cutaneous branch of the ulnar nerve; _d_, palmar branch of ulnar
  nerve; _e_, deep palmar branch; _f_, superficial palmar branch; _g′_,
  A. brachialis; _g_, A. radialis; _h_, A. collateralis ulnaris
  superior; _i_, A. radialis recurrens; _j_, A. ulnaris recurrens; _k_,
  A. ulnaris; _l_, A. interossea anterior; _m_, large branch of A.
  radialis, joining A. ulnaris.]

10. =N. radialis.=--The radial (or musculospiral) nerve is formed by the
junction of branches from the seventh and eighth cervical and first
thoracic nerves. It immediately sends branches to the epitrochlearis,
long head of the triceps, and long and intermediate portions of the
medial head of the triceps. It then passes between the long and
intermediate portions of the medial head of the triceps, following the
profunda brachii artery, and curves about the humerus to its cranial
side. It supplies there the lateral head of the triceps and the
anconeus, and, lying on the brachialis muscle, divides into a
superficial and a deep branch. The superficial branch is the
=superficial radial nerve= (Fig. 130, _g_); the deep one forms the
=dorsal= (or posterior) =interosseous nerve=. The former is sensory and
the latter motor.

The =superficial radial= nerve (Fig. 130, _g_, page 319) becomes
cutaneous at the junction of the second and third thirds of the upper
arm, where it emerges from between the lateral head of the triceps and
the brachialis muscle. It then follows the course of the vena cephalica
(_c_) to the wrist and follows the dorsal tributary of the same vein
onto the dorsum of the hand. It supplies the integument of the distal
part of the ventral surface of the upper arm and that along the forearm.
On the hand it is distributed to the dorsal surface in the same manner
as the median nerve on the ventral surface, i.e. to the integument of
the thumb on both sides and to that of the medial side of the second
digit; to that of the contiguous sides of the second and third digits
and of the contiguous sides of the third and fourth digits. There are
thus seven terminal branches, one for each of these regions.

The =dorsal interosseous= nerve follows the brachialis muscle and passes
onto the forearm between it and the extensor carpi radialis longus. It
supplies the =supinator= and =extensor= muscles of the forearm
(brachioradialis, supinator, extensor carpi radialis longus, extensor
carpi radialis brevis, extensor communis digitorum, extensor digitorum
lateralis, extensor indicis, extensor brevis pollicis). The dorsal
interosseous and radial nerves thus supply all the extensor muscles of
the forearm and upper arm and the supinators (modified extensors).

11. =N. ulnaris= (Fig. 160, _n_).--The ulnar nerve arises from the
eighth cervical and first thoracic and accompanies the brachial artery
(_g_) and median nerve (_e_) through the upper arm. It does not pass
through the supracondyloid foramen, but curves over the dorsal end of
the medial epicondyle of the humerus within the short division of the
medial head of the triceps, and reaches the dorsal border of the
forearm. In the forearm (Fig. 161, _a_) it lies beneath the flexor carpi
ulnaris. It supplies muscular branches to the flexor carpi ulnaris and
the first or ulnar head of the flexor profundus digitorum. Near the
middle of the forearm it divides into two branches, =dorsal cutaneous=
(_c_) and =palmar= (_d_).

The =dorsal cutaneous= branch (_c_) curves about the ulnar side of the
wrist to the dorsum of the hand and divides into twigs which supply the
dorsal part of the ulnar side of the fifth digit and of the contiguous
sides of the fourth and fifth. The =palmar branch= (_d_) sends a twig to
the integument on the flexor surface of the arm near the wrist, and then
divides into deep palmar (_e_) and superficial palmar (_f_) branches.

The =superficial palmar branch= (_f_) passes into the palm and supplies
the ventral portion of the integument on the ulnar side of the fifth
digit, and on the contiguous sides of the fifth and fourth.

The =deep palmar branch= (_e_) passes into the palm, beneath the
ligament of the pisiform bone. Just distad of the pisiform bone it
curves toward the radial side and breaks up into a number of small
branches which are distributed to the short muscles in the palm.


B. THORACIC NERVES.

=Dorsal Rami.=--The dorsal rami of the thoracic nerves are small and
supply the muscles and integument of the back. Each gives off a branch
directly dorsad to the spinal muscles, and a lateral branch which
reaches the integument some distance from the middle line.

=Ventral Rami.=--The ventral ramus of the first thoracic nerve enters
into the brachial plexus, as already described. The ventral rami of the
other thoracic nerves form the =intercostal nerves=. Each of these
passes ventrolaterad, lying close to the caudal border of a rib, in
company with the intercostal artery. Branches are given to the
intercostal muscles, and at about the middle of the length of the rib a
large lateral branch is given off, which passes to the more superficial
muscles of the thoracic wall (serrati posteriores, obliquus externus,
etc.), its main branches running dorsad and ventrad. The main
intercostal nerve extends ventrad to the transversus costarum and rectus
abdominis, supplying these muscles.


C. LUMBAR NERVES.--There are seven lumbar nerves, one passing from the
vertebral canal caudad of each lumbar vertebra.

=Dorsal Rami.=--The dorsal rami are similar to those of the thoracic
region, sending one branch dorsad to the muscles of the vertebral
column, another dorsolaterad to reach the integument at about the
lateral border of the longissimus dorsi. The dorsal rami are somewhat
smaller caudad.

=Ventral Rami.=--The last four lumbar nerves are interconnected to form
the =lumbar= or =lumbosacral plexus=. The first three are distinct, and
will therefore be described separately.

The first three lumbar nerves are directed strongly caudad (as well as
ventrad), so that on leaving the intervertebral foramen they pass
ventrad of the transverse process of the vertebra immediately
succeeding. Each communicates with the sympathetic system and gives off
near its origin branches to the muscles on the ventral side of the
vertebræ,--the first to the crus of the diaphragm, the second and third
(Fig. 162, _II_ and _III_) to the quadratus lumborum and psoas muscles.
Each divides three to five centimeters from its origin into a =lateral=
and a =medial= branch, the first having a more cranial, the latter a
more caudal course. The first three nerves of the cat are represented in
man by the iliohypogastric and the ilioinguinal nerves. There seems no
good ground for applying these names to two of the three in the cat, in
preference to the third, so that we shall speak of these nerves in the
cat as simply the first, second, and third lumbar nerves.

1. The first lumbar nerve arises from the intervertebral foramen caudad
of the first lumbar vertebra. Its lateral division passes between the
transversus and obliquus internus muscles, then between the obliquus
internus and externus. At about the middle of the abdomen it pierces the
obliquus externus and is distributed to the integument of the middle of
the ventral surface of the abdomen. The medial division passes between
the obliquus internus and transversus, crosses the lateral division of
the second (lying mediad of it), and extends to the rectus abdominis,
which it supplies.

2. The second lumbar nerve (Fig. 162, _a_) divides, like the others,
into two branches. The lateral branch pierces the muscles of the
abdominal wall at the lateral border of the longissimus dorsi and
passes, lying just beneath the integument, ventrocaudad nearly to the
pubis. It supplies the integument of the caudal half of the abdomen and
of the fold between the thigh and abdomen. The medial branch passes at
first almost directly caudad, lying on the medial surface of the
transversus abdominis; it curves gradually ventrad, lying in the
substance of the transversus, and reaches the rectus abdominis three or
four centimeters craniad of the pubis.

3. The third lumbar nerve (_b_) is not united with the fourth, as in
many animals, but remains distinct. It divides one or two centimeters
from its origin. The lateral branch passes caudad to the outer surface
of the abdominal muscles, and extends, lying just beneath the
integument, to that portion of the abdominal wall which is partly
covered by the thigh. The medial branch passes caudad on the lateral
surface of the iliopsoas muscle, follows the iliolumbar artery for a
short distance, and gives branches to the caudal part of the transversus
and rectus abdominis muscles.


=The Lumbar Plexus= (Fig. 162).--The fourth, fifth, sixth, and seventh
lumbar nerves are interconnected by short branches, forming thus the
=lumbar plexus=. They are also connected with the sacral plexus, so that
the two are often considered together as the =lumbosacral plexus= (Fig.
162). In some other animals the first three lumbar nerves form also a
part of the plexus; but they are not connected with it in the cat.

The fourth lumbar nerve forms the genitofemoral (_c_) and part of the
lateral cutaneous (_d_) nerves, and is connected by a short strand with
the fifth. The fifth aids in forming the lateral cutaneous (_d_) and
femoral (_f_) nerves, and is connected by a short branch with the sixth.
The sixth lumbar is large; it forms the major part of the femoral (_f_)
and a large part of the obturator nerve (_g_), and sends a large
connecting branch caudad to join the seventh and thus pass into the
sacral plexus. The seventh passes caudad to join the sacral plexus and
aid in forming the great sciatic nerve (_h_); by its connection with the
sixth it aids in forming also the obturator nerve (_g_).

4. =N. genitofemoralis= (or N. lumboinguinalis) (_c_, _c′_, _c″_).--This
is a direct continuation of the fourth lumbar nerve. Its medial branch
(_c″_) passes along the medial surface of the iliopsoas (8) and the
psoas minor (9) to the external iliac artery, accompanies this, lying on
the ventral surface, from its origin to the point where it gives off the
profunda femoris, then accompanies the latter artery and passes onto
that branch of it that spreads out under the integument of the ventral
pelvic region. It crosses the spermatic cord and ramifies in the skin of
the proximal part of the medial side of the thigh. The lateral branch of
the genitofemoralis (_c′_) pierces the psoas minor (9), appearing on its
ventral surface opposite the fifth lumbar vertebra. It passes caudad on
the ventral surface of this muscle, crosses the iliolumbar artery, then
turns caudolaterad, passes through the abdominal wall, and is
distributed to the craniomedial surface of the thigh and to the adjacent
abdominal wall.

This nerve is variable in origin and in distribution. Its lateral branch
is sometimes lacking.

5. =N. cutaneus femoris lateralis= (_d_).--The lateral cutaneous nerve
arises from the connecting strand between the fourth and fifth nerves,
most of its fibres coming from the fifth. It passes caudoventrad between
the iliopsoas and psoas minor and accompanies the iliolumbar artery
across the ventral surface of the iliopsoas. It pierces the abdominal
wall in company with the artery and passes onto the cranial border of
the thigh. Its terminal branches are distributed to the integument along
with the branches of the iliolumbar artery,--supplying the lateral
surface of the femur and extending as far as the knee.

6. =N. femoralis= (_f_).--The femoral is a large nerve which rises by
strong roots from the fifth and sixth lumbar nerves. It gives branches
to the iliopsoas (8) and passes through that muscle to its ventral
surface. It leaves the abdominal cavity lying on the ventral surface of
the iliopsoas, and at the point where it pierces the abdominal wall it
divides into three (or four) branches. One (or two) of these pass to the
sartorius muscle. Another passes between the rectus femoris and vastus
medialis muscles, and divides into numerous branches which supply these
muscles and the vastus intermedius.

The third branch of the femoral is =N. saphenus= or the =long saphenous=
nerve (Fig. 127, _g_, page 310). This passes distad along with the
femoral artery and vein, giving a few twigs to the integument. Where the
long saphenous artery (_f_) separates from the femoral artery the nerve
follows the former and passes with it along the medial side of the lower
leg. At the knee and in the lower leg it gives off a number of cutaneous
branches, and finally divides just distad of the middle of the lower leg
into two main branches. Both of these pass to the concavity of the
ankle-joint and divide into fine branches, which form a sort of plexus
on the ankle and dorsal surface of the foot; branches from this can be
traced almost to the toes.

7. =N. obturatorius= (Fig. 162, _g_).--The obturator nerve arises from
the connecting band between the sixth and seventh nerves. It lies at
first laterad, then dorsad, of the common iliac vein, and passes almost
directly caudad to the cranial border of M. obturator internus (15).
Here it turns sharply laterad about the pubis, and passes through the
obturator foramen. It gives twigs to the obturator externus muscle, and
divides into several branches, which innervate the adductor femoris,
adductor longus, pectineus, and gracilis.

  [Illustration: FIG. 162.--THE LUMBAR AND SACRAL NERVES, AS SEEN IN A
  VIEW OF THE DORSAL WALL OF THE ABDOMINAL CAVITY, AFTER REMOVAL OF THE
  VISCERA.

  On the right side the iliopsoas, psoas minor, and quadratus lumborum
  have been removed. The symphysis pubis has been split and the two
  parts divaricated, to show the pelvic cavity; on the right side parts
  of the innominate bones and the levator ani and coccygeus muscles have
  been removed. _II-VII_, second to seventh lumbar nerves; 1-3, first to
  third sacral nerves. _a_, second lumbar nerve; _b_, lateral and medial
  branches of third lumbar nerve; _c_, N. genitofemoralis (_c′_, its
  lateral branch; _c″_, its medial branch); _d_, N. cutaneus femoralis
  lateralis; _e_, muscular branch of N. femoralis; _f_, N. femoralis;
  _g_, N. obturatorius; _h_, N. ischiadicus or great sciatic nerve; _i_,
  N. gluteus superior; _j_, N. gluteus inferior; _k_, N. cutaneus
  femoris posterior; _l_, N. pudendus; _m_, N. hemorrhoidalis inferior;
  _n_, part of the sympathetic (incompletely shown, merely to indicate
  connections with the spinal nerves); 4, M. transversus abdominis; 5,
  6, cut edges of M. obliquus internus and externus; 7, dorsal border of
  the diaphragm; 8, M. iliopsoas (mostly removed on the right side); 9,
  M. psoas minor; 10, M. pyriformis; 11, M. levator ani; 11′, M.
  iliocaudalis; 12, M. flexor caudæ longus; 13, M. flexor caudæ brevis;
  14, edge of pubic symphysis; 15, cut end of M. obturator internus; 16,
  cut ramus of ischium; 17, cut ramus of pubis.]


D. SACRAL NERVES AND SACRAL PLEXUS (Fig. 162).--A large band passes
caudad from the sixth and seventh lumbar nerves to connect with the
sacral nerves; this constitutes the so-called =lumbosacral cord=. The
sacral nerves are three in number. Their dorsal rami pass dorsad out of
the two posterior sacral foramina and the foramen caudad of the sacrum,
to the muscles and skin dorsad of the sacrum. The ventral rami pass from
the two anterior sacral foramina and from the foramen between the last
sacral and first caudal vertebræ. The first is the largest; it joins
the lumbosacral cord to form the great sciatic nerve (N. ischiadicus)
(_h_) and the superior (_i_) and inferior (_j_) gluteal, and sends a
branch caudad to connect with the second sacral. The second and third
sacral nerves are small; they unite with the connecting branch from the
first to form a network from which arises the pudendus (_l_), cutaneus
femoris posterior (_k_), hemorrhoidalis inferior (_m_), and a small
branch to the great sciatic (_h_).

The nerves arising from the sacral plexus are the following:

1. =N. gluteus superior= (Fig. 162, _i_; Fig. 163, _j_).--The superior
gluteal nerve arises from the lumbosacral cord and the first sacral
nerve; it passes dorsad in the notch between sacrum and ilium,
caudolaterad of the first anterior sacral foramen, curves over the
dorsal border of the ilium between the gluteus medius and pyriformis
muscles (Fig. 163, 7), passes between the gemellus superior (6) and
gluteus minimus (5) and ventrad of the latter, and reaches the medial
surface of the tensor fasciæ latæ, which it innervates. In its course it
sends branches to the gluteus medius, gluteus minimus (5), and gemellus
superior.

2. =N. gluteus inferior= (Fig. 162, _j_; Fig. 163, _i_).--A small nerve
from the lumbosacral cord and the first sacral nerve. It passes
dorsocaudad, lying on the dorsal surface of the great sciatic nerve
(Fig. 162, _h_). After leaving the pelvis by the great sciatic notch it
divides beneath the pyriformis (Fig. 163, 7) into two branches; one goes
to M. caudofemoralis (4), the other to M. gluteus maximus (3).

3. =N. ischiadicus= (Fig. 162, _h_; Fig. 163, _a_).--The =great sciatic=
nerve, the largest nerve in the body, arises from the lumbosacral cord
(formed chiefly by the sixth and seventh lumbar nerves), the first
sacral nerve and a small branch from the second sacral. It passes
caudodorsad and leaves the pelvis by passing across the great sciatic
notch, between M. pyriformis and M. gemellus superior. It passes across
the tendon of M. obturator internus (Fig. 163, 9) near the insertion,
and here sends caudad a large muscular branch (_b_) beneath the biceps.
This branch innervates the biceps, semitendinosus (17) and
semimembranosus (16). Other twigs in this region pass to the quadratus
femoris (10) and tenuissimus. The great sciatic nerve (_a_) now passes
across the quadratus femoris (10), adductor femoris (15), and
semimembranosus (16), lying beneath the biceps femoris. It thus enters
the popliteal space and approaches the popliteal artery and vein. Here
it gives off one or two small muscular branches to the distal part of
the biceps, and sends a slender branch, =N. suralis= (_c_), along the
medial surface of the biceps to the lateral surface of the lateral head
of M. gastrocnemius (20). The sural nerve (_c_) becomes cutaneous at the
distal (ventral) border of the biceps, and divides three or four
centimeters proximad of the ankle into two branches. One passes over the
tendon of Achilles (27) to the proximal end of the calcaneus and
ramifies in this region. The other passes onto the lateral surface of
the foot, and supplies the integument in this region over the tarsus and
part of the metatarsus.

The great sciatic nerve now divides in the popliteal space into the
=peroneus communis= (_d_) and the =tibialis= (_e_).

  [Illustration: FIG. 163.--DISSECTION OF LEG, LATERAL VIEW, TO SHOW
  DISTRIBUTION OF THE GREAT SCIATIC NERVE.

  The biceps, caudofemoralis, gluteus maximus, gluteus medius, tensor
  vaginæ femoris, and part of the peroneus longus have been removed.
  _a_, N. ischiadicus or great sciatic nerve; _b_, muscular branch; _c_,
  N. suralis; _d_, N. peroneus communis; _e_, N. tibialis; _f_, N.
  peroneus profundus; _g_, N. peroneus superficialis and its terminal
  branches; _h_, branches of N. cutaneus femoris posterior; _i_, N.
  gluteus inferior; _j_, N. gluteus superior; _k_, vena saphena parva;
  _k′_, communicating branch to V. glutea inferior. 1, M. sartorius; 2,
  cut origin of M. gluteus medius; 3, cut origin of M. gluteus maximus;
  4, cut origin of M. caudofemoralis; 5, M. gluteus minimus; 6, M.
  gemellus superior; 7, M. pyriformis; 8, M. flexor caudæ longus; 9, M.
  obturator internus; 10, M. quadratus femoris; 11, tuberosity of the
  ischium; 12, great trochanter of femur; 13, M. rectus femoris; 14, M.
  vastus lateralis; 15, M. adductor femoris; 16, M. semimembranosus; 17,
  M. semitendinosus (the slender ribbon-like muscle crossing this is M.
  tenuissimus); 18, M. vastus intermedius; 19, M. plantaris; 20, M.
  gastrocnemius; 21, M. peroneus longus (cut); 22, M. tibialis anterior;
  23, M. extensor longus digitorum; 24, transverse ligament; 25, M.
  peroneus brevis; 26, M. soleus; 27, tendon of Achilles; 28, M.
  extensor brevis digitorum; 29, tendon of M. peroneus tertius.]

_a._ =N. peroneus communis= (_d_).--This is the more lateral of the two
divisions of the great sciatic nerve. It passes along the medial surface
of the biceps to the lateral surface of the lateral head of M.
gastrocnemius (20), where it extends to a point just distad of the head
of the fibula. Here it passes beneath that part of the gastrocnemius
which has origin on the fascia of the shank, passes between the soleus
and peroneus longus (21), then between the peroneus longus and peroneus
tertius. It gives off a number of small muscular branches, then divides
two or three centimeters distad of the head of the fibula into two main
branches, =N. peroneus superficialis= (_g_) and =N. peroneus profundus=
(_f_).

(1) =N. peroneus superficialis= (_g_).--The superficial peroneal nerve
passes distad between the peroneus longus and peroneus tertius. Near the
ankle it becomes superficial, passing along the concavity of the ankle
across the transverse ligament which binds down the tendons of the
extensor longus (23) and tibialis anterior (22), and thus reaches the
dorsal side of the foot. Two or three minute twigs are given off to the
ankle, then the nerve divides into four divisions. These pass distad to
the toes, subdividing so as to send a nerve to each side of each toe.

(2) =N. peroneus profundus= (_f_).--The deep peroneal nerve passes
between the tibialis anterior and extensor longus digitorum muscles,
gives branches to these muscles, and passes distad with the tibialis
anterior artery, lying on the inner surface of the tibialis anterior
muscle. It passes onto the dorsum of the foot, lying on the inner
surface of the tendon of the muscle. On the tarsus it divides into two
branches. The lateral branch passes into the extensor brevis digitorum,
while the medial one extends in the dorsal groove between metatarsals
four and five to the toes; here it divides into two nerves which supply
the contiguous sides of digits four and five.

_b._ =N. tibialis= (_e_).--The tibial nerve passes distad parallel with
the peroneal nerve, but mediad of it. It passes between the lateral and
medial heads of the gastrocnemius, giving off muscular branches to
these, and to the plantaris and soleus. It then passes between the
plantaris and the medial head of the gastrocnemius, and reaches the
space between the plantaris and flexor longus hallucis, where it passes
distad. It gives off, in the region just described, muscular branches to
the flexor longus digitorum, flexor longus hallucis, and tibialis
posterior. Below the middle of the lower leg the nerve becomes
superficial (Fig. 127, _i_, page 310), lying on the ventral surface of
the flexor longus hallucis. It passes in the depression between the heel
and the medial malleolus onto the plantar surface of the tarsus, sends a
small branch to the plantar surface of the heel, and divides into two
branches, the =medial= and the =lateral plantar= nerves.

(1) =N. plantaris medialis.=--The medial plantar nerve passes along the
medial border of the flexor brevis digitorum and divides into two
branches. One passes to the medial (second) digit, supplying both sides;
the other supplies the third digit in the same way. Both send branches
to the fibrous pad on the sole of the foot.

(2) =N. plantaris lateralis.=--The lateral plantar nerve passes laterad
across the tendon of the flexor longus digitorum to its lateral edge. At
about the proximal end of the metatarsi it divides into two branches.
The lateral branch passes distad to the ventral surface of the fifth
digit. The medial branch passes beneath the tendon of the flexor longus
digitorum and transversely across the interossei; it divides into
numerous tendons which innervate the interossei and other short muscles
of the sole of the foot.

4. =N. pudendus= (Fig. 162, _l_; Fig. 112, 8, page 265).--This arises
(Fig. 162, _l_) from the sacral plexus caudad of the great sciatic
nerve. It has two roots, one from the second sacral, one from the third,
and it may also receive a small accession from the great sciatic nerve
(_h_) three or four centimeters caudad of the origin of the latter. It
passes at first dorsolaterad, laterad of the coccygeus muscle, then
curves mediad toward the anus. It divides into two branches: one passes
to the base of the penis, sends twigs into the compressor urethræ
muscle, and passes onto the dorsal surface of the penis. This branch is
=N. dorsalis penis=; it extends with the artery of the same name to the
glans. The second branch of N. pudendus (=N. hemorrhoidalis medius=)
passes to the anus and innervates the muscles and other structures about
the caudal end of the rectum. In the female, branches of N. pudendus
supply the urogenital sinus and adjacent structures (Fig. 112, 8).

5. =N. cutaneus femoris posterior= (Fig. 162, _k_; Fig. 163, _h_).--This
arises from the sacral plexus, its roots coming chiefly from the second
and third sacral nerves, and passes caudodorsad, at first in close
connection with N. pudendus. It then accompanies the posterior gluteal
artery and vein, sends branches (perineal nerves) into the fat at the
sides of the anus, and branches onto the lateral surface of the biceps
muscle. One of the latter follows the communicating vein (Fig. 163,
_k′_) from V. saphena parva, and may be traced as far distad as the
popliteal space.

6. =N. hemorrhoidalis inferior= (or =posterior=) (Fig. 162, _m_).--This
arises by two roots, from the second and third sacral nerves, and passes
with the inferior hemorrhoidal artery ventrad across the lateral surface
of the rectum to the urethra. Here it divides into two parts: one passes
craniad to the bladder, the other caudad onto the ventrolateral surface
of the rectum.

A small nerve passes from the sacral plexus, especially from the third
sacral nerve, into M. levator ani (Fig. 162, 11). Another small nerve
from the same region passes to M. coccygeus, and a third to the proximal
end of M. tenuissimus.


E. NERVES OF THE TAIL. COCCYGEAL NERVES.--From the intervertebral
foramina of the first seven or eight caudal vertebræ spinal nerves of
the usual type are given off. The dorsal rami innervate the dorsal
muscles of the tail. The ventral rami are interconnected with each other
and with the last sacral nerve by a longitudinal cord; they innervate
the muscles and integument of the ventral side of the tail.


3. The Sympathetic Nervous System. Systema nervorum sympathicum.

The sympathetic system consists essentially of a chain of ganglia on
each side of the ventral surface of the vertebral column, interconnected
by longitudinal nerve-cords, and stretching from the base of the skull
to the tail. The ganglia are connected to the spinal nerves by
communicating branches, and numerous branches pass from them to the
abdominal and thoracic viscera, and to the walls of the lymph- and
blood-vessels, forming complicated plexuses.

=Cervical portion= (Fig. 156, page 379).--The sympathetic system begins
just caudad of the tympanic bulla as the =superior cervical ganglion=
(=G. cervicale superius=) (Fig. 156, _e_). This is a large ganglion
closely applied to the ganglion nodosum (_d_) of the vagus, and lying on
its ventrocranial side. From the superior cervical ganglion the
sympathetic trunk passes caudad usually closely bound up with the vagus
(_d′_), so that the two can scarcely be distinguished. They lie (_i_) at
the side of the trachea (6), close against the lateral surface of the
carotid artery. A few centimeters before reaching the first rib the two
separate (Fig. 157, page 381); the sympathetic (_c_) is here the smaller
and more dorsal of the two. Just craniad of the first rib the
sympathetic usually forms a small swelling, the =middle cervical
ganglion= (Fig. 157, _d_), beyond which it divides into two portions.
The larger dorsal division passes dorsocaudad and joins a large
ganglion, the =inferior cervical= (_e_), which lies at the head of the
first rib, on the lateral surface of the longus colli muscle. The
ventral branch (_g′_) passes caudad, turns laterad about the medial and
caudal surface of the subclavian artery, and likewise reaches the
inferior cervical ganglion.

In some cases the middle cervical ganglion (_d_) is lacking.

=Branches of the Sympathetic in the Cervical Region.=--From the cranial
end of the superior cervical ganglion several nerves pass craniad. Some
of these become connected immediately with the cranial nerves emerging
from the jugular foramen, forming a plexus in this region. Others pass
with the internal carotid artery craniad, forming a plexus about that
artery; from the plexus twigs arise which pass to the fifth and sixth
cranial nerves; doubtless also to the seventh and eighth. A specially
large branch, the =deep petrosal nerve= (see page 373), passes from the
superior cervical ganglion along with the internal carotid artery to the
pterygoid canal, thence through this to the =sphenopalatine= ganglion.
Before separating from the vagus the sympathetic gives off one or two
=cardiac= nerves (Fig. 157, _i_). These are closely bound up with the
vagus (_b_), so that they appear usually to have origin from the vagus
at about the level of the first rib. These pass with the vagus to the
heart and take part in the formation of the =cardiac plexus= (_k_).

At the middle cervical ganglion (_d_) usually a communicating branch is
given to the vagus. The branches of the inferior cervical ganglion (_e_)
fall in the thoracic region, and are described in that connection.

=Thoracic Portion of the Sympathetic= (Fig. 157, page 381).--The
inferior cervical ganglion (_e_) lies entirely within the thoracic
cavity. It has the following branches:

1. One or two small =cardiac= branches (_h_), which pass to the heart
(_r_).

2. A =large communicating branch= (_e′_), which passes craniad from the
cranial end of the ganglion (_e_) along the lateral surface of the
longus colli muscle, and gives communicating branches to the sixth,
seventh, and eighth cervical nerves (_VI_, _VII_, and _VIII_).

3. One or two small communicating branches to the first thoracic nerve
(_I′_).

4. A communicating branch to the second thoracic nerve.

The arrangement of these communicating branches is somewhat variable;
they may arise in various combinations, as at first united, or as more
or less completely separated nerves.

The sympathetic trunk (_c_) continues caudad from the caudal end of the
inferior cervical ganglion, lying at first on the lateral surface of the
longus colli, then on the lateral surface of the centra of the vertebræ.
For each vertebra there is a slight enlargement, forming one of the
=thoracic ganglia= of the sympathetic, and from each ganglion one or
two =communicating branches= are given off to the corresponding spinal
nerve. Just caudad of the last rib (but while still in the thoracic
cavity) the sympathetic gives off the large =N. splanchnicus major= or
great splanchnic nerve (_n_), which passes ventrocaudad and pierces the
diaphragm. The sympathetic itself then passes through the diaphragm
laterad of the crus.

=Abdominal Portion of the Sympathetic= (Fig. 164).--The great splanchnic
nerve (_b_) passes through the diaphragm (2) laterad of the crus,
extends two or three centimeters caudoventrad, and joins a large
ganglion lying just caudad of the cœliac artery (4), almost on the
lateral surface of the superior mesenteric (5). This is the =cœliac= (or
semilunar) =ganglion= (_d_). From it nerves branch in all directions,
forming the =cœliac plexus= (_c_), a part of the large =solar plexus=.
Less than a centimeter ventrocaudad of the cœliac ganglion, on the
caudal surface of the superior mesenteric artery (5), is the somewhat
smaller =superior mesenteric ganglion= (_f_); the two are connected by
two strong nerve-trunks.

  [Illustration: FIG. 164.--SYMPATHETIC AND VAGUS IN THE ABDOMEN
  (SOMEWHAT SCHEMATIC).

  1, stomach; 2, crus and cut edge of diaphragm; 3, aorta; 4, cœliac
  artery; 5, superior mesenteric artery; 6, kidney; 7, inferior
  mesenteric artery; 8, large intestine. _a_, main trunk of sympathetic;
  _b_, great splanchnic nerve; _c_, lesser splanchnic nerves; _d_,
  cœliac (or semilunar) ganglion; _e_, cœliac plexus; _f_, superior
  mesenteric ganglion; _g_, superior mesenteric plexus, following the
  artery; _h_, aortic plexus; _i_, inferior mesenteric ganglion and
  plexus; _j_, suprarenal plexus on suprarenal body; _k_, renal plexus
  following renal artery; _l_, ventral œsophageal branch of vagus,
  forming anterior gastric plexus; _m_, dorsal œsophageal branch of
  vagus, forming posterior gastric plexus.]

The cœliac ganglion (_d_) receives from the sympathetic (_a_), in
addition to the great splanchnic nerve, two (or three) =lesser
splanchnic= nerves (_c_), which arise from the main trunk of the
sympathetic, the first just as it reaches the abdominal cavity, the
second one or two centimeters caudad of the diaphragm.

From the cœliac and superior mesenteric ganglia a network of nerves
passes in all directions to the abdominal viscera. These nerves follow
especially the arteries, forming plexuses over their surfaces, and
passing with them to the organs which they supply. The cœliac plexus
anastomoses with the =posterior gastric= plexus of the vagus. Parts of
the cœliac plexus following the branches of the cœliac artery may be
distinguished as =hepatic= plexus, =splenic= plexus, etc. A dense plexus
is formed on the surface of the suprarenal body (=suprarenal= plexus,
_j_), and a =renal= plexus (_k_) follows the renal artery to the kidneys
(6). The =superior mesenteric plexus= (_g_) forms a dense network over
the superior mesenteric artery (5) and follows it to the intestine. A
plexus passes caudad on the aorta (=aortic plexus=, _h_). This is a
continuation of the cœliac and superior mesenteric plexuses; it receives
a number of branches from the main sympathetic trunk, lying dorsad of
the aorta. The aortic plexus contains a number of small ganglia.

From the aortic plexus the smaller =inferior mesenteric= plexus (_i_)
follows the inferior mesenteric artery (7) to the large intestine; in
this lies a ganglion of considerable size, the =inferior mesenteric
ganglion=.

In the pelvic region small plexuses are formed in a similar manner, from
branches given off by the main sympathetic trunk, together with branches
from the plexuses of the abdominal cavity. These plexuses supply the
various organs in the pelvis.

The main sympathetic trunk (_a_) passes into the abdomen at the side of
the crus of the diaphragm, lying dorsad of the great splanchnic nerve
(_b_). In the abdomen it lies nearer the middle line than in the thorax,
so that the two trunks of right and left side are separated by but a few
millimeters as they lie on the ventral surface of the centra of the
lumbar vertebræ. There is a ganglion for each vertebra (Fig. 162, _n_),
and from each ganglion are given off one or more communicating branches
to the spinal nerves, and usually a branch which passes ventrad to join
one of the plexuses among the viscera. The first three branches of this
kind (Fig. 164, _c_) are larger and pass to the cœliac and superior
mesenteric ganglia. The sympathetic may be traced into the pelvis, where
it becomes smaller, and is lost as the caudal region is reached.



SENSE-ORGANS AND INTEGUMENT.


I. THE ORGAN OF SIGHT. ORGANON VISUS.

1. =The Orbit.=--The bony framework of the orbital fossa, in which the
organ of sight is situated, has already been described (page 53). The
orbit is not protected by bone on all sides, being open caudad and
ventrad, and partly laterad. The structures within the orbit are further
protected and separated from other structures by a very thin, tough,
transparent membranous sac, the =periorbita=, which surrounds them
almost completely and nearly fills the orbit. The periorbita forms a
conical sac with the apex of the cone directed caudoventrad and attached
about the optic foramen and orbital fissure. The base of the cone is
attached about the margin of the orbital fossa,--to the supraorbital
margin of the frontal, to the maxillary and malar bones, and to the
orbital ligament, connecting the frontal process of the malar with the
zygomatic process of the frontal. The periorbita is partly separated
from the walls of the orbital fossa by masses of fat. It comes in
contact, aside from the bones, with the temporal and pterygoid muscles,
and with nerves and blood-vessels in the orbit.

The sac thus formed encloses the eyeball with its muscles and glands
(Fig. 166), as well as a mass of fat in which these are imbedded. The
periorbita and its contents are freely movable with relation to
surrounding structures.

2. =The Eyelids. Palpebræ.=--The eyelids are two thin folds which
protect the eye. Externally they are covered with hair; internally by
the thin membranous =conjunctiva=. The eyelids contain the =Meibomian=
or =tarsal= glands, arranged in short rows passing perpendicularly
inward from the edge of the lids; these may sometimes be seen with the
naked eye as broad yellowish lines. They secrete a substance which
prevents the adhesion of the edges of the two lids. On the edge of each
eyelid, three to four millimeters from the medial angle of the eye, is
one of the openings of the lachrymal canals.

At the medial angle of the eye is the large =nictitating membrane=
(=membrana nictitans=), or “third eyelid,” corresponding to the plica
semilunaris of man. In the cat this is large and may cover the whole
surface of the eye. It is supported (Fig. 165) by a broad central strip
of cartilage (_a_), passing from its edge to its inner angle, and the
inner end of this cartilage is surrounded, on the medial (concave) side
of the membrane, by the large lobulated =Harderian= glands (_b_).

  [Illustration: FIG. 165.--INNER SURFACE OF MEMBRANA NICTITANS,

  showing the supporting cartilage and Harderian glands. _a_, supporting
  cartilage; _b_, Harderian glands; _c_, outer edge.]

The =conjunctiva= is the thin membrane covering the inner surface of the
lids, the outer surface of the eyeball, and both surfaces of the
nictitating membrane.

The muscles of the eyelids are =M. orbicularis oculi=, already described
(page 98), and =M. levator palpebræ superioris=, described below.

3. =Lachrymal Apparatus.=--The =lachrymal gland= is a large reddish
gland, not lobulated externally, which lies on the surface of the
eyeball just beneath the lateral angle of the eye. The gland is situated
immediately craniad of, and in contact with, the zygomatic process of
the frontal bone (Fig. 154, 11, page 374). It is flat and about one
centimeter in diameter. The ducts which pass from the gland to the eye
are not visible to the naked eye. The fluid secreted by the gland
collects at the medial angle of the eye and passes into the two openings
of the lachrymal canals, one of which is found on the pigmented edge of
each lid, three or four millimeters from the medial angle of the eye.
The canals passing from these openings soon unite to form the
=nasolachrymal duct=, which passes through the lachrymal bone, along the
medial surface of the maxillary, to open into the nasal cavity ventrad
of the ventral concha of the nose.

4. =Muscles of the Orbit= (Fig. 166).--Within the orbit are eleven
muscles, ten connected with the eyeball, and one, M. levator palpebræ
superioris, with the upper eyelid.

Of the ten muscles of the eyeball, eight are straight muscles, passing
from an origin about the inner end of the orbit directly distad; the
other two have an oblique direction. Four of the straight muscles are
larger and are known as the =Mm. recti= (_b_, _c_, _d_); these are
distinguished according to their position as =lateral= (_c_), =medial=,
=superior= (_d_), and =inferior= (_b_). The four smaller straight
muscles constitute together =M. retractor oculi= (_e_). The two oblique
muscles are known as =Mm. obliqui= and are distinguished according to
their position as =inferior= (_a_) and =superior=.

  [Illustration: FIG. 166.--MUSCLES OF THE EYEBALL, LATERAL VIEW.

  _a_, M. obliquus inferior; _b_, M. rectus inferior; _c_, M. rectus
  lateralis; _d_, M. rectus superior; _e_, parts of M. retractor oculi;
  _f_, the oculomotor nerve.]

=Mm. recti= (_b_, _c_, _d_).--The four recti muscles arise from the bone
about the optic foramen and pass toward the eyeball. They are inserted
by thin, flat tendons along a line which separates the darker caudal
part of the sclerotic from the white zone of the sclerotic which borders
the cornea,--the line of insertion of the four tendons forming thus a
circle about the eyeball. The rectus superior (_d_) is partly covered by
M. levator palpebræ superioris. The tendon of the rectus inferior (_b_)
is crossed by M. obliquus inferior (_a_). The recti muscles are all
innervated by the oculomotor (third) nerve (_f_), except the lateral
(_c_), which is supplied by the abducens (sixth) nerve.

=M. retractor oculi= (_e_).--The retractor oculi arises about the optic
foramen and divides into four heads which lie nearer the eyeball than
the recti and are therefore partly covered by the latter. They alternate
with the recti and are inserted into the eyeball at about its equator,
except the inferior division, which is inserted on a line with the
recti. They are supplied by the oculomotor nerve.

=M. obliquus inferior= (_a_).--The inferior oblique arises from the
maxillary bone just laterad of the lachrymal bone and curves over the
ventral side of the eyeball along the lines of insertion of the recti,
crossing the tendon of the rectus inferior (_b_) to the ventral edge of
the tendon of the lateral rectus (_c_), where it is inserted. It rotates
the eyeball and is supplied by the third nerve (_f_).

=M. obliquus superior.=--The superior oblique takes origin from the
cranial border of the optic foramen, passes dorsocraniad, and ends in a
small rounded tendon which passes through a fibrous pulley-ring. This
ring is situated near the rim of the orbit, one or two centimeters
craniad of the zygomatic process of the frontal bone, and is attached to
the wall of the orbit by two fibrous bands. After passing through the
pulley-ring the tendon turns and passes laterocaudad; it becomes much
expanded, passes caudad of the superior rectus, and is inserted into the
eyeball along the caudal margin of the insertion of the superior rectus
tendon. The superior oblique is supplied by the trochlear (fourth)
nerve.

=M. levator palpebræ superioris.=--This is a small thin muscle which
takes origin on the wall of the optic foramen close to the rectus
superior, passes over the outer surface of the rectus superior and
beneath the lachrymal gland, and forms a thin tendon which is inserted
into the margin of the upper eyelid. It is innervated by the oculomotor.

5. =The Eyeball.=--The eyeball is approximately spherical in form, but
the cranial surface has a slightly greater curvature than the caudal
portion, so that the eye appears slightly pointed at the cranial (free)
surface. The large cylindrical =optic nerve= (Fig. 167, _a_) enters the
eyeball at nearly the centre of the caudal half of the eye. On the outer
surface is seen the transparent =cornea= (_c_), covering the free
surface of the eye, and the opaque =sclerotic= (_b_), covering the
remainder of the ball. Through the cornea can be seen the yellow
curtain-like =iris=, with an opening in its centre, the =pupil=.

  [Illustration: FIG. 167.--DIAGRAM OF A SECTION OF THE EYE.

  _a_, optic nerve; _b_, sclerotic (_b′_, thickened “white zone”); _c_,
  cornea; _d_, choroid; _e_, iris; _f_, ciliary body; _g_, retina; _h_,
  crystalline lens; _i_, zonula ciliaris; _j_, anterior chamber of eye;
  _k_, vitreous humor.]

=Coats of the Eye= (Fig. 167).--The outer coat of the eyeball is formed
by the =sclerotic= (or sclera) (_b_) and the =cornea= (_c_). The
sclerotic is the whitish opaque portion covering the caudal
three-fourths of the eye. It forms a tough sac serving as a protection
for the structures within. The cornea (_c_) is the circular transparent
portion of the outer coat, covering the free surface of the eye; it is a
direct continuation of the sclerotic. Just before passing into the
cornea the sclerotic is much thickened, forming a broad white zone
(_b′_) about the eyeball near its equator. To this zone, at its caudal
margin, are attached the rectus muscles of the eyeball. The sclerotic
has many pigment-cells on its inner surface, giving it a brownish
appearance and forming the =lamina fusca=.

The =cornea= (_c_) is transparent and more strongly curved than the
sclerotic. It is thicker than most of the sclerotic coat, but not so
thick as the white zone of the latter.

Within the sclerotic is the second coat of the eye, formed by the
=choroid= (_d_) and the =iris= (_e_). The choroid (_d_) is a vascular
layer, and contains much pigment, giving it a dark color. It lines the
inner surface of the sclerotic, but does not cover the inner surface of
the cornea. At the white zone of the sclerotic it is thrown into a large
number (about seventy) of meridional folds, the plicæ ciliares or
ciliary folds, which together constitute the so-called =ciliary body=
(=corpus ciliare=) (_f_). This forms a circular zone on the inner
surface of the white zone of the sclerotic, and is continuous with the
=iris= (_e_). The choroid coat is furnished in certain parts of its area
with a layer of cells containing crystals, which give it a brilliant
color, forming the =tapetum=. The color of the tapetum is a metallic
yellowish blue or green; it is this layer which causes the cat’s eye to
“shine” in the dark.

The =iris= (_e_) is a continuation of the choroid. It projects inward
from the white zone of the sclerotic, forming a circular curtain lying
some distance behind the cornea, and perforated by an opening, the
=pupil=. The iris is usually yellow in color on its outer surface,
darkly pigmented within. The pupil varies normally in size and form
according to the amount of light to which the eye is subjected. In a cat
killed with chloroform the pupil is very large and circular; in the
living animal it is elliptical with the long axis dorsoventral, or when
much contracted it is a mere dorsoventral slit.

The inner coat of the eye is formed by the =retina= (_g_). This is the
part of the eye which is sensitive to light; it is formed by an
expansion of the optic nerve (_a_). In a preserved eye it is usually
soft and opaque, and may be seen to line the caudal half of the inner
surface, extending apparently to the ciliary body. Here it seems to end
as a free margin, the =ora serrata=; it really becomes thin and passes
onto the surface of the ciliary body, forming the =ciliary portion= of
the retina, and onto the inner surface of the iris, where it forms the
uvea. Near the centre of the retina the entrance of the optic nerve is
marked by a small round spot, the =blind spot=.

The =Crystalline Lens= (_h_).--The lens is a biconvex transparent body
situated within the eye a little in front of the ciliary body and just
behind the iris. It is more strongly convex in front than behind. The
lens is surrounded by a thin transparent sac, the =capsule= of the lens
(capsula lentis). The capsule of the lens is attached all around the
equator of the lens by fibrous bands to the ciliary body, this
attachment forming the =zonula ciliaris= (or zonula Zinni) (_i_), by
which the lens is suspended.

=Chambers of the Eye.=--The lens (_h_) and zonula ciliaris (_i_) form a
partition dividing the eye into two parts. The cavity in front of the
lens contains a fluid, the =aqueous humor=. This cavity is partly
subdivided by the iris into the _anterior_ and _posterior chambers_ of
the eye.

The part of the eye lying behind the lens is much larger than the part
in front of the lens. It is lined chiefly by the retina, its front
boundary being the lens. It contains a jelly-like substance, the
=vitreous humor= (or vitreous body, =corpus vitreum=).


II. THE EAR. ORGANON AUDITUS.

The ear of the cat, like that of man, is composed of three parts, the
external, middle, and internal ear.

The =external= ear is limited internally by the tympanic membrane.

The =middle= ear extends from the tympanic membrane to the fenestra
cochleæ and fenestra vestibuli. It contains the bones of the ear, and is
connected with the pharynx by the Eustachian tube.

The =internal= ear is wholly contained within the petrous bone, and on
the surface of the membrane lining its cavities are distributed the
branches of the auditory (eighth) nerve.

=The External Ear.=

The external ear consists of an expanded portion, the =auricle=
(=auricula=) or pinna, and of a canal leading from the auricle to the
tympanic membrane, known as the =external auditory meatus=. The concave
surface of the auricle is directed craniolaterad, and its edges form the
dorsal and lateral boundaries of the auditory opening. From the bottom
of the cavity which it partly encloses, the external auditory meatus
passes medioventrad.

The auricle (Fig. 168) is composed of a thin curved plate of cartilage
(=cartilago auriculæ=), to which numerous muscles are attached and which
is covered on both sides by integument intimately attached to the
cartilage. Distad the edges of the cartilage form a free border (_b_);
proximad the plate is rolled together in such a way that its edges (_g_
and _h_) overlap on the craniomedial side, thus enclosing a tube or
funnel (_e_) (concha) which forms the enlarged outer portion of the
auditory passage.

Within the cavity of the auricle, on its medial surface, somewhat below
the level of the lowest portion of the margin of the auditory opening is
seen a very prominent pedunculated process (_d_). This is really part of
a transverse ridge, extending craniocaudad on the medial wall of the
auricular cavity. This ridge is the =antihelix= (_d_); it divides the
auricula into a distal and a proximal portion. The portion distad of the
antihelix is the =scapha= (_a_); its surface is smooth except for two
slight longitudinal ridges extending distad from near the two ends of
the antihelix. That portion of the auricle that lies proximad of the
antihelix forms a deep irregular cavity known as the =concha= (_e_). A
deep furrow, corresponding to the antihelix, separates scapha from
concha externally. The concha extends caudad as a deep, rounded pocket;
externally this pocket forms a prominent convexity, the =eminentia
conchæ= (_j_), on the caudal surface of the proximal portion of the
external ear. Farther proximad the concha narrows like a funnel and
becomes much compressed laterally, so that a section of its cavity forms
a narrow craniocaudal slit.

The inner surface of the concha is marked by a number of very prominent
ridges and projections. These are usually due to folds in the cartilage,
so that external furrows and depressions correspond to the internal
projections. The edges of these depressions serve for attachment of
muscles (Fig. 169), by contraction of which the form of the concha is
changed,--the folds of the cartilage thus serving as regions of greater
flexibility.

Two or three centimeters proximad of its external opening the cartilage
of the concha ends in a free edge which receives within itself the
distal end of the cartilaginous external auditory meatus (_e′_). The two
are united together by fibrous tissue. The cartilaginous auditory meatus
(_e′_) extends as a nearly cylindrical tube mediad and slightly craniad
to the tympanic membrane in the opening of the bulla tympani. This tube
is lined with integument which continues over the tympanic membrane. The
subcutaneous tissue of the tube contains the ceruminous glands, which
secrete the ear-wax and open on the surface of the skin.

To understand the relations of the muscles of the external ear it is
necessary to consider a little more fully the structure of the auricular
cartilage (Fig. 168), especially as compared with the human ear. The ear
of the cat differs from the human ear in the fact that the edges of the
auricular cartilages are rolled together proximad so as to overlap.
There is thus no gap between the tragus (_g_) and antitragus (_h_), as
in man, but these two structures partly overlap.

  [Illustration: FIG. 168.--CARTILAGE OF THE EXTERNAL EAR, CRANIOMEDIAL
  VIEW.

  _a_, scapha or pinna; _b_, helix; _c_, spine of the helix; _d_,
  antihelix; _e_, concha; _e′_, cartilaginous auditory meatus; _f_,
  crista helicis; _g_, tragus; _h_, antitragus; _i_, processus
  uncinatus; _j_, eminentia conchæ.]

The free edge (_b_) of the auricular cartilage corresponds partly to the
=helix= of man. At its mediocranial angle the proximal part of the
auricle is composed of muscle and integument only, so that the cartilage
when isolated presents here a deep notch distad of which is a prominent
projecting angle, the =spine= (_c_) of the helix, which serves for
attachment of the adductor auris superior muscle (Fig. 169, 1).
Proximad of the spine, separated from it by the deep notch, the cranial
edge (_g_) of the auricular cartilage approaches the caudal edge (_h_),
finally overlapping it, so that the cavity of the auricle is now
completely surrounded. This overlapping portion of the cartilage is on
the medial side of the cavity, and in the natural state is covered by
muscles and integument, so as not to be apparent.

That portion of the cranial edge of the cartilage that overlaps the
caudal edge forms a cartilaginous plate which projects proximad as a
blunt point; this plate is the =tragus= (_g_). Along the inner edge of
the tragus is a ridge which forms a continuation of the helix; this is
the =crista helicis= (_f_). The portion of the caudal edge of the
cartilage that is partly overlapped by the tragus is an irregular flat
plate known as the =antitragus= (_h_). At its caudolateral margin the
antitragus extends distad as a thin, pointed, cartilaginous spine, the
=processus uncinatus= (_i_). This supports a sheet of integument which
bears two longitudinal ridges projecting into the cavity of the ear,
with a broad groove between them.

=The Scutiform Cartilage.=--Closely connected with the external ear, but
not forming a part of it, is the scutiform cartilage. This lies in the
temporal fossa, between the integument and the temporal muscle, just
behind the orbit and beneath the craniomedial portion of the auricle
(Fig. 63, 1, page 97). It is a narrow cartilage about two centimeters
long, with its long axis craniocaudal. For the greater part of its
length it forms a slender rod, from which a thin cartilaginous sheet
extends a short distance laterad; at its caudal end the rod forks, the
two arms extending nearly at right angles to the main portion. The
scutiform cartilage serves for the origin or insertion of a number of
the muscles of the ear.

=Muscles of the External Ear= (Fig. 169).--(_a_) The muscles connecting
the cartilages of the external ear with other parts of the head have
been described (page 96), excepting the tragicus lateralis (4). These
muscles are the following: M. intermedius scutulorum (Fig. 63, _a_), M.
frontoauricularis, M. levator auris longus (including the
cervicoauricular) (Fig. 63, _g_, _g′_), M. auricularis superior (Fig.
63, _k_), M. abductor auris longus (Fig. 63, _m_), M. abductor auris
brevis (Fig. 63, _l_), M. zygomaticus (Fig. 64, _d_), M. submentalis
(Fig. 64, _c_), M. depressor conchæ (Fig. 64, _b_), M. frontoscutularis,
M. adductor auris inferior (Fig. 63, _f_), and M. tragicus lateralis
(Fig. 169, 4).

=M. tragicus lateralis= (Fig. 169, 4).--A band about seven millimeters
wide, lying beneath the mass of fat about the ear and running ventrad
lengthwise of the concha and close against it.

_Origin_ (Fig. 96, _a_, page 229) on the caudal end of the mandibula, in
the cavity found between the condyloid process and the angular process.
The muscle passes dorsad and is _inserted_ (Fig. 169, 4) on the caudal
margin of the tragus and in the depression on the concha just caudad of
the tragus.

_Relations._--This muscle lies between the temporal muscle and the
concha.

_Action._--Pulls the ear ventrad and probably rotates it outward.

(_b_) The following three muscles connect the scutiform cartilage with
other parts of the external ear.

=M. rotator auris= or =scutuloauricularis inferior=.--A flat
craniocaudal band of fibres lying between the auricle and the temporal
muscle.

_Origin_ on the scutiform cartilage, just caudad of the insertion of the
frontoscutularis, of which this muscle seems to be a continuation. The
muscle passes caudad as a band seven or eight millimeters wide, curving
about the medial surface of the auricle, and is inserted on the
caudomedial surface of the eminentia conchæ.

_Relations._--Lateral surface with the auricular cartilage; medial
surface with the temporal muscle.

_Action._--Rotates the external ear mediad and caudad.

  [Illustration: FIG. 169.--CARTILAGE OF THE EXTERNAL EAR, WITH MUSCLES.

  _a_-_i_, as in Fig. 168. 1, M. adductor auris superior (cut); 2, M.
  adductor auris medius (cut); 3, M. helicis; 4, M. tragicus lateralis
  (cut); 5, 5′, M. tragicus medialis; 6, M. antitragicus; 7, M. adductor
  auris inferior (cut); 8, M. depressor conchæ (cut); 9, M. conchæus
  externus; 10, part of M. auricularis externus; 11, M. abductor auris
  longus (cut).]

=M. adductor auris superior= (Fig. 169, 1; Fig. 63, _f_). (Part of the
auricularis anterior of man.)

_Origin_ on the dorsal surface of the scutiform cartilage for its entire
length. The fibres form a continuation of those of the frontoscutularis;
they pass dorsocaudad and are _inserted_ into the spina helicis or
craniomedial margin of the auricular cartilage. This muscle lies in the
fold of skin that connects the craniomedial angle of the auricular
cartilage with the head, so that it is covered on both sides by
integument.

_Action._--Draws the auricle craniad.

=M. adductor auris medius= (Fig. 169, 2). (Part of the auricularis
anterior of man.)--A very thin band of fibres eight to ten millimeters
broad.

_Origin_ on the middle two-thirds of the caudoventral edge of the
scutiform cartilage. The fibres pass nearly ventrad and are _inserted_
along the medial or caudal surface of the tragus.

_Relations._--Outer surface with the auricular cartilage. Inner surface
with the temporal muscle or with the pad of fat separating this from the
auricle.

_Action._--Pulls the concha dorsocraniad.

(_c_) The remainder of the muscles of the ear interconnect parts of the
auricular cartilage.

=M. transversus auriculæ= (Fig. 63, _i_).--A band about six to eight
millimeters wide, on the medial convex surface of the auricle, between
the distal ends of M. levator auris longus (_g′_) and M. auricularis
superior (_k_).

_Origin_ on the medial surface of the concha, just proximad of the
furrow which corresponds to the antihelix. The muscle bridges this
furrow, passes distad about two centimeters, and is inserted on the
auricular cartilage on a line which forms a caudal continuation of the
line of insertion of the levator auris longus (_g′_).

_Relations._--Outer surface with the levator auris longus (_g_, _g′_),
the auricularis superior (_k_), and the integument; inner surface with
the auricular cartilage.

_Action._--Flexes the scapha mediad on the concha, thus enlarging the
external opening of the concha.

=M. auricularis externus= (Fig. 169, 10; Fig. 64, _r_).--This consists
of small scattered bands of interrupted fibres on the convex surface of
the auricle, caudad of the transversus auriculæ. The largest of these
bands runs parallel with the transversus auriculæ about five or six
millimeters caudad of the latter. It has origin on the eminentia conchæ
distad of the insertion of the abductor auris longus. Thence the fibres
run distad five or six millimeters and are interrupted by an attachment
to the cartilage. Distad the fibres begin again, and the muscle runs
thence distad for about one centimeter, the distal end being attached to
the cartilage.

Caudad of this, especially of its proximal portion, are one or two small
bands of fibres usually running parallel with it, but unconnected with
it and with each other. The extent and distribution of these bands
varies, and the direction of fibres is also variable.

_Relations._--Outer surface with the integument; inner surface with the
auricular cartilage.

_Action._--Flexes the auricular cartilage.

=M. helicis= (Fig. 169, 3; Fig. 64, _m_).--A muscle about two
centimeters in length and five or six millimeters in width, on the inner
surface of the ear, along its cranial margin.

_Origin_ on the medial surface of the concha, just caudad of the
proximal end of the tragus. The fibres pass distad to be inserted on the
auricular cartilage at the caudal angle of the notch which lies beneath
the cranial edge of the auricle, along with the caudal fibres of the
adductor auris superior (1).

_Relations._--Lateral surface with the integument; medial surface with
the tragus.

_Action._--Draws proximad the cranial margin of the auricle.

=M. antitragicus= (Fig. 169, 6; Fig. 64, _n_).--A small muscle about one
centimeter in length and three millimeters in thickness, attached at one
end to the caudal border of the antitragus. The fibres pass mediodistad
and are inserted on the tragus, in common with the fibres of the
tragicus medialis (Fig. 169, 5, 5′).

_Relations._--Outer surface with the adductor auris inferior and the
integument; inner surface with the cartilage.

_Action._--Constricts the external auditory opening.

=M. tragicus medialis= (Fig. 169, 5, 5′).--A small, flat muscle, in two
parts, on the medial surface of the concha.

_Origin_ on the ventral end of the tragus. The cranial fibres form a
thick nearly cylindrical bundle which extends proximad about one
centimeter, and is inserted on the cranial surface of the concha just
proximad of a deep fold in the cartilage. The caudal fibres form a thin
sheet which spreads on the medial surface of the concha and is inserted
on an obliquely proximodistal line on the medial surface of the concha,
less than one centimeter from the free distal edge.

These two bundles are distinct except at their origin, and are sometimes
considered as separate muscles.

_Relations._--Outer surface with the tragicus lateralis (4) and the fat
about the concha. Inner surface with the concha.

_Action._--Flexes the concha.

Strauss-Durckheim describes under the name =cornetoconchæus= a small
muscle bridging the deep groove caused by the folding of the medial
surface of the concha, its proximal end being close to the insertion of
the abductor auris brevis (page 100). This muscle was absent in all of
the cases examined for its presence.

=M. conchæus externus= (Fig. 169, 9).--A quadrilateral muscle on the
lateral surface of the concha. The cranial end of this muscle is
attached to the concha a short distance distad of the antitragus along a
dorsoventral line six to eight millimeters in length; the fibres pass
thence caudodorsad a distance of about one centimeter, where they are
again attached to the concha. The muscle thus bridges a shallow
depression on the lateral surface of the concha.

_Action._--Constricts the concha.

=The Middle Ear.=

  [Illustration: FIG. 170.--TYMPANIC MEMBRANE, VIEWED FROM THE INNER
  SIDE.

  The outer wall of the bulla has been removed, carrying with it the
  tympanic membrane with the malleus and incus; these are now viewed
  from the side that was turned toward the cavity. _a_, bony ring
  forming inner end of external auditory meatus; _b_, _b′_, malleus;
  _c_, tympanic membrane; _d_, incus; _e_, lenticular process; _f_,
  chorda tympani nerve; _g_, cartilaginous support for chorda tympani
  nerve.]

The middle ear is enclosed in a cavity within the tympanic bulla. Its
outer boundary, as well as the inner boundary of the external ear, is
formed by the =tympanic membrane= (Fig. 170, _c._) This is a thin,
semitransparent membrane attached to the bony ring (_a_) surrounding the
inner end of the external auditory meatus. It is oval in outline. Across
the dorsal third of its inner surface runs the handle of the malleus
(_b_), to which the membrane is firmly attached and which by pulling on
the membrane gives it the form of a cone instead of a flat surface. The
apex of the cone is directed mediad.

The middle ear, or =cavum tympani=, is an ellipsoidal cavity situated in
the tympanic bulla. On removing the medial wall of the bulla, a bony
plate is seen separating its cavity into two chambers. This plate of
bone extends in from the lateral wall of the bulla, forming a complete
partition except at the dorsocaudal part, where a notch in the bone
forms a free communication between the two chambers. The lateral
chamber, or tympanum proper, contains the bones of the ear and is
limited externally by the tympanic membrane. At its cranial end is seen
the opening of the =tuba auditiva=, or =Eustachian tube=.

  [Illustration: FIG. 171.--MALLEUS AND INCUS, UNITED IN THE NATURAL
  POSITION.

  1, malleus; 2, incus. _a_, handle of malleus; _b_, neck; _c_, head;
  _d_, process for attachment of tendon of M. tensor tympani; _e_,
  wing-like plate and process of neck; _f_, _g_, the two processes of
  the incus.]

The tuba auditiva, or Eustachian tube, is a cartilaginous tube about one
and a half to two centimeters long, passing from the nasopharynx to the
middle ear and placing these two cavities in communication. The
pharyngeal opening is at about the middle of the length of the
nasopharynx, near the dorsal border of the lateral wall; it is a narrow
slit two or three millimeters long. Thence the tube passes caudolaterad
on the ventral surface of the sphenoid bone, and enters the tympanic
cavity through the opening just laterad of the styliform process of the
tympanic bulla. The tube has a thick, cartilaginous medial wall, while
the lateral wall is thin and formed of connective tissue. The lumen of
the tube is a curved slit in cross-section.

=Bones of the Ear= (ossicula auditus).--There are three small bones in
the middle ear, the malleus (hammer) (Fig. 171, 1), incus (anvil) (Fig.
171, 2), and stapes (stirrup) (Fig. 172).

The malleus (Fig. 171, 1) consists of a slender handle (_a_) with a
small neck (_b_) attached at an angle to the caudal end of the handle.
At the end of the neck is a rounded head (_c_) which articulates with
the incus (2), and together with one part of the incus lies in a small
fossa dorsad of the fenestra vestibuli. From the medial aspect of the
neck extends a short process of bone (_d_) to which is attached the
tendon of the tensor tympani muscle. One side of the neck is produced
into a thin wing-like plate, bearing on its edge a pointed process
(_e_).

The =incus= (Fig. 171, 2) bears much resemblance to a two-fanged molar
tooth. It lies in the fossa with the head of the malleus. Its head or
crown is directed craniad and has a concave surface which articulates
with the head of the malleus. One of the fangs (_f_) extends caudad in
the fossa above mentioned and is held in position by a ligament. The
other fang (_g_) extends ventromediad and articulates with the head of
the stapes. This fang terminates in a minute rounded tubercle known as
the =lenticular process=; this in early stages of development is a
separate bone, the =os lenticulare=.

  [Illustration: FIG. 172. STAPES.

  _a_, head; _b_, base; _c_, process for attachment of the stapedius
  muscle.]

The =stapes= (Fig. 172) has the form of a stirrup, and is the last in
the chain of bones. The small end is termed the head (_a_) and the
broader part the base (_b_). The head of the stapes articulates with one
of the processes of the incus. The base of the stapes fits into the
fenestra vestibuli of the petrous bone and completely closes it. The
stapes is held in position by the stapedius muscle, which is attached to
a minute process (_c_) near the head.

Thus the three bones of the middle ear form a chain which connects the
medial surface of the tympanic membrane with the fenestra vestibuli. As
the fenestra vestibuli forms a portion of the wall of the vestibule, the
vibrations of the tympanic membrane are transmitted through the chain of
bones to the fluid within the vestibule.

=Muscles of the Middle Ear.=

=M. tensor tympani.=--The tensor tympani muscle is a short conical
muscle having origin in a small fossa (Fig. 25, _d_, p. 34) in the
petrous bone dorsocraniad of the fenestra vestibuli. Its very short
tendon passes laterad and is inserted into a projection (Fig. 171, _d_)
on the neck of the malleus.

=M. stapedius.=--The stapedius muscle is a short muscle taking origin
from a fossa (Fig. 25, _f_) in the lateral surface of the petrous bone
caudad of that for the incus. It is inserted into the head of the
stapes.

=The Internal Ear= (Fig. 173).

The internal ear or =labyrinth= is completely enclosed in the petrous
bone. In the dry bone the internal ear communicates with the middle ear
by the fenestra cochleæ and the fenestra vestibuli, which have been
described in the account of the petrous bone (page 33). In the recent
state the fenestra vestibuli is closed by the base of the stapes, while
the fenestra cochleæ is covered by a delicate membrane,--so that the
internal ear forms a closed cavity. It is possible to distinguish a
=bony= labyrinth and a =membranous= labyrinth (Fig. 173), the former
being the cavity in the petrous bone, while the latter is the real
auditory organ, situated within the cavity. The membranous labyrinth
repeats in general the form of the bony labyrinth, so that it will not
be necessary to distinguish the two in our account of the main features
of the structure. The auditory nerve is distributed to the membranous
labyrinth. For an account of the minute structure of this organ
reference should be made to a text-book of general histology or
physiology.

  [Illustration: FIG. 173.--MEMBRANOUS LABYRINTH.

  _a_, vestibule; _b_, cochlea; _c_, external semicircular canal; _d_,
  superior semicircular canal; _e_, posterior semicircular canal; _f_,
  scala tympani; _g_, scala vestibuli; _h_, fenestra cochleæ; _i_,
  fenestra vestibuli.]

The labyrinth (Fig. 173) consists of a cavity, the =vestibule= (_a_),
and connected with this a coiled tube, the =cochlea= (_b_), and the
three =semicircular canals= (_c_, _d_, and _e_).

The =cochlea= (_b_) is situated in the promontory,--the rounded
elevation of the petrous bone extending craniad from the fenestra
cochleæ. It consists of a bony tube coiled spirally about a central
column known as the =modiolus=. The coil has nearly the form of a
snail’s shell, and is somewhat more lengthened in the cat than in man. A
plate of bone, the =lamina spiralis=, incompletely divides the cavity of
the canal lengthwise into two parts, known as =scalæ= (_f_ and _g_). One
of these opens at the fenestra cochleæ (_h_) into the tympanic cavity
(or would so open but for the thin membrane covering the fenestra); this
is known as the =scala tympani= (_f_). The other scala is connected with
the vestibule (_a_) and is known as the =scala vestibuli= (_g_).

The =vestibule= (_a_) is a pyramidal cavity situated mediad of the
caudal end of the cochlea. It is connected with the scala vestibuli of
the cochlea, and with the three semicircular canals. The fenestra
vestibuli (_i_) is an opening in its bony wall, filled in the recent
state by the stapes. On the medial surface of the vestibule are a number
of minute orifices through which the auditory nerve enters.

The =semicircular canals= (_c_, _d_, and _e_) are three curved tubes,
each forming about two-thirds of a circle, and opening at both ends into
the vestibule. They are imbedded in the petrous bone. The planes of the
three tubes intersect nearly at right angles; from their position in man
they have been named =external= (_c_), =superior= (_d_), and =posterior=
(_e_). The external one (_c_) is nearly horizontal in position, and
surrounds the curved fossa (Fig. 25, _f_) for the stapedius muscle,
caudad of the fenestra vestibuli. The superior (Fig. 173, _d_) and
posterior (_e_) are in nearly dorsoventral planes, but at right angles
to each other. The superior (_d_) lies in the ridge forming the caudal
boundary of the appendicular fossa. The posterior (_e_) is situated in a
continuation caudad of the ridge which forms the dorsal boundary of the
internal auditory meatus. One end of each canal is slightly enlarged to
form an =ampulla=. The superior (_d_) and posterior (_e_) canals join at
one end and enter the vestibule by a common opening. One end of the
external canal (_c_) opens into the vestibule so close to one end of the
posterior canal (_e_) that they appear to have a common opening, and
this is commonly stated to be the case; according to Jayne, however, the
openings are really separate. The two remaining ends (of the superior
(_d_) and external (_c_) canals) also enter the vestibule separately, so
that the three canals enter the vestibule by five openings.


III. THE OLFACTORY ORGAN. ORGANON OLFACTUS.

The olfactory organ consists of the olfactory mucous membrane, in the
dorsocaudal part of the nasal cavity. The nasal cavity has been
described in connection with the respiratory system.


IV. THE ORGAN OF TASTE. ORGANON GUSTUS.

The sense of taste is located in the mouth-cavity, especially in the
mucosa of the tongue and the soft palate. The proper organs of taste are
the so-called taste-buds, found on the papillæ of the tongue, the soft
palate, etc. Their exact distribution in the cat has apparently not been
worked out.


V. THE INTEGUMENT. INTEGUMENTUM COMMUNE.

The skin of the cat consists of the usual two layers, the outer
=epidermis= and the inner fibrous =corium=. The skin is particularly
thick and tough about the sides of the neck and face.

The skin is covered almost completely with fine soft hairs. Only the end
of the nose, the pads on the soles of the feet, and the nipples are
without hair. A number of long stiff sensory hairs (vibrissæ) are found
on the upper lip, the cheek, and above the upper eyelid.

The pads on the soles of the feet are cushion-like projections of skin,
composed largely of connective and elastic tissue and fat. There is one
large pad for each foot, and in addition a small pad for each digit.
The fore limb has besides a small conical pad which is situated almost
exactly over the pisiform bone.

The =nails= are horny outgrowths of the epidermis, covering the distal
phalanges.

The =muscles= of the skin are the cutaneus maximus and platysma; these
have been described (page 93). The superficial facial muscles are
differentiations of the skin-muscles.



APPENDIX.

PRACTICAL DIRECTIONS.


The following appendix on the dissection and study of the cat is not
intended as a general treatise on methods of preservation and
dissection, but attempts only to give the application of well-known
methods to the dissection and study of the particular animal with which
the book deals. General methods which are referred to but not described
must be looked up, if unfamiliar, in the manuals of general methods.


_Aids to Dissection and Study of the Cat._--A copy of Jayne’s “Mammalian
Anatomy” should be in the laboratory for reference. Only the volume on
the Bones of the Cat has been issued thus far.

Wilder and Gage’s “Anatomical Technology” will be found very useful for
methods of work.

The plates of Strauss-Durckheim’s “Anatomie du Chat” are exceedingly
valuable for the bones and muscles, and should be in the laboratory if
possible. Outline reproductions of these plates have been published by
H. S. Williams (G. P. Putnam’s Sons, New York, 1875). The use of both
the original plates and the reproductions is made difficult by the
antiquated nomenclature used for the structures figured.


_Method of Use of the Present Directions._--Except in the case of the
Bones, the order of study of the structures is usually not the same as
the order in which they are described. This is of course due to
practical difficulties in dissection. The present directions give the
_order of study_, or at least the order of dissection; of course after
dissection the structures can be reviewed in the logical order given in
the descriptions. But in the first study and dissection, the student is
to use these directions for the _order of work_, while using the body of
the book for the descriptions. It will be necessary therefore to keep
the book opened in two places,--one in the appendix, for the directions;
one in the body of the book, for descriptions. In studying the muscles,
for example, the student will follow the order of dissection given in
the appendix, but as every muscle is dissected he will find, confirm,
and study the description of that muscle given in the body of the book.
Other organs are studied in a similar manner.

Before commencing the study, read that portion of the preface which
explains the use of _terms of direction_ (page VII).

Note that the page on which any figure is found may be determined by
consulting the list of figures given in the Table of Contents.


THE BONES.

The bones will of course be studied from dried specimens. These may be
prepared once for all and kept in the laboratory from year to year. A
number of mounted skeletons of the cat should be at hand; these must be
prepared by some one who has skill in such work.


_Preparation of Separate Bones._--For preparing the separate bones the
liquid-soap process recommended by Wilder and Gage (“Anatomical
Technology,” p. 107) will be found most convenient. This is as follows:
The skin and soft parts are removed as far as possible without injury to
the bones.

Make the following “liquid-soap” mixture:

  Soft water                       2000 cc.
  Strong ammonia                   150 cc.
  Nitrate of potash (saltpetre)    12 grams.
  Hard soap                        75 grams.

Heat these together till a homogeneous mixture is formed. Now immerse
the bone or bones to be cleaned in a liquid composed of four parts water
to one part of the above liquid-soap mixture. Boil forty minutes; pour
off the liquid and renew it. Boil about half an hour longer; then remove
soft parts with fingers, scalpel, and brush. The bones may be boiled as
much longer in the mixture as is necessary to make the soft parts come
away easily. If they are boiled too long, however, the epiphyses will
separate from the bones. This is especially likely to occur in young
skeletons, which must therefore not be boiled so long as the bones of an
old cat.

Skeletons prepared in the following rough way are useful for many
purposes. The entire body of the cat, or a single limb, is placed in the
liquid-soap mixture (after partial removal of soft parts), and boiled
till the muscles may be removed, but the ligaments, holding the bones
together, remain. Clean thoroughly without removing the ligaments, and
allow to dry. The bones are thus held together in their natural
positions. Skeletons so prepared are not elegant, but are frequently
useful.


_Disarticulation of Skulls._--The bones of the skull may be separated as
follows: Clean the skull in the liquid-soap mixture, as above described.
Then fill the cranial cavity with dry rice, beans, corn, or some other
seeds that swell much on imbibition of water. Cork up the foramen
magnum, and place the skull for twelve to twenty-four hours in water.
The swelling of the grain will partially separate the bones at the
sutures. The bones may then usually be separated completely by hand.

Entire skulls, and longitudinal sections, as represented in Fig. 43, p.
60, should be at hand.


_Study of the Bones._--The bones should be studied in the order in which
they are described. No further special directions for their study are
necessary.


_Study of Ligaments._--It will usually not be practicable for each
student to make the dissections and preparations necessary for studying
the ligaments. Rather should these be examined on demonstration
preparations preserved in the laboratory. Such preparations may most
easily be made by using _fresh_ material, and dissecting away muscles
and other tissues, leaving only the ligaments connecting the bones. The
preparations are then preserved in one or two per cent. formalin. It is
difficult to prepare the ligaments satisfactorily on preserved material,
because they do not stand out clearly from other tissues in such
material, so that they are not easily distinguishable.


MUSCLES.


_Preparation and Preservation of Material._--Formalin forms by far the
most satisfactory preservative for anatomical material. It is much
better in almost every respect than alcohol, and has the additional
advantage of being much cheaper.

After injecting with formalin, the cat may be preserved either immersed
in a weaker solution of the same substance, or may be kept for a long
time simply wrapped in a cloth dampened with formalin. The details of
preparation differ according to which method is to be used.

In either case, the cat should be killed with chloroform, by placing it
in a tight jar or box with a cloth or bit of cotton saturated with
chloroform. It is not necessary to bleed the specimen. When the cat is
dead, remove it to a tray, place it on its back, and tie the limbs
loosely so that they will remain outspread.

Expose the femoral artery in the thigh, as follows: Make a median
longitudinal incision through the skin of the abdomen, from a point an
inch or two caudad of the xiphoid process to the pubis. Make an incision
passing from near the middle of this obliquely laterad onto the thigh,
for about three inches. Reflect the two flaps in the angles between
these cuts, then with forceps and tracer isolate the femoral artery just
as it passes into the thigh (Fig. 127, _a_). Make with scissors an
oblique incision in one side of the artery, one-half to one inch from
the point where it leaves the abdominal cavity. Introduce a canula
directed toward the body, and tie it in place.

1. If the cat is to be preserved immersed in a solution of formalin, it
should now be injected with a five per cent. solution of commercial
formalin in ordinary water (commercial formalin 5 parts; water 95
parts). Into an adult cat 300 to 400 cubic centimeters of the five per
cent. formalin should be injected.

The cat may now be preserved in a one per cent. solution of formalin.
Before immersing it in the formalin it is well to remove the hair in
some way, otherwise this will hold much water and be very inconvenient
in dissection. The neatest method is to cut off the hair with scissors;
this takes some time, however. If the skin-muscles (p. 93) are not to be
dissected, the skin may be removed. It is well in this case to leave the
skin on the sides of the head and on the feet.

It is not necessary to open the abdominal cavity, after injecting with
the five per cent. formalin. If there is at any time reason to suspect
that the viscera are not keeping well, the abdominal and thoracic
cavities should be filled with five per cent. formalin by making a small
hole through the body wall into the cavity, introducing a canula, and
injecting till the cavity is full.

The specimen should be kept in a jar or other vessel and should be
completely immersed beneath the one per cent. formalin. Any parts
projecting above the fluid may be attacked by mould. If a part is found
to be moulded, it should be submerged, when the mould will be killed.
The mould injures the specimen if allowed to grow for a long time, but
if discovered soon, no very serious harm results.

During dissection, exposed parts of the body should be kept from drying
by covering with a damp cloth. Specimens preserved in formalin dry out
much less quickly than those preserved in alcohol.

2. For some purposes it is much more convenient to preserve the material
without immersing it in a vessel of formalin. Specimens injected with
five per cent. formalin, as above directed, would usually keep perfectly
without further treatment, but for two difficulties: (1) the specimen
may _dry_; (2) it may be attacked by mould.

The drying may be prevented as follows: Use for injecting a mixture of
the five per cent. formalin with one-sixth its volume of glycerine. This
will dry only very slowly, and if pains are taken to keep exposed parts
covered with cloths dampened with the mixture of formalin and glycerine,
there will be no trouble from this source. The skin should not be
removed from such specimens except as necessary in the course of
dissection. The hair will give little trouble, because dry.

The specimens should be kept in a tight box, that the fluid may not
evaporate rapidly from the cloths used for wrapping.

The attacks of the mould present a difficulty not so easily overcome. As
long as the specimens are in daily use for dissection, and exposed parts
kept covered with cloths saturated with the glycerine and formalin
mixture, little or no trouble is to be anticipated. But if the specimens
are left untouched for some days, and particularly if exposed surfaces
are not kept covered in the manner above recommended, mould is almost
sure to attack them. Material neglected for a week may thus be ruined.

If mould is found at any time to be attacking the material, the attacked
part should be cleaned and well wrapped in cloths saturated in the
formalin-glycerine mixture. If such means are unavailing, the specimen
should be immersed in a vessel of one per cent. formalin and preserved
for the future in this. Recourse should be had at once also to this
method of preservation if the specimen shows signs of decomposition by
having a strong odor.

It seems probable that the attacks of the mould might be prevented by
mixing some fungicide with the injecting fluid; experiments should be
made in this direction.

There are many advantages in preserving the material if possible without
immersing it. All parts retain their color and pliability much more
completely, so that the different structures are much more easily
distinguishable. The method above described, by the use of formalin and
glycerine, is to be recommended when the material is to be worked on
every day or so and is not to be kept longer than a few weeks. It is
usually not very satisfactory in warm weather, however. If some method
can be devised of entirely preventing the attacks of the mould, this
will be an excellent method of preserving anatomical material.

The same specimens used for the study of the muscles will serve also for
the spinal cord and brain if prepared by one of the methods above
described. (For the viscera, blood-vessels, and nerves, other specimens
will have to be prepared; for these, directions are given later.)


_Muscles to be Dissected._--It will probably usually be impossible in a
given course of study to dissect all the muscles of the cat. The
instructor will of course select such as seem most advisable to him. The
following may perhaps be recommended as a good selection for a fairly
extensive course: Muscles of the Fore Limbs (pp. 436-439); Muscles of
the Neck and the Deep Muscles of the Head (pp. 439-441); Muscles of the
Wall of the Thorax and of the Abdomen (pp. 441-442); Muscles on the
Ventral Side of the Neck (p. 442). If the superficial facial muscles
(excluding those of the ear) can be studied from a preparation, this
will be a valuable addition to a course (pp. 434-435).


DISSECTION OF MUSCLES.


_General._--In dissecting muscles a prime requisite of successful
dissection is to keep the muscles _clean_. Fat, connective tissue, etc.,
is to be carefully but thoroughly cleared away from the surface of
muscles and from between them. Frequently when it seems impossible to
distinguish the structures described, all difficulty will vanish as soon
as the dissection is thoroughly cleaned.

In transecting a muscle, work under it completely from one edge to the
other (except in case of very wide muscles), then introduce the scissors
or scalpel, and cut it by a smooth clean cut. Always leave the entire
origin with one-half of the muscle, the entire insertion with the other
half.

The student must be prepared to find in some cases considerable
variations from the conditions described. The descriptions attempt to
give an account of the _usual_ structures, but specimens showing no
variations whatever are undoubtedly rare.


DIRECTIONS FOR DISSECTING THE MUSCLES OF THE CAT.


I. THE SKIN-MUSCLES (pp. 93-96, and Fig. 62).

These will perhaps not usually be dissected. If they are to be
dissected, proceed as follows: Make a ventral median longitudinal
incision of the skin from the cranial end of the manubrium to a point
opposite the crest of the ilium. Connect the cranial end of this
incision with the middle of the lambdoidal ridge by a similar incision
through the skin. Make another incision from the manubrium to the
spinous process of the thirteenth thoracic vertebra. Connect the caudal
end of the first incision by an oblique cut with the root of the tail.
Make another incision from the convexity of the knee-joint along the
fold of skin which connects the hind limb and body, as far as the
incision which leads to the root of the tail. Make an incision
surrounding the base of the forelimb. Now reflect these flaps one at a
time, working in general from the ventral side toward the dorsal middle
line. Take great pains not to take up the thin skin-muscle with the
skin. In this way all of one side of the body will be uncovered. The
cutaneus maximus (Fig. 62, _b_) and a part of the platysma (Fig. 62,
_a_) will be thus exposed. Read and verify the descriptions of these
muscles (pp. 93-96). The cranial portion of the platysma cannot be seen
at this stage, but should be dissected in connection with the muscles of
the face.


II. SUPERFICIAL MUSCLES OF THE FACE AND HEAD (pp. 96-107, and Figs. 63
and 64).

These will perhaps not usually be dissected by the student. They should
be studied on a well-dissected laboratory preparation, if possible. If
they are to be dissected, this should be done if possible on a fresh
specimen, as it is very difficult to dissect them on preserved material.
Proceed as follows:

The skin should be removed with care from the sides and top of the face
and head, without injury to the external ear.

 1. The platysma (p. 95, and Fig. 62, _a_). Determine its cranial
attachments.

 2. The intermedius scutulorum (p. 96, and Fig. 63, _a_).

 3. The corrugator supercilii medialis (Fig. 63, _b_).

 4. The orbicularis oculi (Fig. 63, _c_; Fig. 64, _s_).

 5. The corrugator supercilii lateralis (Fig. 64, _k_).

 6. Notice the frontoauricularis if it exists.

 7. The levator auris longus (Fig. 63, _g_, _g′_). Transect and reflect.

 8. The auricularis superior (Fig. 63, _k_). Transect.

 9. The abductor auris longus (Fig. 63, _m_). Transect.

10. The abductor auris brevis (Fig. 63, _l_). Transect.

11. The epicranius (Fig. 63, _h_, _h′_). In dissecting this muscle the
intermedius scutulorum and corrugator supercilii medialis may be cut by
an incision parallel to the middle line but a short distance to one side
of it.

12. The zygomaticus (Fig. 64, _d_). This and the two following muscles
may usually be best seen running beneath the fibres of the platysma,
without reflecting the latter. If necessary, however, the platysma may
be transected and reflected, though this can be done only with great
difficulty.

13. The submentalis (Fig. 64, _c_).

14. The depressor conchæ (Fig. 64, _b_).

The zygomaticus, submentalis, and depressor conchæ should now be
transected one or two centimeters from the external ear. The
corrugatores supercilii lateralis and medialis may be cut across between
the eye and the ear, and reflected. There is thus exposed:

15. The frontoscutularis. Transect near the scutiform cartilage.

16. The adductor auris inferior (Fig. 64, _o_). Transect near its
insertion.

The external ear is now attached to the head only by the external
auditory meatus and the tragicus lateralis muscle. Read the description
of the latter (p. 418, and Fig. 67, _a_), find it beneath the fat which
surrounds the proximal portion of the external ear, and cut it as far
ventrad as possible. Now cut across the cartilaginous auditory meatus as
near to the tympanic bone as possible, and remove the external ear,
preserving it for future study. (The remainder of the muscles of the
external ear may be studied in connection with the study of the auditory
organ.)

17. The orbicularis oris (p. 105 and Fig. 64, _i_).

18. The zygomaticus minor, if it exists (p. 105, and Fig. 64, _e_).

19. The quadratus labii superioris (p. 105).

  _a._ The levator labii superioris proprius (Fig. 64, _f_).

  _b._ The levator labii superioris alæque nasi (Fig. 64, _g_).

20. The caninus (p. 106, and Fig. 64, _f′_).

21. The buccinator (p. 106).

22. The myrtiformis (p. 106, and Fig. 64, _h_).

23. The “moustachier” (p. 107).

24. The quadratus labii inferioris (p. 107).


III. MUSCLES OF THE FORE LIMB.


A. _Muscles connecting the Arm with the Body._--If the skin-muscles have
been dissected, as above, cut the cutaneus maximus near its insertion,
and reflect it toward the median dorsal line; in this way remove it
completely. Remove the platysma in the same way. The first layer of
body-muscles is thus exposed.

If the skin-muscles are not to be dissected, these may be removed with
the skin. If the skin has not yet been removed, proceed as follows:

Beginning at the cranial end of the manubrium make two incisions in the
skin, one passing to the lambdoidal ridge and the other to the spinous
process of the thirteenth thoracic vertebra. Raise the triangular flap
thus formed, taking up the skin-muscles with it.

 1. The trapezius group of muscles (pp. 115-117, and Fig. 68, _d_, _h_,
and _j_) is now exposed and may be dissected. Begin with the
spinotrapezius (Fig. 68, _j_). Read the description of the muscle, then
raise its caudal border and work under it until its cranial border is
reached and the middle of its inner surface is free. Then transect it,
and reflect the two halves of the muscle toward the origin and
insertion, clearing the fat, etc., from the inner surface of the muscle
and the parts covered by it. Determine origin and insertion.

 2. The acromiotrapezius (Fig. 68, _h_). Dissect in the same manner,
being careful not to injure the broad thin tendon which connects the two
muscles across the middle line.

 3. The clavotrapezius (Fig. 68, _d_). Separate it carefully, from the
cleidomastoid (p. 120). Transect and reflect, as before.

 4. The occipitoscapularis (Fig. 73, _a_, p. 149). Note the strong
fascia which separates it from the deeper muscles of the neck. Be
careful not to injure adjacent muscles in tracing this toward origin
and insertion. Transect.

 5. The rhomboideus. Transect.

Recognize the levator scapulæ ventralis (Fig. 68, _f_), the
sternomastoid (Fig. 68, _c_; Fig. 65, _g_), and the cleidomastoid (Fig.
65, _h_). Then dissect--

 6. The levator scapulæ ventralis (Fig. 68, _f_). Its origin (Fig. 72,
_c_, _c′_) cannot be seen at this stage and should be left until the
cervical muscles are dissected. Be careful in transecting this muscle to
separate it well from the cleidomastoid. Transect.

 7. The cleidomastoid (Fig. 65, _h_). Its origin cannot be fully seen at
this stage. Transect.

Make a midventral incision of the skin from the cranial end of the
manubrium to a point opposite the crest of the ilium. From the caudal
end of this incision make an incision to the root of the tail. From the
cranial end of the incision in the ventral middle line make a cut around
the base of the fore limb on its caudal side, thus connecting the
ventral incision with the incision which passes between the manubrium
and the thirteenth thoracic vertebra.

Make another incision from the convexity of the knee at the joint along
the fold of the skin which connects the hind limb and body, to the
incision which leads to the root of the tail.

Reflect the flaps thus formed so as to expose the body and flank,
removing the skin-muscle with the skin.

 8. The latissimus dorsi (p. 121, and Fig. 68, _m_). Dissect it up and
transect it. Work carefully toward its insertion and note the origin
from its outer surface in the axilla of a part of the cutaneus maximus,
and at about the same place of a thin muscle, the epitrochlearis (p.
164, and Fig. 65, _r_), _without_ determining the insertion of the
latissimus.

 9. Dissect the pectoralis group of muscles (Fig. 65, and p. 144), i.e.,
the pectoantibrachialis (Fig. 65, _m_), the pectoralis major (_l_),
pectoralis minor (_o_), and xiphihumeralis (_p_).

Determine the border of each muscle before lifting it, then work it up
at its middle, transect it, and work toward its ends, determining origin
and insertion.

Refer constantly to the skeleton.

10. Then recognize the teres major (p. 163, and Fig. 75, _d_; Fig. 77,
_c_) and the common insertion of the teres major and latissimus (Fig.
79, _d′_); find the bicipital arch (Fig. 65, _t′_) and determine its
composition (p. 166).

11 and 12. The serratus anterior and levator scapulæ (Fig. 73, _h_ and
_i_, and p. 122). In order to expose the origin of these muscles, the
external oblique muscle (Fig. 68, _p_) must be recognized, and that part
of it which has its origin from the fourth to the ninth rib should be
transected about an inch and a half from its origin and reflected.

The thoracic portion of the rectus abdominis (Fig. 73, _k_) and of the
scalenus (Fig. 73, _f_-_f‴_) should also be recognized and then raised
at their outer borders and displaced toward the median line. _No part_
of any of these muscles should be removed or cut except as directed.

The serratus anterior and levator scapulæ should be transected and
reflected to get at their origin and insertion.


B. _Muscles of the Arm_ (p. 156).--The arm is thus removed from the body
and the dissection may be continued on the separated arm.

13. The clavobrachial (Fig. 65, _k_, and p. 157). Its origin is best
seen later. Dissect it up, but do not transect it.

Search now with great care for the coracobrachialis. Consult the figures
(Fig. 79, _c_) and descriptions (p. 164), and be especially careful not
to injure the long head of the muscle and its tendon.

14. Dissect the coracobrachialis (Fig. 77, _f_). Cut and reflect it.

15. The subscapularis (Fig. 77, _a_, and p. 161). Near its glenoid end,
its glenoid and coracoid borders are separated by triangular intervals
from the adjacent muscles. Transect the muscle by a line connecting the
apices of these triangles. Carry an incision from the middle of this one
to the middle of the vertebral border of the scapula, and reflect the
muscle on both sides of this incision,--thus determining its area of
origin. Reflect the humeral end without injuring the capsule of the
joint.

16. Dissect the supraspinatus (Fig. 75, _a_, and p. 159). Cut the strong
fascia free from the border of the scapula and its spine. Then transect
the muscle and reflect it, being careful not to injure the capsule of
the joint.

17. The spinodeltoideus (Fig. 75, _e_, and p. 156). Find its two
borders, beginning with the caudal one. In freeing the very short
cranial border do not injure the acromiodeltoideus (Fig. 75, _f_).
Transect and reflect the spinodeltoid.

18. The acromiodeltoideus (p. 157, and Fig. 75, _f_). Transect and
reflect.

19. The infraspinatus (p. 160, and Fig. 75, _c_). Locate the borders in
the region of the great scapular notch. It is difficult to separate the
glenoid border from the adjacent teres minor (Fig. 80, _c_). The
separation should be begun at the humerus. Transect the muscle at the
great scapular notch and reflect. Be careful not to injure the teres
minor (Fig. 80, _c_).

20. The teres major (p. 163, and Fig. 75, _d_; Fig. 77, _c_) should be
cut near its junction with the latissimus dorsi (Fig. 77, _e_).

21. The teres minor (Fig. 80, _c_, and p. 161) need not be cut.

22. The epitrochlearis (p. 164, and Fig. 65, _r_).

23. The triceps (p. 166). (_a_) The long head of the triceps (Fig. 77,
_i_; Fig. 75, _g_). Find first its medial border and separate it from
the medial head. Note the union of its lateral surface with the dorsal
border of the lateral head by strong fascia, and then cut the fascia.

(_b_) The lateral head (Fig. 75, _h_).

(_c_) The medial head (Fig. 79, _g_, _h_, and _j_).

24. The anconeus (p. 170, and Fig. 80, _l_).

25. The brachioradialis (p. 173, and Fig. 75, _k_). Reflect it carefully
to its origin and insertion.

26. The biceps (Fig. 77, _g_, and p. 165). The capsule of the
shoulder-joint may be opened in order to expose its origin. Its
insertion cannot be seen at this stage.

27. The brachialis (Figs. 75 and 79, _i_, and p. 166). Work under it
near its union with the clavobrachial; cut it at that point and reflect
it.

28. Extensor carpi radialis longus (p. 173, and Fig. 75, _l_). Note the
oblique tendon on the radial side of the wrist near the insertion of the
brachioradialis. A second tendon passes beneath its distal border. This
tendon may be separated into a deep and superficial portion. The latter
may be traced proximad to its muscle, the extensor carpi radialis
longus.

29. Extensor carpi radialis brevis (p. 174). Its tendon is the deeper of
the two tendons seen when isolating the tendon of the extensor longus.

30. Extensor communis digitorum (p. 174, and Fig. 75, _m_).

31. Extensor lateralis digitorum (p. 175, and Fig. 75, _n_).

32. Extensor carpi ulnaris (p. 176, and Fig. 75, _o_).

33. Extensor indicis (p. 176, and Fig. 85, _c_).

34. Pronator teres (p. 179, and Fig. 77, _q_).

35. Flexor carpi radialis (p. 179, and Fig. 77, _r_). The tendon of the
flexor carpi radialis should not be traced to its insertion until the
deep muscles of the palm of the hand have been dissected.

36. Abductor brevis pollicis (p. 184, and Fig. 77, _w_).

37. Flexor carpi ulnaris (p. 180, and Fig. 77, _t_).

38. Palmaris longus (p. 179, and Fig. 77, _s_). In dissecting this
muscle be careful not to injure the part of the flexor sublimis (Fig.
77, _x_) that rises from its surface (see flexor sublimis, p. 181). Cut
the palmaris proximad of the origin of the flexor sublimis and reflect
it.

39. Flexor sublimis digitorum (p. 181 and Fig. 77, _x_). Trace one or
two of the tendons through the sheaths on the ventral surfaces of the
first phalanges. Cut and reflect the radial portion.

40. Flexor profundus digitorum (p. 181, and Fig. 77, _u_). After
recognizing the parts cut through the tendons of the first and fifth
parts and reflect them to determine their origin. Then cut through the
common tendon so as to reflect the other three parts together. Trace one
or two of the tendons to the distal end of the digit.

41. The supinator (p. 177, and Fig. 85, _b_).

42. The extensor brevis pollicis (p. 178, and Fig. 85, _a_).

43. Pronator quadratus (p. 183, and Fig. 87, _a_).

The insertion of the brachialis and clavobrachial (Fig. 87, _c_) and of
the biceps (Fig. 87, _b_) should now be examined.

There remain to be dissected the small muscles of the palm of the hand.
If these have been injured on the side dissected, the hand of the other
side may be used.

44. The lumbricals (p. 184, and Fig. 88, _f_).

45. The flexor brevis pollicis (p. 184, and Fig. 89, _a_).

46. The adductor pollicis (p. 185, and Fig. 89, _b_).

47. The abductor digiti quinti (p. 185, and Fig. 89, _i_).

48. The flexor brevis digiti quinti (p. 186, and Fig. 89, _h_). Cut and
reflect it.

49. The opponens digiti quinti (p. 186, and Fig. 89, _g_). Cut and
reflect it.

50. The interossei (p. 185, and Fig. 89).


IV. MUSCLES OF THE NECK AND THE DEEP MUSCLES OF THE HEAD.

If the superficial muscles of the head have been dissected according to
the directions above given (p. 434), the skin of the head and neck, and
the external ear, will have been removed, and the specimen is ready for
further study. The parotid and submaxillary glands (Fig. 65, 1 and 2)
should be removed if this has not been done; also the lymphatic glands
(Fig. 65, 3).

If the superficial muscles of the head have not been dissected and are
not to be, remove the skin from the side of the neck, head, and face to
the median dorsal line, removing the thin superficial muscles with the
skin. Remove also the parotid, submaxillary, and lymphatic glands (Fig.
65, 1, 2, and 3), and cut through the ear-muscles and the cartilaginous
auditory meatus (under direction) and remove the external ear. Clean
fat, connective tissue, etc., from the surface of the muscles of the
thorax, neck, and head; then dissect as follows:

 1. The sternomastoid (p. 139, and Fig. 65, _g_). Transect and reflect
it.

 2. The cleidomastoid (p. 120, and Fig. 65, _h_). This has already been
transected; examine now its origin.

Remove the large lymphatic gland beneath the sternomastoid and close to
the tympanic bulla, and clean the surface of the muscles in this region.

 3. The levator scapulæ ventralis (p. 120, and Fig. 72, _c_, _c′_,
_c″_). This has already been cut; study now its origin.

 4. The sternohyoid (p. 140, and Fig. 65, _e_). In raising it begin at
the cranial end and take care not to injure the subjacent sternothyroid
(Fig. 65, _g′_). Transect.

 5. The sternothyroid (p. 141, and Fig. 65, _g′_). Transect.

 6. The stylohyoid (p. 112, and Fig. 65, _d_). Transect.

 7. The digastric (p. 107, and Fig. 65, _b_). Transect, and reflect
completely, to the origin and insertion.

 8. The mylohyoid (p. 114, and Fig. 65, _c_). Transect and reflect.

 9. The geniohyoid (p. 113, and Fig. 67, _g_).

10. The jugulohyoid (p. 113, and Fig. 67, _b_).

(The extrinsic muscles of the tongue (p. 228, and Figs. 67 and 96) may
be dissected at this point, if desired. (_a_) The styloglossus; (_b_)
the genioglossus; (_c_) the hyoglossus. They need not be cut.)

11. The masseter (p. 108, and Fig. 65, _a_). Cut the superficial and
middle layers near their insertions by incisions parallel to the border
of the jaw. Cut the deep layer near its origin. Look for the origin of
fibres of the temporal muscle from the inner surface of the middle
layer.

12. The temporal (p. 110, and Fig. 63, _n_). Clear its outer surface
completely. Cut the temporal fascia transversely and reflect it toward
the insertion of the muscle, with the superficial portion of the muscle.
Cut through the zygomatic arch at its two ends and remove it, dissecting
the fibres of the temporal free from their origin on its inner surface.
Then examine the insertion of the temporal.

(The muscles of the pharynx (p. 232) may be dissected at this point; for
directions, see page 451.)

13. The ceratohyoid (p. 115). To uncover this, the middle constrictor of
the pharynx (Fig. 67, _j_) must be cut and reflected.

Cut the mylohyoid, geniohyoid, genioglossus, and the mucosa of the floor
of the mouth free from the mandible on both sides, so that the tongue
and the floor of the mouth may be drawn ventrad and turned out of the
way, exposing the roof of the mouth (as in Fig. 66, p. 112). Cut through
one side of the pharynx near the ventral surface and turn the tongue
toward the uncut side.

The roof of the mouth is thus exposed. Dissect next--

14. The pterygoid muscles (Fig. 66). Remove the mucosa of the roof of
the mouth, especially at the sides of the soft palate, and the two
pterygoid muscles (p. 111) are exposed. The lower jaw may be removed on
one side to get at their origin.

(The muscles of the soft palate (p. 230, and Fig. 66, _d_ and _e_), and
the superior constrictor of the pharynx (p. 233, and Fig. 66, _f_) may
be observed at this point, if desired.)


V. MUSCLES OF THE WALL OF THE THORAX AND OF THE ABDOMEN.

 1. The scalenus (p. 141, and Fig. 73, _f_-_f‴_). To trace its cervical
portion, cut the trachea and œsophagus just craniad of the first rib,
cut the pharynx and hyoid free from the ventral side of the head and
neck, and remove the pharynx, larynx, œsophagus, and trachea (these
should be preserved for future study of the larynx).

 2. The transversus costarum (p. 150, and Fig. 73, _j_).

 3. The serratus posterior superior (p. 148, and Fig. 73, _l_). Transect
this at about the middle of the muscle-bundles, and reflect it in both
directions.

 4. The serratus posterior inferior (p. 148, and Fig. 73, _n_). Transect
and reflect as in the last.

 5. The external oblique (p. 153, and Fig. 68, _p_). Transect it by an
incision parallel to its tendon of origin and about an inch from it, and
reflect in both directions.

 6. The internal oblique (p. 154, and Fig. 73, _o_). Transect and
reflect as above.

 7. The transversus (p. 155, and Fig. 69, _l_). Requires no further
dissection.

 8. The rectus abdominis (p. 155, and Fig. 73, _k_). Open its sheath by
a longitudinal incision near the linea alba.

 9. The external intercostals (p. 150, and Fig. 73, _m_; Fig. 69, _i_).
To see these, remove the origins of the levator scapulæ and serratus
anterior; also the serratus posterior superior.

10. The internal intercostals (p. 151, and Fig. 69, _k_). To uncover
these, remove the external intercostals from between two or three pairs
of ribs.

11. The transversus thoracis (p. 151). To see this muscle, which lies on
the inner surface of the thoracic wall, it is necessary to cut through
the ribs on one side one or two inches from the sternum, and open the
thorax. The muscle can then be observed directly.

(The levatores costarum will be dissected later.)


VI. MUSCLES ON THE VENTRAL SIDE OF THE VERTEBRAL COLUMN IN THE NECK
REGION (Fig. 72).

Clean the surface of these muscles, removing pharynx, larynx, œsophagus,
and trachea, if this has not been done.

 1. Longus capitis (p. 142, and Fig. 72, _a_).

 2. Longus colli (p. 144, and Fig. 72, _g′_, _g″_).

 3. Levator scapulæ ventralis (p. 120, and Fig. 72, _c′_, _c″_). Observe
its origin.

 4. Rectus capitis anterior minor (p. 143, and Fig. 72, _b_). To see
this, cut through on one side the longus capitis and one head of the
levator scapulæ ventralis, and remove the proximal portions, as in Fig.
72.

 5. Obliquus capitis superior (p. 136, and Fig. 72, _e_).

 6. Rectus capitis lateralis (p. 143, and Fig. 72, _d_).


VII. MUSCLES OF THE BACK (p. 123).

Remove what remains of the dorsal portion of the latissimus dorsi,
serratus posterior superior, and serratus posterior inferior. See that
the skin is removed completely to the dorsal middle line, or even for a
little distance over onto the other side. There is thus exposed the
lumbodorsal fascia (p. 126), covering the muscles of the back.

Cut the superficial layer of the lumbodorsal fascia (that from which the
latissimus dorsi and obliquus externus abdominis have origin) by an
incision parallel to the dorsal median line, and remove it. The muscles
of the back are thus exposed (Fig. 69). Observe in the lumbar region the
longissimus dorsi (_f_, _f′_, _f″_); in the thoracic region the
longissimus dorsi, the spinalis dorsi (_g_), and the iliocostal (_h_);
in the cervical region the splenius (Fig. 73, _b_).

 1. The longissimus dorsi (p. 126, and Fig. 69, _f_, _f′_, _f″_). Notice
in the lumbar region the strong deep layer of the lumbodorsal fascia, by
which this muscle is covered, and from the under side of which many of
the fibres of the muscle take origin. Cut this fascia by an incision
parallel to the dorsal median line and about two centimeters from it,
from the level of the crest of the ilium as far craniad as the fascia
can be cut without cutting into the muscle-fibres (usually to about the
level of the last rib). Reflect the medial division of the fascia to the
middle line. Reflect the lateral division of the fascia until it passes
into the muscle and cannot be farther reflected.

Observe then in the lumbar region the medial (Fig. 70, _a_) and lateral
(Fig. 70, _b_) divisions of the longissimus dorsi, and the portion
(_b′_) of the lateral division taking origin from the lumbodorsal fascia
(_c_). Dissect apart some of the muscle-fibres of the longissimus and
observe their origin and insertion.

Trace the longissimus dorsi into the thoracic and cervical regions (Fig.
69, _f′_, _f″_) noting the separation off from it on the dorsal side of
the spinalis dorsi (Fig. 69, _g_); on the ventral side of the iliocostal
(Fig. 69, _h_).

 2. The extensor caudæ lateralis (p. 137, and Fig. 70, _f_). Uncover
this by cutting the lumbodorsal fascia over the sacral region.

 3. The iliocostalis (p. 128, and Fig. 69, _h_). Uncover this
completely; note its connection with the longissimus dorsi at the caudal
end. Dissect apart some of its muscle-bundles, to see origin and
insertion.

 4. The splenius (p. 131, and Fig. 73, _b_). Transect this by an
incision beginning at its lateral border about four centimeters from the
cranial end of the muscle and extending obliquely craniodorsad to the
craniomedial angle of the muscle. Be careful not to injure the
longissimus capitis (Fig. 73, _g_).

 5. The longissimus capitis (p. 131, and Fig. 73, _g_). Transect.

 6. The spinalis dorsi (p. 129, and Fig. 69, _g_). Separate some of its
muscle-fibre bundles and trace to origin and insertion.

 7. The biventer cervicis (p. 132, and Fig. 69, _a_). Raise its lateral
border, turning it toward the middle line, and transect it near its
caudal end.

 8. The complexus (p. 133, and Fig. 69, _b_). Raise its medial border,
and transect it near its cranial end.

 9. The longus atlantis (p. 134, and Fig. 71, _f_).

10. The multifidus spinæ (p. 130, and Fig. 70, _d_). Remove a part of
the longissimus dorsi in the lumbar region, and trace the course of the
fibres of the multifidus spinæ. (If desired the entire longissimus may
be removed and the multifidus spinæ completely uncovered.)

11. The extensor caudæ medialis (p. 136, and Fig. 70, _e_).

12. The semispinalis cervicis (p. 133, and Fig. 71, _c_). Dissect apart
some of its fibre-bundles to see origin and insertion.

13. The interspinales and intertransversarii (p. 131) may be seen in the
region from which the longissimus dorsi was removed, by removing the
bundles of the multifidus spinæ.

14. The rectus capitis posterior major (p. 134, and Fig. 71, _a_).
Transect.

15. The obliquus superior (p. 136, and Fig. 71, _e_).

16. The obliquus capitis inferior (p. 136, and Fig. 71, _b_).

17. The rectus capitis posterior medius (p. 135). Transect.

18. The rectus capitis posterior minor (p. 135).

19. The levatores costarum (p. 150). Remove in a part of the thoracic
region a portion of the iliocostal and longissimus dorsi, so as to
expose the dorsal ends of the ribs. The levatores costarum will be seen
as but slightly separated bundles continuous with the external
intercostals.


VIII. MUSCLES OF THE HIND LIMBS (p. 186).

Remove the skin and superficial fascia from the lateral surface of the
thigh. Examine the _fascia lata_ (p. 186, and Fig. 68, _z_). Dissect:

 1. The biceps femoris (p. 194, and Fig. 68, _t_). Work under its
cranial and caudal borders. Find the tenuissimus (Fig. 90, _g_) passing
obliquely beneath it and reaching its caudal border in its distal half.
Transect the biceps without injuring the tenuissimus, and reflect its
halves.

 2. The tenuissimus (p. 195, and Fig. 90, _g_). Transect.

 3. The caudofemoralis (p. 195, and Fig. 68, _s_). Transect.

 4. The gluteus maximus (p. 187). Transect.

 5. The sartorius (p. 197, and Fig. 68, _q_; Fig. 91, _a_). Transect.

 6. The tensor fasciæ latæ (p. 187, and Fig. 68, _r_). Cut the fascia
lata along the distal end of the muscle-fibres and reflect the muscle.

 7. The gluteus medius (p. 188, and Fig. 90, _b_). Work under it
carefully, separating it from underlying muscles; cut it close to its
tendon of insertion, and reflect it.

 8. The pyriformis (p. 188, and Fig. 163, 7, p. 401). Cut and reflect
it.

 9. The gemellus superior (p. 189, and Fig. 163, 6). This and the next
muscle will sometimes be found to be completely united. Transect.

10. The gluteus minimus (p. 189, and Fig. 163, 5). Transect.

11. The obturator internus (p. 192, and Fig. 90, _e_). Cut it at the
dorsal border of the ischium in order to reflect it. The whole origin
cannot be seen at this stage.

12. The gemellus inferior (p. 190).

13. The gracilis (p. 198, and Fig. 91, _b_). Transect.

14. The semitendinosus (p. 196, and Figs. 90 and 91, _j_; Fig. 92, _i_).
Transect.

15. The semimembranosus (p. 196, and Figs. 90 and 91, _i_; Fig. 92, _h_,
_h′_). Transect.

16. The adductor femoris (p. 198, and Figs. 90 and 91, _h_; Fig. 92,
_g_). Transect.

17. The quadratus femoris (p. 191, and Fig. 90, _f_). Transect.

18. The obturator externus (p. 191).

19. The adductor longus (p. 199, and Fig. 92, _f_). This and the
following will sometimes be found to be almost completely united.
Transect.

20. The pectineus (p. 200, and Fig. 92, _e_). Transect.

21. The iliopsoas (p. 193, and Fig. 91, _c_; Fig. 92, _d_). Only its
distal part, near the insertion, can be seen at present.

22. The capsularis (p. 190). Transect.

23. The quadriceps femoris (p. 201). Isolate the rectus femoris (Fig.
92, _b_) as far as its junction with the vastus lateralis; cut it at
this point and reflect its proximal portion. Turn aside the distal end
and find beneath it the transverse aponeurosis between the vastus
medialis and the vastus lateralis, and covering the vastus intermedius.
The vastus lateralis (Fig. 90, _d_) may be cut near the middle and
dissected up from its origin in both directions; the vastus intermedius
is thus exposed. The vastus medialis (Fig. 92, _c_) and the vastus
intermedius need not be cut.

24. The gastrocnemius (p. 203, and Fig. 90, _m_; Fig. 91, _k_). It may
be raised cautiously near its middle and divided. Care should be taken
not to divide the underlying plantaris (Fig. 90, _l_). After noting the
connection of the outer head with the plantaris, the latter may be
divided and reflected, together with the outer head.

25. The plantaris (p. 205, and Figs. 90 and 91, _l_).

26. The flexor brevis digitorum (p. 212). In tracing its tendon note the
three branches of the common plantar ligament which emerges from between
the second and third tendons. The outer branch is inserted into the
fascia covering the base of the fifth digit, while the other two spread
out into the bilobed pad of the sole.

27. The soleus (p. 205, and Fig. 90, _o_). Cut and reflect.

28. The popliteus (p. 206, and Fig. 92, _k_). Cut very near the origin
and reflect.

The three following deep muscles on the ventral surface of the shank are
covered by the deep crural fascia (p. 206) which separates them from the
overlying muscles. It should be removed.

29. The flexor longus hallucis (p. 207, and Fig. 91, _m_). Divide the
muscle at its junction with the tendon. Open the canals on the
astragalus and calcaneus and reflect the tendon, cutting the tendon of
the flexor longus digitorum near its insertion and dividing at the
middle the quadratus plantæ (p. 213) which may be found inserted into
its ventral surface.

30. Flexor longus digitorum (p. 208, and Fig. 91, _n_). This may be
divided very near its origin.

31. Tibialis posterior (p. 208, and Fig. 91, _o_). This may be divided
near its tendon.

32. Peroneus longus (p. 209, and Fig. 90, _q_). The overlying tendons
may be cut in tracing its insertion.

33. Peroneus brevis (p. 210, and Fig. 90, _s_).

34. Peroneus tertius (p. 210, and Fig. 90, _r_).

35. Extensor longus digitorum (p. 210, and Fig. 90, _p_).

36. Tibialis anterior (p. 211, and Fig. 90, _n_).

37. The extensor brevis digitorum (p. 212, and Fig. 90, _u_).

38. The quadratus plantæ (p. 213). It was cut in dissecting the flexor
longus hallucis.

39. The lumbricales (p. 213).

40. The interossei (with the muscles of the fifth digit) (p. 214).

41. The tarsal muscles (p. 215). The overlying ligaments must be removed
in order to expose the scaphocuneiform.


IX. THE DIAPHRAGM AND THE MUSCLES ON THE VENTRAL SIDE OF THE VERTEBRAL
COLUMN IN THE LUMBAR AND PELVIC REGIONS.

Remove the ventral and lateral walls of the thorax completely, as far
back as the diaphragm,--leaving only a ring attached to the margin of
the diaphragm. Remove the abdominal walls in the same way, as far back
as the pubis, leaving the diaphragm in position. Remove the thoracic
viscera (the heart and lungs may be preserved for future study). Remove
also the abdominal viscera as far back as the beginning of the pelvis,
cutting the large intestine where it passes into the pelvis. The dorsal
wall of the abdominal cavity should be cleared of fat, blood-vessels,
etc., without injury to the crura of the diaphragm.

 1. The diaphragm (p. 151, and Fig. 74). Study by transmitted light, to
see the tendons, etc.

 2. The psoas minor (p. 139, and Fig. 162, 9, p. 398). Find its tendon
and separate it from the iliopsoas (Fig. 162, 8) as far craniad as this
can be done without tearing the fibres.

 3. The iliopsoas (p. 193, and Fig. 162, 8). Find both portions; isolate
them as far as it can be done.

 4. The quadratus lumborum (p. 139). Free the lateral edge of the
iliopsoas from the abdominal wall and turn the whole muscle mediad as
far as possible. The bundles of the quadratus lumborum will be found
beneath it, against the transverse processes of the lumbar vertebræ.

With a heavy cartilage-knife separate the two innominate bones along the
pelvic symphysis. This is easily done if the knife is inserted exactly
into the line of junction of the two bones. Divaricate the edges some
distance, so as to make a ventral opening into the pelvic cavity. If
necessary, part of the innominate bone of one side may be removed to
make the opening larger.

Find the thin sheet of fibres forming the levator ani muscle (Fig. 162,
11) at the side of the rectum, attached to the edge of the symphysis.
Carefully free the rectum and urogenital organs from this and remove
them as far as the anus, leaving the levator ani intact.

 5. The iliocaudalis (p. 137, and Fig. 162, 11′).

 6. The levator ani (p. 269, and Fig. 162, 11).

Remove with great care the levator ani and iliocaudalis of one side, by
cutting first the attachment to the symphysis and the ilium, turning the
muscle mediad, then cutting the attachment to the tail. There are thus
exposed on the lateral wall of the thorax the medial surface of the
obturator internus, craniad of it the pyriformis, caudad of it the
quadratus femoris. Dorsad of these is the abductor caudæ internus.

 7. The abductor caudæ internus (p. 137).

On the ventral surface of the tail are exposed the following:

 8. The flexor caudæ longus (p. 138, and Fig. 162, 12).

 9. The flexor caudæ brevis (p. 138, and Fig. 162, 13).


X. MUSCLES OF THE TAIL (p. 136).

By removing the skin of the tail, all the muscles of the tail are now
easily seen.

 1, 2, 3, 4, 5--see 5, 6, 7, 8, 9, above (IX).

 6. The abductor caudæ externus (p. 137, and Fig. 113, _b_; Fig. 70,
_g_).

 7. The extensor caudæ lateralis (p. 137, and Fig. 70, _f_).

 8. The extensor caudæ medialis (p. 136, and Fig. 70, _e_).


THE VISCERA.

Kill the specimen with chloroform and inject with the five per cent.
formalin, or the mixture of formalin and glycerine, as for the muscles.
(It is an advantage if the preliminary examination of the viscera can be
done in a perfectly fresh, uninjected specimen; such a specimen can be
kept but a day or two, however. After one day’s examination the skin may
be removed and the specimen placed in two per cent. formalin; it will
usually be fairly well preserved by this, though the formalin is too
strong to make the later dissection pleasant. The specimen cannot be
preserved in this manner unless the skin is removed, and a sufficient
quantity of formalin used.)


PRELIMINARY EXAMINATION OF THE VISCERA.

(In this preliminary examination the descriptions in the text need not
be read, except when this is specially directed.)

Wet the hair along a line from the symphysis of the jaw to the pubis.
Part it and make a longitudinal incision through the skin along the
line. Make a transverse incision of the skin five centimeters caudad of
the xiphoid process and reflect the flaps. Incise the body wall from the
last rib to the pelvis along the same line as above and also
transversely. Reflect the flaps without injuring the ligaments of the
bladder. Make an incision through the pectoral muscles between the first
rib and the ventral attachment of the diaphragm and about one centimeter
from the median line. Make a second incision of the muscles from the
cranial end of the first incision along the angles of the ribs to near
the dorsolateral attachment of the diaphragm. Cut the ribs and thoracic
wall along these incisions with strong scissors; connect the two
incisions at their caudal ends, and remove the lateral thoracic wall
thus circumscribed. Note the thoracic and abdominal cavities, separated
by the diaphragm.

Note the following viscera in their fresh condition:

A. In the abdominal cavity (without injuring anything)

 1. The liver, dark red and lobed, in the cranial part of the cavity,
lying against the diaphragm.

 2. The gall-bladder partly imbedded in the right median lobe.

 3. Displacing the liver craniad, the stomach is seen dorsad of its left
lobe. It may extend dorsad of the right lobe, its size depending on the
degree of distension.

 4. The duodenum or first part of the small intestine leaves the stomach
at its right side craniad and makes a U bend, the head of which is
directed caudad; it then turns toward the middle line dorsad of the
remaining part of the small intestine.

 5. The great omentum is a thin fold of peritoneum with many bands of
fat. It passes like a curtain from the great curvature of the stomach
ventrad of the coils of the small intestine (ileum). It is tucked
beneath the mass of coils at the sides and caudally, and folds of it
extend between the individual coils. Turn it craniad and note--

 6. The numerous coils of the third part of the small intestine or
ileum. Turn these to one side and note--

 7. The connection of the ileum with the duodenum across the middle
line. An indefinite part of the intestine between the ileum and duodenum
is called the jejunum, because in man it is found empty after death.

 8. The passage of the ileum into the side of the large intestine which
begins on the right side just caudad of the loops of the duodenum. The
first part of the large intestine is the colon. It may be traced first
toward the head (ascending colon), then sinistro-caudad (transverse
colon) and then caudad (descending colon). The descending colon returns
to the middle line and the large intestine then continues to the anus as
the rectum.

The blind pouch of the colon which lies caudad of the opening of the
ileum is the cæcum.

 9. Turn the duodenum toward the left and note the pancreas, a light
red, elongated organ which stretches along the greater curvature of the
stomach and thence between the two lines of the duodenal U to its
bottom.

10. The spleen, parallel to the gastric portion of the pancreas. It is
deep red (darker than the pancreas and not so brown as the liver) and is
held against the great curvature of the stomach by a part of the great
omentum.

11. The kidneys, close against the dorsal body wall and in contact with
the caudal part of the liver.

12. The bladder, in the median line at the caudal end of the cavity,
held in place by the suspensory ligament, which passes to the midventral
line, and by the lateral ligaments.

13. The mesenteric glands, large grayish-red glands one to four
centimeters long, more numerous in the mesocolon.

14. In the female, lying against the ventral surface of the rectum, the
uterus. It divides into two horns which diverge. Near the end of each
horn the ovary.

15. The peritoneum. Study and understand the description of it (p. 218).
Dissect some of it free from the body wall. (Trace the folds by aid of a
diagram and model.)

B. In the thoracic cavity:

 1. The lungs. Each is divided into lobes, three on the left, four on
the right. The caudal right lobe pushes the mediastium toward the left
and thus lies in a pocket dorsocaudad of the heart and dorsad of the
vena cava inferior.

 2. The pleuræ. Each pleura is a membrane like the peritoneum. It covers
the diaphragm and the thoracic walls and is reflected onto the lungs.
Hence it is divided into costal and pulmonary portions. Read the
description (p. 217) and trace their connection. Each pleura forms a
closed sac.

 3. The mediastinal septum or median vertical portion formed by the
apposition of the medial walls of the two pleural sacs. It divides the
thorax into halves.

 4. In the mediastinum or space between the halves of the mediastinal
septum are seen--

_a._ Ventrally (i.e., in the anterior mediastinum), blood-vessels and
fat, and craniad the pink thymus gland. Read the description of the
thymus (p. 254, and Fig. 107).

_b._ Dorsally (i.e., in the posterior mediastinum) the trachea (best
seen craniad), the œsophagus (best seen caudad), and the aorta.

_c._ In the middle (reckoning in a dorsoventral line) (i.e., in the
middle mediastinum) the heart, with the inferior vena cava approaching
it from the rear. Prick into the mediastinum and inflate it. Remove the
thoracic wall opposite the one already removed, so as to stretch the
mediastinum and show it more clearly. Expose the trachea beneath the
caudal end of the sternomastoidei. Note the thyroid gland (Fig. 96, 6,
p. 229). Insert a blowpipe without injury to the thyroid, and inflate
the lungs. Cut the sternum at its caudal end and turn it craniad,
cutting the mediastinal septum and noting its double character.

Dissect the mediastinal septum from the thymus so as to expose this
organ.

_d._ The pericardium, a relatively thick-walled sac, within which the
heart lies. The pericardium is covered by the mediastinal septum on each
side, but not dorsally and ventrally. Dissect the mediastinal septum
from the pericardium. Prick and inflate the pericardium. Open it and
expose the heart.


DISSECTION OF THE ALIMENTARY CANAL.

Study and verify the descriptions of the organs as they are dissected.

I. Salivary glands (p. 223).

 1. Keep the mouth open by a cork between the teeth. Find the papillæ
upon which open the sublingual and submaxillary ducts (pp. 223 and 224);
remove the mucosa and enlarge the opening and insert a black bristle
into either duct. Trace the duct by the bristle as far as possible on
the floor of the mouth.

 2. Find the white ridge formed on the cheek by the parotid duct (p.
223). It is opposite the molar tooth, and at its cranial end the opening
of the duct is seen. Enlarge the opening and insert a black bristle as
far as possible.

 3. Remove the skin and the skin-muscles from the side of the face,
beginning at the caudal end and working craniad. At the cranial border
of the carotid on the ventral side look carefully for the parotid duct
with the bristle in it. The duct is then easily traced by the removal of
the skin and muscles. Study the parotid gland (Fig. 131, 10, p. 322).

 4. Remove the facial vein (Fig. 131, _b_ and _c_) and lymphatic gland
(Fig. 131, 12) covering the submaxillary gland (Fig. 131, 11) and clean
its outer surface. Raise it and find the submaxillary duct leaving its
inner surface. Reflect the digastric and mylohyoid muscles and trace the
duct to the oral mucosa. The remainder of its course is shown by the
bristle on the inside of the mouth.

 5. The sublingual gland is uncovered in dissecting the submaxillary.
Its duct is seen by the side of the submaxillary. It may be pricked near
the gland and a bristle passed to its opening.

 6. The infraorbital gland. Expose it by removal of the zygomatic arch
and masseter muscle. Find its duct by dissecting apart the lobules at
its ventral end. Prick the duct and insert a bristle to find its inner
opening.

 7. The molar gland. Find it by raising the orbicularis oris of the
lower lip. By raising its ventral border and dissecting between it and
the mucosa the ducts may be found and perhaps pricked and bristles
inserted.

II. The mouth-cavity. Study the general description (p. 221); the lips
and the cheek. Then remove the masseter muscle and the caudal part of
the zygoma. Cut through the mandible between the first premolar and the
canine tooth. Then disarticulate the mandible, cut the cheek and also
the mylohyoid muscle and oral mucosa parallel to the medial border of
the mandible, and remove the mandible with the parts thus left attached
to it. The organs in the mouth-cavity are thus left exposed and should
be studied. To demonstrate the incisive ducts (p. 222) pass a bristle
into them.

The teeth (p. 224). These should be studied on a skull in which the
roots of the teeth have been laid bare by means of the bone-forceps, as
in Figs. 93 and 94.

The tongue (p. 226, and Fig. 95). Study its dorsal surface, the papillæ,
etc. Then dissect its _muscles_ (p. 228) from the ventral side. The
stylohyoid, digastric, and mylohyoid muscles must be removed. Then
dissect (_a_) the styloglossus (Fig. 96, _e_), (_b_) the genioglossus
(Fig. 96, _f_), (_c_) the hyoglossus (Fig. 96, _h_). Make a transverse
section of the tongue to see the intrinsic muscle-fibres.

III. The thyroid gland (p. 254, and Fig. 96, 6). Clean the sternomastoid
muscles. Cut their interdigitating portions along the median line and
reflect them. Find the lateral lobe of the thyroid gland beneath the
lateral borders of the sternohyoid muscles. Dissect it, being careful
not to destroy the delicate isthmus.

IV. The pharynx (p. 231). Remove the large lymphatic gland between the
atlantal transverse process and the larynx. Clean the outer surface of
the pharynx. Dissect the muscles of the pharynx (p. 232) as follows:

  (_a_) The inferior constrictor (Fig. 96, _k_).

  (_b_) The middle constrictor (Fig. 96, _j_).

  (_c_) The glossopharyngeus (Fig. 96, _i_).

  (_d_) The stylopharyngeus (Fig. 96, _l_).

The superior constrictor cannot well be seen at this point; it will be
examined later.

Disarticulate the cranial cornu of the hyoid from the bulla tympani and
make an incision the length of the lateral wall of the pharynx so as to
expose its cavity; study. Examine its opening into the mouth-cavity and
study the general description (p. 231). Find and study the soft palate
(p. 230). Dissect the tensor and levator palatini muscles (p. 230, and
Fig. 66, _d_ and _e_, p. 112), using, if necessary, the specimen on
which the other muscles were dissected. Then slit the soft palate
lengthwise at one side of the median line to expose the nasopharynx (p.
231). Bring the choanæ into view by use of a bit of mirror-glass. Pass a
bristle into the nares and out at the choanæ. Pass a bristle through the
Eustachian tube into the middle ear.

V. Œsophagus (p. 234). After completing the study of the pharynx, leave
the larynx and lungs in position and by displacing them toward the right
follow the œsophagus to its termination. Open it to see the folds of the
mucosa.

VI. Cut through the duodenum at its distal end and through the duodenal
mesentery so as to separate the stomach and duodenum, with the liver,
pancreas, and spleen, from the remainder of the alimentary canal. Float
the parts in a dish of water.

VII. Study the stomach (p. 234, and Fig. 97). Cut out the ventral wall
of the stomach and wash it out, so as to study its cavity, and then
continue the cut so as to expose the pyloric valve (p. 235).

VIII. Study the duodenum (p. 236). Cut away the ventral walls of the
duodenum far enough to expose the ampulla of Vater.

IX. Study the liver (p. 239, and Figs. 100 and 101). Expose the hepatic
duct of the left lateral lobe near its entrance into the lobe, and
follow it so as to expose it fully. If necessary, prick it and inflate
with blowpipe in order to follow it. Then expose the cystic duct and
other hepatic ducts and follow them to or from the common bile-duct.
Trace the latter to the duodenum. If the air does not enter any duct
readily, it may be made to do so by manipulating the duct so as to break
up the precipitated bile which obstructs it.

X. Study the pancreas (p. 241, and Fig. 102). Expose the pancreatic duct
near its entrance into the ampulla of Vater, by removing the peritoneum
from the pancreas just caudad of the end of the common bile-duct, and by
dissecting apart the pancreatic lobules until the duct appears. (If
possible, expose also the accessory duct in the same way on the ventral
side of the pancreas, two centimeters caudoventrad of the ampulla of
Vater. Prick and inflate. Trace its connection with the main duct. To
demonstrate its opening pass a bristle through an opening in it into the
duodenum.) (The pancreatic duct may be injected, if desired.)

XI. The ventral wall of the duodenum should now be removed. Cut out a
small piece, clean its mucosa with a fine brush and examine the villi
with a lens. Demonstrate the coats of the duodenal wall by stripping
them off with forceps.

XII. The ampulla of Vater (p. 236). Pass bristles through openings in
the common bile-duct and pancreatic duct into the duodenum through the
ampulla. Slice away the duodenal wall parallel to the bristles until the
bristles are exposed.

XIII. The spleen (p. 242, and Fig. 102).

XIV. Cut the mesentery from the small intestine and colon and slit them
both lengthwise, but do not destroy the ileocolic valve. Wash and brush
the mucous membrane clean and study the villi, solitary glands, and
Peyer’s patches. Study the ileocolic valve (Fig. 99) and open it to
study its inner surface.


DISSECTION OF THE ORGANS OF RESPIRATION.

I. The nasal cavity (p. 243). Review the description of the nasal cavity
given under the Bones (p. 59). Study the cartilaginous framework that
supports the external nose (p. 243); make a cross-section of the
framework near the end of the nose and verify the description (p. 244,
and Fig. 103). Without injuring the larynx or tongue saw through the
head in a vertical plane and a little to one side of the median line.
(If desired, the brain may first be removed from the specimen and
preserved for future study. For directions, see page 462. The removal of
the brain does not injure the head for the study of the nasal cavity;
the skull may be sawn lengthwise in the same way as before.) Wash out
the cut surfaces before examining. Find the ventral conchæ (p. 40), the
labyrinths of the ethmoid (p. 43), the inferior meatus of the nose (p.
243), and by bristles the lachrymal duct or canal (p. 245). The
lachrymal duct is conveniently found by passing bristles into the
openings of the lachrymal canals. One of these is to be found on the
border of each eyelid, two or three millimeters from the inner angle of
the eye (see p. 410).

Cut the œsophagus and trachea at the point where the blowpipe was
inserted into the trachea. Separate the tongue, hyoid, larynx,
œsophagus, and first part of the trachea from the adjacent parts and
remove them.

II. The larynx (p. 246). (1) Read the description, studying the
cartilages (p. 247) on a preparation (Fig. 104). Then very carefully
remove the pharynx and its constrictor muscles, the sternothyroid and
remains of sternohyoid muscles, and (2) dissect the muscles of the
larynx (p. 249, and Fig. 105). Dissect all those of one side first. The
mucosa lining the vestibule and middle portions of the laryngeal cavity
must be removed. After studying the muscles, remove the muscles and
entire mucosa by scraping carefully with a dull but smooth scalpel, and
study the cartilages (Fig. 104).

III. The trachea and lungs (p. 251, and Fig. 106). The distal end of the
trachea and lungs may now be removed with the heart from the body. The
lungs may be inflated with the bellows. The bronchi should then be
exposed, cleaned, and followed as far as possible into the lungs. The
heart should be preserved for future study.


DISSECTION OF THE UROGENITAL ORGANS.


A. _Excretory Organs._

 1. Expose the kidney (p. 255, and Fig. 108) by removal of the
peritoneum and the surrounding fat, taking care not to open the capsule
of the kidney. In removing the fat from the cranial end do not injure
the suprarenal body (p. 257), which should be studied.

 2. Open the capsule of the kidney and slice away its ventral wall to
expose the sinus. After dissecting the contents of the sinus open the
pelvis and study the papilla. Pass a bristle from the pelvis into the
ureter.

 3. Make a median section of the kidney parallel to its ventral surface
and study structure (Fig. 109).

 4. Trace the ureter to the bladder, being careful not to injure the vas
deferens. Study the bladder and its ligaments, structure of its wall,
etc. Pass a bristle through the ureter into it and then open it to see
the openings of the ureter. Trace the neck of the bladder to the pubis.


B. _Male Genital Organs._

 1. Study the external genital organs (p. 257).

 2. Carefully remove the integument about the anus and expose the
external sphincter ani muscle (p. 268, and Fig. 113, _i_). Trace it to
its origin. Remove the integument of the scrotum and dissect the
intercolumnar fascia, the levator scroti muscle (p. 271, and Fig. 113,
_j_), the tunica vaginalis communis, and propria (p. 258).

 3. The testis; the epididymis with great care, especially in uncovering
the vasa efferentia; the vas deferens and spermatic cord (p. 259, and
Figs. 110 and 111).

 4. Follow the cord to the external inguinal ring (p. 259) and expose
the ring. Dissect off in order from the inguinal canal: (_a_) The
external oblique muscle; (_b_) the internal oblique muscle; (_c_) the
transversus. In this way the cord is followed with its tunica communis
and tunica propria to the internal inguinal ring.

 5. Trace the vas deferens (p. 260, and Fig. 111) within the abdominal
cavity as far as it can be seen dorsad of the neck of the bladder.

 6. The penis (p. 262, and Figs. 111 and 113). Cut the skin along the
dorsum of the penis and reflect. Dissect the ligamentum suspensorium
penis. Then introduce a bristle into the urethra and remove the
integument from the whole penis and identify the corpora cavernosa and
corpus spongiosum and the urethra.

 7. Remove the fat at the side of the rectum and find the levator ani
muscle (p. 269, and Fig. 162, 11). Transect and reflect it. The internal
sphincter ani (p. 269, and Fig. 113, _h_). Find the external opening of
the anal gland (p. 239); slit and examine it.

 8. Dissect the ischiocavernosus (p. 269) and bulbocavernosus (p. 271)
muscles (Fig. 113), and find the bulbus of the corpus cavernosum beneath
the former. Cut it free from the ischial ramus.

 9. Clean the muscles from the pelvis on the side from which the crus
penis is removed, and remove with bone forceps the body of the pubis and
the ramus of the ischium. Then trace the neck of the bladder to its
junction with the vasa deferentia, and the urethra from that point to
the external opening (Fig. 111). Study the compressor urethræ muscle (p.
271, and Fig. 113, _n_). Find Cowper’s glands (p. 261) and the prostate
gland (Fig. 113). Dissect the other muscles of the urogenital organs
(pp. 268 to 273, and Fig. 113).

10. Slit the urethra on one side throughout its length and find the veru
montanum (p. 261); the openings of the vasa deferentia (p. 261), by
bristles passed into the urethra from them; the openings of the prostate
gland and the openings of Cowper’s glands.

11. Study the structure of the penis (p. 262) by making a cross-section,
and that of the glans by making a longitudinal section. Note, if
possible, the os penis.


C. _Female Urogenital Organs_ (p. 263, and Fig. 112). The kidney and its
ducts and the bladder are like those of the male (p. 255), except the
neck of the bladder, which will be seen in dissecting the uterus and
vagina.

_a._ Without cutting anything examine--

 1. The ovaries (p. 264); the ligaments of the ovary (p. 264, and Fig.
112).

 2. The uterine tube. Its ostium (p. 264).

 3. The body of the uterus (p. 266) as far as exposed.

 4. The cornu of the uterus.

 5. The broad and round ligaments of the uterus (p. 266).

 6. Slit open one Fallopian tube, cornu, and body of the uterus as far
as the junction of the divisions of the body of the uterus.

_b._ Remove the ventral wall of the pelvis on one side only and find the
vagina and urogenital sinus (p. 267). The levator ani muscle (p. 269,
and Fig. 162, 11) must be cut and reflected.

 1. Note the constrictor vestibuli, caudovaginalis, and urethralis
muscles (p. 272, and Fig. 114).

 2. Introduce a probe from the uterus into the vagina and feel with the
finger for the hard cervix uteri (p. 266). Then open the vagina on the
side, but do not cut the os uteri (p. 266).

 3. Examine the cervix uteri and os uteri (p. 266).

 4. Introduce a probe through the neck of the bladder and note its
emergence into the urogenital sinus.

 5. Find the end of the clitoris (p. 267), and its prepuce, and then
dissect the integument carefully from about the external opening of the
urogenital sinus and note an external sphincter of the sinus (M. levator
vulvæ) (p. 272, and Fig. 114), equivalent to the levator scroti in the
male and continuous with the external sphincter ani.

 6. Find (if possible) the corpora cavernosa of the clitoris (p. 267)
and the ischiocavernosi muscles (p. 269).


DISSECTION OF THE CIRCULATORY SYSTEM.


I. THE HEART (p. 274, and Figs. 115-117).

Use the heart from the specimen dissected for the muscles, or from the
specimen on which the viscera were studied.

 1. Study the outside (p. 275, and Figs. 115 and 116), and learn to
recognize all parts. Find the pulmonary veins (p. 275, and Fig. 116,
_g_, _h_, _i_) and cut them, thus separating the heart from the lungs.

 2. The Pericardium (p. 279). In a specimen the thoracic contents of
which have not been injured, dissect the mediastinal septum from the
pericardial sac and remove fat about the great blood-vessels so as to
expose them all fully. Study their relations. Prick and inflate the
pericardium. Slit it lengthwise over the ventricles and reflect it so as
to expose its contents. Study the attachment of serous and fibrous
layers to the heart and their relation to one another.

 3. In dissecting the heart follow the course of the blood, studying
each cavity with the aid of the descriptions (pp. 275-279) as you
proceed. Dissect as follows:

_a._ Remove the dorsal wall of the right auricle (p. 275) and of its
appendage except that part of it to which the venæ cavæ are attached.

_b._ Introduce the probe from the right auricle into the right
ventricle, and feel with the probe the line along which the ventricular
wall joins the septum. Cut along this line so as to turn back the
ventricular wall as a flap, which remains attached at the base of the
ventricle.

_c._ Introduce a probe through the conus arteriosus into the pulmonary
artery and cut along the probe.

_d._ Remove the dorsal wall of the left auricle and its appendage, _but
do not_ remove that part to which the pulmonary veins are attached.

_e._ Make a longitudinal incision beginning at the apex and divaricate
the lips of the cut as you pass toward the base, thus avoiding injury to
the lateral flap of the bicuspid valve. Without injury to the flap or
the columnæ carneæ, remove the heart-wall at the sides of this incision
near the base of the ventricle, as much as necessary to expose the
cavity.

_f._ Pass a probe into the aorta. Introduce scissors behind the septal
flap of the bicuspid valve and slit the aorta without injury to the
bicuspid valve.


II. DISSECTION OF THE BLOOD-VESSELS.

_Preparation and Injection._--A new specimen must be prepared for the
dissection of the blood-vessels. The same specimen may be used, if
necessary, for the dissection of the peripheral nervous system,--one
side being used for the blood-vessels, the other for the nerves,--but it
is much better to use separate specimens for the two systems.

Inject the femoral artery of the specimen with either five per cent.
formalin, or with the mixture of five per cent. formalin and glycerine,
exactly as for the muscles. Then, without removing the canula or
waiting, inject the artery with red starch. This is prepared as follows:

Mix together equal volumes of vermilion (or red lead), glycerine, and
five per cent. formalin. Grind these together in a mortar, so as to
destroy the lumps; strain the resulting mixture through fine muslin.
This color mixture can be preserved in a closed bottle till it is to be
used. Then mix together one volume of dry starch, one and one-fourth
volumes of five per cent. formalin, and one-fourth volume of the color
mixture. See that no lumps are present.

Inject the above red starch mass into the femoral artery. It will drive
into the veins the formalin already injected, and the arteries will be
filled with the red starch.

The veins need not be injected, as they will be found to be filled with
the formalin mixture, colored by the blood, so that they can be traced
without great difficulty.

_Dissection of Blood-vessels._--In general the arteries and veins will
be traced together. It is an excellent plan to make a sketch of each
vessel as it is dissected, showing its origin, branches, and name. This
will be a great aid to the memory and will be of much assistance in
reviewing the vessels. The sketches can later be combined into a
well-ordered drawing. The description of each vessel must of course be
studied as the vessel is dissected.

In tracing blood-vessels _do not_ grasp them between the forceps-blades,
but handle them by taking hold with the forceps of the connective-tissue
coats of the vessels. _Do not_ use the scalpel, but _pull_ away the
connective tissue and fat with fine forceps, using two pairs of forceps
or one forceps and the tracer.

Variations are especially common in the blood-vessels, and the student
must not be surprised to find considerable deviations from the
conditions described and figured in the text. These variations usually
present nothing new in principle and are easily understood by comparing
them with the structures described.

_Directions for Dissecting the Blood-vessels._--Make a median
longitudinal incision through the skin from the symphysis of the jaw to
the caudal end of the xiphoid process. About three or four centimeters
caudad of the cranial end of the sternum make an incision at nearly
right angles to this, passing from the first incision on the ventral
side of the left arm about to the elbow. Reflect the flaps of skin, so
as to uncover the left side of the thorax and the under surface of the
arm, exposing the pectoral muscles. Isolate and transect the pectoral
muscles one at a time, cutting each near its thoracic attachment. (The
muscles (p. 145) should be reviewed at the same time.) In this way the
nerves and blood-vessels of the axilla are exposed (Fig. 122, p. 295).

Find the axillary artery and vein (Fig. 122, _f_ and _g_) emerging from
the thorax just craniad of the first rib, along with the nerves of the
brachial plexus. Remove connective tissue, etc., so that the vessels and
nerves are well isolated as they pass out of the thorax. Take great
pains not to puncture the vessels, particularly the veins.

Then remove the left side of the thorax by cutting through the first rib
near its sternal end and then near its dorsal end, without injury to the
vessels and nerves, cut the other ribs in the same way, and take out the
thoracic wall.

Now find with tracer and forceps the great blood-vessels leaving the
cranial end of the heart (see Fig. 118). Take the greatest pains not to
injure them. Find the aorta and aortic arch (p. 281); the left
subclavian artery (p. 283) (continuous with the axillary); the
innominate artery (p. 282), and the beginnings of its three branches
(see Fig. 115). Find also the superior vena cava, the innominate veins,
and the subclavian vein, continuous with the axillary vein.

I. Study the smaller branches of the thoracic aorta (p. 283, and Fig.
118)--the intercostals, the bronchial and œsophageal arteries, and the
first pair of lumbar arteries. (The coronary arteries will be examined
later.)

II. Dissect the subclavian and its branches (p. 290) as follows:

 1. The internal mammary (p. 292). Follow it onto the ventral wall of
the abdomen. Follow the vein at the same time (p. 318).

 2. The vertebral artery (p. 291). Find its beginning, but do not trace
it at present.

 3. The costocervical axis (p. 292). Find its beginning, and trace the
superior intercostal branch some distance The other branches are not to
be followed at present.

 4. The thyrocervical axis (p. 293). Find its beginning, but do not
trace it at present.

 5. The axillary artery (continuation of the subclavian) (p. 294).
Follow its branches, tracing at the same time the axillary vein (p.
318). (Consult Fig. 122.) In tracing the blood-vessels, separate the
muscles, but do not cut them except where absolutely necessary. (The
muscles should be reviewed as the vessels are traced.)

The following notes may be of assistance in following the different
branches:

(_a_) The anterior thoracic was probably cut in dissecting the pectoral
muscles; it may be found, but its distal end is probably cut off.

(_b_) The long thoracic is easily followed.

(_c_) The subscapular. Follow the main artery before dissecting its
branches. Where the subscapular disappears between the long head of the
triceps, the latissimus dorsi, and the scapula, it may be traced and
found again as follows: Remove the skin from the outer side of the
shoulder,--taking great pains to remove _only_ the skin and not to
injure the vena cephalica (p. 319), a large vein that lies just beneath
the skin on the lateral surface of the shoulder, coming from the elbow.
The branches of the subscapular will be found appearing on the lateral
surface of the arm in the angle between the spinotrapezius, the long
head of the triceps, and the infraspinatus. The distal branches may then
be followed.

(_d_) The posterior circumflex (p. 296) may be traced distad in a
similar manner, by seeking it beneath the caudal border of the
spinotrapezius. (Do not injure the vena cephalica.)

(_e_) The other branches of the brachial artery and vein present no
difficulty till we come to the collateralis radialis superior (Fig. 122,
_x_). This must be traced with great care, along with the vena mediana
cubiti (p. 319, and Fig. 122, _y_). Remove the skin from the extensor
side of the forearm, taking great pains not to remove anything more than
the skin. The artery and vein lie beneath the skin and should be traced
to the hand (see Fig. 130).

Along with the collateral radial artery trace the vena cephalica (p.
319, and Fig. 130, _a_ and _c_). Follow it across the shoulder, noting
the branch to the posterior circumflex vein.

The remainder of the blood-vessels of the arm present no special
difficulty (see Figs. 123 and 124).

Make a diagram of the subclavian artery, as far as dissected.

III. Remove the skin from the sides of the neck, exposing the
sternomastoid muscles and the external jugular veins crossing them (see
Fig. 131). Clean the surface of the sternomastoid muscles, without
injuring the vein; separate the two muscles caudad, and cut each close
to the attachment to the sternum. Find the sternohyoid and sternothyroid
muscles, and cut them close to their attachment to the first rib.
Uncover the right side of the thorax in the same way as the left, cut
the ribs without injury to the nerves and vessels of the right axilla,
cut the internal mammary artery and vein (after tying the latter), and
thus remove the sternum with nearly the entire thoracic wall.

The blood-vessels of the thorax may now be more completely exposed. (If
the nerves are to be dissected on the same specimen, find the phrenic,
vagus, and sympathetic nerves (Fig. 157), and take the greatest pains
not to injure them.)

 1. The coronary arteries and the veins of the heart (pp. 281 and 316).

 2. The superior vena cava (p. 316). Find its branches. Trace the azygos
as far back as the diaphragm without dissecting it at all.

Find the division of the innominate (p. 318) into subclavian and
external jugular.

Trace next--

 3. The external jugular (p. 319). Remove the skin from the side of the
face and trace its branches (Fig. 131). The internal jugular, vena
facialis profunda, the submentalis, and the deep terminal branches of
the posterior facial cannot be followed at this time; veins shown on
Fig. 131 should all be found, however.

 4. Trace the thyrocervical axis and its branches (p. 293). Add them to
your diagram of the subclavian.

 5. Follow the common carotid artery (p. 283) and internal jugular vein
(p. 320). Find the division of the common carotid into its terminal
branches and then dissect its lateral branches and those of the internal
jugular (see Fig. 119).

 6. The external carotid (p. 285, and Fig. 119). Follow its branches
with the exception of the internal maxillary.

 7. The internal maxillary (p. 287). Find its inferior alveolar branch
first and follow it by cutting away with bone-forceps the ventral border
of the lower jaw. To follow its other branches and those of the carotid
plexus, remove the zygomatic arch, cut the temporal, masseter, and
pterygoid muscles, and cut the mandible behind the incisor teeth and
remove it. The branches which pass into the skull are not to be followed
at present. The posterior facial vein (p. 323), the vena facialis
profunda (p. 323), and the submental vein (p. 323) may be followed at
the same time.

 8. The internal carotid (p. 285). Follow it to the point where it
enters the cranium.

 9. Trace the other branches of the costocervical axis (p. 292). To do
this, cut the arteries and nerves of the axilla on the side on which
they have been dissected, allowing the arm to fall backward. Then trace
the branches of the costocervical axis with tracer, scalpel, and
bone-forceps, taking care not to injure the vertebral artery. Add these
branches to your diagram of the subclavian.

10. The vertebral artery (p. 291). Trace it to the foramen
transversarium of the sixth cervical vertebra. Then with bone-forceps
follow it to the atlas and into the atlantal foramen. Add this to your
diagram of the subclavian.

11. The basilar artery (p. 291) and the other arteries of the brain (p.
289) are best studied on a preparation, similar to that shown in Fig.
121. To obtain such a preparation it is only necessary to remove the
brain (for directions, see p. 462) of a specimen in which the arteries
have been injected.

(12. Veins of the brain and dura mater (p. 324). These can be worked out
only with much difficulty, except on specimens injected with gelatine.
The skull must be chipped away and the veins followed without destroying
them.)

13. Trace the pulmonary veins (p. 315) (filled with red injection) and
the pulmonary artery (p. 280).

IV. Vessels in the abdominal cavity.

 1. Open the abdominal cavity; find the superior mesenteric vein (p.
326, and Fig. 132) in the duodenal mesentery near the border of the
pancreas. Inject this in both directions with white starch and then
dissect the portal vein and its tributaries without injuring any of the
structures in the abdomen (p. 326, and Fig. 132).

 2. Follow the inferior vena cava (p. 325) from the heart to the
diaphragm and then follow it to its tributaries in the abdominal cavity.

 3. Dissect the branches of the abdominal aorta (p. 301) and of the
inferior vena cava (Fig. 126). Make diagrams of the vessels dissected
and review as far as necessary the viscera concerned.

V. The external iliac and its branches (vessels of the hind limbs) (pp.
309 and 329, and Figs. 127, 128, and 163).

Follow the branches of the external iliac arteries and the corresponding
veins in the same manner as the vessels of the arm were traced, cutting
the muscles only so far as absolutely necessary. Make diagrams of the
vessels dissected.

Make a diagram (_a_) of the arterial system as a whole; (_b_) of the
venous system as a whole.


THE LYMPHATIC SYSTEM (p. 330).

It will hardly be found practicable to have each student make a
dissection of the lymphatic system, and such parts of it as are to be
studied may best be shown on a specimen prepared for demonstration
purposes.

The thoracic duct and the receptaculum chyli may be demonstrated by the
following well-known method: A lean cat is fed with milk about two hours
before killing it. An egg may be beaten up with the milk to advantage.
Kill the cat with chloroform, and inject the arteries with colored
starch through the femoral, in the usual way. The thoracic duct, the
receptaculum chyli, and the lymphatics leading to the receptaculum chyli
will be colored white by the milk, and can therefore be easily followed.
For this purpose the abdomen should be opened, and the left side of the
thorax removed, as in the dissection of the blood-vessels. The thoracic
duct will be found at the left side of the aorta and may then be traced
in both directions.

For a more complete study of the lymphatics they should be injected.
This is done as follows: Make a glass canula with a small point, and
leave the point sharp. Connect this to the syringe by means of a rubber
tube. Use a saturated solution of soluble Prussian blue as injecting
fluid. Employ a freshly killed animal.

For injecting the lymphatics of the limbs, make with some pointed
instrument, as the tracer, a small hole in one of the pads on the sole
of the foot. Introduce the point of the canula into this opening and
inject the fluid. This will pass into the spaces in the connective
tissue of the pad, which will swell up, and the colored fluid will pass
from the connective-tissue spaces into the lymphatics. Pressure must be
maintained with the syringe for a considerable time,--fifteen minutes to
a half-hour for a good injection of the main trunks of the lymphatics of
the limbs. The movement of the fluid should be facilitated by pressing
and manipulating the limb at the same time with the hand,--in such a way
as will tend to drive the fluid proximad.

The lymphatics of the head may be injected in a similar manner, the
canula being introduced into the upper and lower lip, or into the bare
surface at the end of the nose.

The internal lymphatic vessels may be injected by injecting the
lymphatic glands with which they are connected. This may conveniently be
done as follows: Draw out to a fine point the tip of an ordinary pipette
or medicine-dropper. The point should be fine, but should taper rapidly
in a conical fashion, so that when the point is inserted the part of the
glass tube behind it will close up the opening.

Fill the pipette with soluble Prussian blue; insert the point into the
gland, and inject the fluid slowly. The lymphatic vessels passing from
the glands will be filled. By injecting thus the large lymphatic gland
(“pancreas Aselli”) in the mesentery, the abdominal lymphatics, the
receptaculum chyli, and the thoracic duct may be injected.

By using thin gelatine colored with Prussian blue as an injecting fluid
permanent preparations may be obtained; of course the process of
injection is then less simple, and should be looked up in some manual of
methods.


NERVOUS SYSTEM.


I. THE SPINAL CORD (p. 335).

Use the specimen on which the muscles were dissected. (Or if the
peripheral nerves are not to be dissected on the specimen used for the
blood-vessels, that may be employed.)

Make a longitudinal dorsal median incision of the skin, between the back
of the head and root of the tail. Reflect the skin for one or two inches
on each side of the incision and cut away the muscles covering the
neural arches of the vertebræ from the third cervical to the seventh or
eighth thoracic inclusive.

Remove with bone-forceps the neural arch of one of the last cervical
vertebræ and find the spinal nerve emerging from the intervertebral
foramen. Isolate the nerve for a short distance, then proceed craniad,
removing the neural arches on one side and isolating the nerves until
the third has been uncovered. The ganglion of the second nerve should be
sought among the muscles on the dorsal surface between the atlas and
axis, and after it has been isolated the arch of the axis may be
removed. (The nerve may be found beneath the clavotrapezius and traced
to the ganglion.)

The ganglion of the second nerve should be isolated in or near the
atlantal foramen, the muscles to which it passes turned aside, and the
arch of the atlas removed. Having thus uncovered the first two or more
spinal ganglia, proceed caudad, removing the vertebral arches, until the
whole cord and its nerves are exposed. Then--

 1. Study the cord, enlargements, filum terminale, etc. (p. 334, and
Figs. 133 and 136).

 2. Slit open and reflect the dura mater (p. 337) for an inch or two.

 3. Demonstrate the arachnoid by pulling it off with forceps.

 4. Reflect the pia mater in the same way as the dura mater.

 5. Study the fissures and grooves of the cord.

 6. Cut across the cord with fine scissors at the point where it is
freed from its membranes and examine the section. Note the arrangement
of gray and white matter and the fissures and grooves, particularly the
anterior or ventral. Demonstrate the central canal with the blowpipe.

 7. Study the origin of the spinal nerves (p. 337). Count them.
Direction of exit? Carefully clean one in the thoracic region from dura
mater and connective tissue, with fine scissors, and study dorsal and
ventral roots and ganglion (see Fig. 135). Then follow it out and find
its dorsal ramus and ventral ramus and the communicating branch of the
latter with the sympathetic system. Do not trace the peripheral branches
of the nerve at present.


II. THE BRAIN (p. 339).

The brain will usually be found to be in an entirely satisfactory
condition for study in any specimen injected with five per cent.
formalin or the glycerine and formalin mixture. The brain is a little
swollen, but all parts are well preserved, and the white and gray matter
are clearly marked off from each other. Either the specimen used for the
muscles or that employed for the blood-vessels may therefore be
used,--or if the brain was removed from the specimen employed for the
viscera, that will be satisfactory.

The following directions for removing the brain are designed for
specimens preserved as above. For removing the _fresh_ brain the process
is essentially similar, but as the brain is then very soft, care should
be taken not to tear it. The fresh brain should be preserved in the
alcohol-formalin mixture given below, and should be allowed to rest only
on some soft substance, as absorbent cotton.

Remove the head from the body by cutting through the neck a little
craniad of the first rib if this has not already been done. Remove all
skin, muscles, and other soft parts from the head and cervical vertebræ,
as far as possible. Remove the structures in the orbit by cutting
through the zygomatic arch at each end, and removing it. The lower jaw
should also be removed, if this has not already been done. (If a fresh
specimen is used, and the head is to be employed for other purposes, the
brain can be removed without separating the head from the body, and
without taking away the lower jaw and other structures on the ventral
surface of the skull.)

Have at hand dissecting-instruments and a dish containing alcohol and
formalin in the following proportions (Parker and Floyd’s mixture):

  95 per cent. alcohol     6 parts
   2 per cent. formalin    2 parts

In the bottom of the dish should be placed a little absorbent cotton, to
support the brain.

In removing the brain have at hand entire and dissected skulls and note
the relations of parts on these as far as necessary before cutting the
specimen.

With bone-forceps make a small opening in the parietal bone so as to
expose the dura mater, but do not cut through the dura mater. With some
blunt instrument free the dura mater from the bone about the opening,
and continue to cut away the bone until the dorsal and lateral faces of
the cerebrum are fully exposed craniad of the tentorium. The olfactory
bulbs (Fig. 137, _I_) should be exposed carefully and as fully as
possible. Cut away the dorsal arch of the atlas and carefully insert the
forceps in the foramen magnum and, working as before, remove the
squamous portion of the occipital and the parietal bones as far as the
tentorium and as far ventrad as possible. Leave the dura mater intact if
possible. Free the surface of the tentorium from the dura mater,
carefully separate slightly the cerebellum and cerebrum; insert the
bone-forceps (not too far) with the blades inclined from without
ventromediad, and cut the tentorium on each side. Remove it slowly,
cutting adhesions to the dura mater. That part of the dura mater which
dips between the cerebral hemispheres is the falx cerebri. Cut the dura
mater along both sides of the falx cerebri and remove it by turning it
down at the sides and cutting it at the level of the cut edge of the
bone. Remove it also from the cerebellum and notice how it dips down on
both sides of the tentorium and in close contact with it. Cut the falx
at the cranial end between the olfactory bulbs and cut the tentorial
dura (cut its adhesions, but do not remove with it the pineal body). The
falx and tentorial dura may then be removed.

Allow the head to hang sideways over the dish of alcohol-formalin in
such a way that the brain will tend to fall out of the cranium. Free the
olfactory bulbs from the bone. Then begin at the caudal end and tilt the
brain out with the handle of a scalpel. In doing this note carefully and
cut the cranial nerves. They should be left with central ends as long as
possible, and those on the side which is uppermost should be cut first.
In doing this refer to the foramina in the base of the skull and to Fig.
138. Take especial pains also not to break off the hypophysis, which is
lodged in the sella turcica.

The brain falls out and rests with its dorsal surface on the cotton. Now
remove the remainder of the dura mater, carefully cutting all adhesions
to nerves. Remove also the pia mater, as far as that can be done without
pulling off at the same time parts of the brain-substance. Preserve the
brain in the alcohol-formalin mixture.

_Study of the Brain._--In the study of the brain demonstration specimens
are to be used as much as or more than your own specimen. See everything
on a demonstration preparation before attempting to expose it in your
own specimen.

I. Examine the brain of a shark or of a frog. Cranial nerves may be
neglected, but the divisions of the brain should be recognized in dorsal
and ventral views and in longitudinal sections, and sketched.

II. Read the general description of the cat’s brain (pp. 339-343), using
your own specimen and a longitudinal section. Cut nothing on your own
specimen except when especially directed to do so. Study the cavities on
a preparation. Compare the diagrams (Figs. 139 and 140) and the figures
of the brain.

III. Study the individual parts as follows. To avoid errors make
constant reference to preparations and figures.

 1. The medulla (p. 344 and Figs. 138 and 141). Use your own specimen
and a preparation and dissect out carefully the cranial nerves on your
own specimen.

 2. The cerebellum (p. 347). Study it entire, then to expose the fourth
ventricle (p. 349) slice away with a very sharp scalpel one-half of the
cerebellum by making a median longitudinal incision and then horizontal
incisions.

 3. The pons (p. 347).

 4. The mesencephalon (p. 351, and Figs. 141 and 142). Study it first in
a preparation. Then study the floor on your own specimen; origin of
third nerves.

 5. The diencephalon (Figs. 141 and 142). Study the roof and thalami and
the pineal body on a preparation and on a longitudinal section; the
floor on your specimen.

 6. The telencephalon (p. 357). (Note that only _one_ side of this is to
be dissected.)

_a._ Study it externally; sulci and gyri (Figs. 145 and 146).

_b._ Examine a preparation showing the corpus callosum (Fig. 147). Then
slice away with a very sharp scalpel the top of _one_ hemisphere nearly
to the corpus callosum (see the preparation). Expose the corpus callosum
on this side to its cranial and caudal borders, by _tearing_ away the
brain-substance at its side and above it.

_c._ Raise the corpus callosum at the side and remove it, thus exposing
the lateral ventricle in which note the septum pellucidum and fornix,
the corpus striatum, and choroid plexus of the lateral ventricle (Fig.
148). (These are to be exposed on _one_ side only, the other being left
intact.)

_d._ Expose the anterior and inferior horns of the ventricle and find
the hippocampus, the fimbria, caudal part of the fornix, the foramen of
Monroe, the anterior commissure. See all these also on a preparation
(Fig. 148).

_e._ Remove the occipital and parietal portions of the cerebrum, on the
side already dissected, so as to expose the roof of the third ventricle
and the midbrain in your specimen, and note the pineal body, choroid
plexus of third ventricle, and structures on the roof of the midbrain
(Fig. 141).

_f._ Remove the choroid plexus or roof of the third ventricle and study
again the thalami (Fig. 141).

_g._ Make a longitudinal section of the brain, in the following manner:
Use a very sharp large scalpel, or a razor. Have this wet with the
alcohol mixture at the time of using. Place the brain ventral surface
down on a sheet of cork or a block of soft wood, the long axis of the
brain coinciding with the direction of grain of the wood. Holding the
brain firmly with one hand, place the wet knife between the hemispheres
with its edge resting on the corpus callosum. See that it is in the
median plane and parallel with the long axis of the brain. See also that
it is not inclined to one side or the other, so that it will make on
cutting a median section throughout. The point of the knife should just
reach the cork or wood between the olfactory bulbs. Now draw the knife
caudad, keeping its point against the cork: the brain will thus be
divided.

If the section is not exactly median, observe the amount of divergence
by placing the two halves together and finding the median ventral line.
Then on the half that has _too much_ slice away thin shavings until the
cavities are exposed, showing the section to be median. Compare with a
demonstration section or Fig. 143. Draw the section and compare with a
section of shark’s brain (see Fig. 143).

_h._ Study a series of transverse sections, identifying parts. Observe
especially in these sections the fornix, corpus callosum, and
ventricles, and the distribution of white and gray matter (see Figs.
149-153).


III. PERIPHERAL NERVOUS SYSTEM.

(There are some advantages in dissecting the eye with its muscles before
dissecting the nerves, as a knowledge of the eye-muscles is presupposed
for dissecting some of the cranial nerves. For directions on the eye,
see p. 469.)

A new specimen should be used, if possible, for the peripheral nervous
system, though that used for the blood-vessels can be employed, at
considerable disadvantage.

Prepare as for the blood-vessels. The arteries should be injected with
red starch, to aid in tracing the nerves.


 1. THE CRANIAL NERVES (p. 369) AND SYMPATHETIC SYSTEM (p. 404).

 1. Reflect the skin covering the sternomastoid muscle, and make a
longitudinal incision of the muscle so as to expose the carotid artery.
Lying along the artery find the combined trunk of the sympathetic and
vagus nerves. Follow the vagus (p. 378) first craniad; transect the
muscles as necessity arises, and find its ganglion nodosum and at the
same time locate the superior cervical ganglion of the sympathetic nerve
(p. 404, and Fig. 156). Then find the hypoglossal nerve (Fig. 156, _b_),
passing outside of the carotid artery to the tongue, and the accessory
(Fig. 156, _c_), passing to the trapezius. Cut and reflect the digastric
muscle and find the small glossopharyngeal nerve (Fig. 156, _a_),
passing to the surface of the bulla and then beneath the carotid artery.

 2. Follow the vagus (p. 378) caudad to its termination. To do this it
is necessary to remove one side of the thorax, as in dissecting the
blood-vessels. Do not injure the nerves of the axilla, nor the phrenic
or sympathetic nerves. For the vagus in the thorax, compare Fig. 157.
Find the branches of the nerve; in dissecting them, pull on them to make
them tense. They are then more easily visible. To dissect the abdominal
portion of the vagus, open the abdominal cavity, and compare Fig. 164
(p. 407).

 3. Dissect the sympathetic (p. 404), following it and its branches to
the pelvic region (Figs. 156, 157, and 164).

 4. The hypoglossal (p. 383, and Fig. 156, _b_).

 5. The glossopharyngeal (p. 378, and Fig. 156, _a_).

 6. The accessory nerve (p. 382, and Fig. 156, _c_; Fig. 158, 1).

Cut away a portion of the tympanic bulla and the base of the skull,
sufficient to follow these nerves in the jugular foramen, to the brain.

 7. Locate the stylomastoid foramen and pick away overlying tissue until
the facial nerve is found emerging and then follow its branches to their
distribution (p. 375, and Fig. 155).

 8. Expose the ventral surface of the pterygoid muscles just mediad of
the angle of the jaw. Divide and reflect them, and the mandibular
division of the fifth nerve (p. 373, and Fig. 154) will be found dorsad
of them and of the internal maxillary artery. The chorda tympani (p.
375) passes ventrad of the artery to join the lingual. Follow out (1)
the lingual branch (p. 375) (with the chorda tympani), and (2) the
inferior alveolar (p. 375) by cutting away the ventral border of the
mandible. Then cut the mandible near the canine tooth, and pull it to
one side, and follow out the muscular branches of the mandibular nerve.

 9. Remove the mandible and find the maxillary nerve (p. 371) emerging
from the foramen rotundum. Follow its branches and find the
sphenopalatine ganglion (p. 372).

10. Remove the zygoma so as to expose the whole ventral aspect of the
orbit. Carefully pick away the fat in the orbit without injuring any
nerves, so as to expose the four recti muscles and the inferior oblique
(see p. 411, and Fig. 166). Find the abducens nerve (p. 375, and Fig.
154), entering the dorsal edge of the lateral rectus, and follow it
back. Look on the inner surface of the inferior rectus for the branch of
the third nerve (p. 369) which supplies it. Find the branch of this
nerve which runs to the inferior oblique muscle, and on it the ciliary
ganglion; find the branches to the ciliary ganglion from the ophthalmic
nerve and follow them (p. 371). Follow also the short ciliary nerves (p.
370) to the eyeball.

11. Trace the third nerve (p. 369) to its foramen of exit and find its
branches. Where it passes between the superior and lateral recti, find
the ophthalmic nerve (p. 370) by its side and trace its branches.

12. Find the fourth nerve (p. 370), passing outside of the lateral
rectus at its origin and entering the superior oblique.

13. Follow the third, fourth, fifth, and sixth nerves into the skull by
chipping away the bone and removing the dura. Note the semilunar or
Gasserian ganglion (p. 370, and Fig. 138, _k_) and the origin of the
fifth nerves from it, and the relation of the ventral root of the fifth
nerve to the mandibular nerve.


 2. SPINAL NERVES.

The spinal nerves may be dissected on the same side used for dissecting
the cranial nerves. (If an undissected specimen is used, remove the skin
from the side of the neck, and cut the sternomastoid, sternohyoid, and
sternothyroid muscles, as directed for the vagus and sympathetic.)

_Cervical Nerves_ (p. 383).--The ventral rami of the cervical nerves are
to be sought as they pass out between the bundles of the scalenus, or
between the scalenus and longus capitis, in the neck. This region has
already been uncovered in dissecting the vagus and sympathetic (Fig.
156). Dissect first the _second_ cervical (p. 385). Find its ventral
ramus as it emerges between the levator scapulæ ventralis and
cleidomastoid (Fig. 158, 2), and follow its branches,--the auricularis
magnus (5) and cutaneus colli (6). Find its _dorsal_ ramus, the great
occipital nerve (p. 384), by reflecting the clavotrapezius muscle; the
nerve will be found emerging from the underlying muscles close to the
craniomedial angle of the clavotrapezius, near its origin. Trace the
nerve in both directions.

The ventral ramus of the first cervical (p. 385) will be found emerging
from beneath the wing of the atlas, a little distance craniad of the
second (Fig. 156, _j_). Trace it. To find its short dorsal ramus, the
suboccipital nerve (p. 384), it is necessary to dissect apart the
muscles on the dorsal side of the atlas till the nerve is found passing
from the atlantal foramen.

Dissect the third, fourth, and fifth nerves (p. 385, and Fig. 158).

_Brachial Plexus_ (p. 386, and Figs. 159 and 160).--The brachial plexus
has been partly uncovered in dissecting the vagus and sympathetic. (If a
new specimen or the opposite side is used, reflect the skin from the
ventral surface of the thorax and arm, and cut the pectoral muscles,
thus uncovering the vessels and nerves of the axilla.) Reflect the skin
from the ventral surface of the upper arm. (Do not use scalpel, but tear
the skin from the muscles. In this way the nerves will be seen passing
to the skin, while if the scalpel were used the nerves might be cut.)

Tie the axillary vein or its two branches in two places, and cut the
vein between the tied regions. Leave the arteries as guides for
dissection, but remove the veins. Now clean thoroughly the nerves
forming the brachial plexus as they pass from the thorax or neck. Be
careful not to injure any of the fine nerves or the interconnections of
the nerves in doing this. Find and distinguish clearly the fifth, sixth,
seventh, and eighth cervical nerves and the first thoracic, as they
emerge from the neck or thorax. (Compare Fig. 159 and Fig. 157,
_V_-_VIII_ and _I′_.)

Follow out the branches of the plexus, noting the origin and
distribution of each branch, in order to determine its name. To follow
the phrenic (p. 388, and Fig. 157, _f_), remove a portion of the
thoracic wall. In following the other branches of the plexus, pull back
the skin wherever an exposure is to be made, and separate the muscles.
The epitrochlearis may be cut near the elbow, and the clavobrachial near
the shoulder. In following the interosseous branches of the median nerve
the fifth head of the flexor profundus, and the extensor brevis
pollicis, may be cut. As a rule it will not be necessary to cut other
muscles.

_Thoracic and Lumbar Nerves._--One or two of the thoracic nerves (p.
393) should be dissected from the outside by finding the intercostal
nerve along the caudal border of one of the ribs and tracing it in both
directions. The nerve may be exposed by removing the external muscles
covering the rib, and cutting the external intercostal muscles. The
dorsal ramus should be traced after the ventral ramus has been studied.

The first lumbar nerve (p. 395) should be dissected in the same way.

The other lumbar and sacral nerves (pp. 395-400) are best dissected from
within.

The alimentary canal and its appendages should be removed from the
abdomen, leaving only five or six centimeters of the caudal end of the
rectum. The kidneys and urogenital organs may be left, to be removed
during dissection. (Compare Fig. 162.)

Turn one of the kidneys to the other side, and find the second lumbar
nerve (Fig. 162, _a_) appearing at the lateral border of the iliopsoas
muscle. Trace it to its origin; trace it also distad, following both
branches. It will be necessary to trace the nerves through the abdominal
wall, then find them from the outside, and follow them to their
distribution.

The third nerve (Fig. 163, _b_) may be found by dissecting apart the
fibre-bundles of the iliopsoas and psoas minor, and following in the
same way. The kidneys, ureters, vena cava, and aorta may be removed as
occasion arises.

The remainder of the lumbar nerves may be found in order, in a similar
manner. Follow the saphenous nerve and its branches (p. 397) by removing
the integument from the medial side of the leg (see Fig. 127, p. 310).
To dissect the sacral nerves (p. 399) separate the innominate bones at
the pubic symphysis and divaricate them. Find the nerves arising from
the sacral plexus, by cutting the levator ani muscle. After N.
hemorrhoidalis inferior and N. pudendus have been traced, the rectum and
urogenital organs may be removed, taking great care not to remove more
than is necessary. To dissect the great sciatic nerve (p. 400, and Fig.
163), separate the biceps and caudofemoralis near their proximal ends
and find the large nerve-trunk (_a_). Then lift the biceps away from the
nerve, cut that muscle near its middle, and reflect it. The nerve may
now be followed to its terminal branches; during the process cut the
muscles only when absolutely necessary. The inferior gluteal nerve (_i_)
will be found on the dorsal surface of the great sciatic; by cutting the
caudofemoralis and gluteus maximus muscles near their insertions and
turning them back the distribution of the nerve may be followed. The
superior gluteal (_j_) will be found at the cranial margin of the
pyriformis by reflecting the gluteus medius in the same way; the tensor
fasciæ latæ may also be cut.


SENSE-ORGANS.


I. THE EYE (p. 410).

Use any specimen on which one side of the head has been left intact.
Remove the head from the body by cutting through the neck a little
craniad of the first rib.

Study the eye externally. Observe the eyelids, the conjunctiva,
nictitating membrane with its cartilage, and the Harderian gland (Fig.
165); the two openings of the lachrymal duct, the Meibomian glands if
possible.

Remove the zygomatic arch and expose the orbit and the structures which
it contains. Study the periorbita (p. 409), and find the lachrymal gland
(p. 410).

Study the muscles of the eyeball (p. 411, and Fig. 166). The lateral
rectus on the lateral surface will perhaps be first found, and its
tendon traced beneath the inferior oblique. Use great care not to injure
the levator palpebræ superioris.

After studying the muscles, find the optic nerve. Cut it and the
muscles, and remove the eyeball for farther study.

_The Eyeball_ (p. 412, and Fig. 167).--For an examination of the eye it
is well to have a fresh specimen and one hardened in formalin or
alcohol. The hardened specimen is more essential, however. An eye from
one of the specimens used in dissection is usually satisfactory. All
accessory portions should be trimmed from the eyeball, leaving only the
spherical ball with a short stalk formed by the optic nerve.

Observe such features of the eye as can be seen externally: the optic
nerves, sclerotic, cornea, iris, and pupil. This should be done on a
fresh specimen, if one is at hand. The changes in size and form of the
pupil can be observed in the living cat by changing it from a light to a
dark place and _vice versa_.

_Dissection._--Examine the internal structures on a preparation. Then
with fine scissors and forceps remove from the eye about one-fourth of
the wall, in the form of a quadrant having one point at the optic nerve,
the other at the centre of the cornea. The coats of the eye can then be
studied on the piece removed, while the other structures will be visible
within the eyeball. No special directions are necessary for observation
of the structures described, unless it be the capsule of the lens and
the zonula ciliaris. The capsule of the lens may be demonstrated by
tearing a bit of it off with fine forceps. The zonula ciliaris is easily
seen by divaricating the edges of the cut made in removing the quadrant,
so as to stretch the fine fibres of which the zonula is formed.


II. THE EAR (p. 415).

(The muscles of the external ear are of little practical importance, and
will doubtless usually be omitted.)

(1) The External Ear. Read the description of the external ear (p. 415),
verifying it by examination and comparison of an ear still covered with
integument, in the natural condition, and of a preparation of the
isolated cartilages of the ear (Fig. 168). The latter may be obtained by
dissecting the skin and muscles from a fresh ear.

(2) The scutiform cartilage (p. 418) should be observed in the natural
position, and as isolated.

(3) The muscles of the external ear (p. 418, and Fig. 169). Those
connecting the external ear with other parts of the head have been
studied in connection with the facial muscles. The remainder will be
studied on an external ear removed according to the directions given on
page 435.

Remove the integument from the convex surface of the auricle,
sufficiently to expose the entire extent of the muscles.

 1. The rotator auris. Transect.

 2. The adductor auris superior (Fig. 169, 1).

 3. The adductor auris medius (2).

 4. The transversus auriculæ (Fig. 63, _i_, p. 97).

 5. The auricularis externus (Fig. 169, 10).

 6. The helicis (Fig. 169, 3). To expose this it will be necessary to
remove the integument from along the cranial border of the inner surface
of the auricle.

 7. The antitragicus (Fig. 169, 6). Remove the integument farther if
necessary.

 8. The tragicus medialis (Fig. 169, 5, 5′).

 9. The conchæus externus (Fig. 169, 9).

(4) Remove the tympanic bulla and petrous bone from the rest of the
skull, by the use of bone-forceps and scalpel. Trim away all soft tissue
(including the cartilaginous auditory meatus), and all other bony parts
from these, but leave them uninjured.

(5) Find the Eustachian tube and study it (p. 423).

(6) Study specimens of the bones of the middle ear (p. 423, and Figs.
171 and 172).

(7) The middle ear should be studied on a demonstration preparation,
then dissected as follows:

Remove with bone-forceps the medial side of the tympanic bulla (the
entotympanic). Note the two cavities within the bulla, with the shelf
separating them. Observe the fenestra cochleæ. Now remove with the
forceps the shelf, first breaking through the middle part, then removing
the rest with care. Remove part also of the membranous lining of the
cavity, till the inner surface of the tympanic membrane, with the
malleus crossing it, is visible. Observe the tensor tympani muscle (p.
424) attached to the malleus by its small tendon. Next, with
bone-forceps, fracture the thick, bony portion uniting the caudal end of
the petrous with the caudal part of the ring of bone surrounding the
external auditory meatus. These two parts may then be separated with the
fingers, leaving the petrous bone on one side, the meatus, tympanum, and
malleus on the other (Fig. 170). The head of the malleus may then be
observed, with the incus attached to it. Note also the stapes, in the
fenestra vestibuli, with the stapedius muscle (p. 424) attached to it.

(8) The internal ear (p. 424). Note the fenestra vestibuli and fenestra
cochleæ and the promontory (p. 34). Study the cochlea and vestibule on a
demonstration preparation and compare with Fig. 173. Then remove the
wall of the promontory and find the cochlea. Open the vestibule and find
as many of the openings of the semicircular canals as possible. Study
the semicircular canals on demonstration preparations, consulting Fig.
173. The semicircular canals may, if desired, be exposed on your own
specimen, by cutting away the surface of the bone in places indicated in
the description (p. 426), and inserting fine bristles (those from the
sensory hairs on the face of the cat are excellent for this purpose).

The membranous labyrinth (Fig. 173) may be isolated by decalcifying the
petrous bone with ten per cent. nitric acid, then dissecting out the
labyrinth. This is an operation of considerable delicacy, but at least
one or two specimens for demonstration should, if possible, be prepared
thus and kept in the laboratory.



INDEX.


  Abdominal aorta, 301
    arteries, 301
    cavity, 217, 218
    muscles, 153
      dissection, 441
    veins, 326
  Abducens nerve, 347, 375
  Abductor auris brevis, M., 100, 435; longus, M., 100, 435
    brevis pollicis, M., 184, 439
    caudæ (coccygis) externus, M., 137, 447; internus, M., 137, 446
    cruris, M., 195
    digiti quinti, M., 185, 439; secundi, M., 185
    medius digiti quinti, M., 215
  Accelerator urinæ, M., 271
  Accessory nerve, 346, 382
    process, 6, 8
  Acetabular bone, 76, 78
    notch, 79
  Acetabulum, 76, 78, 87
  Achilles, tendon of, 204, 206
  Acromiodeltoid muscle, 157, 438
  Acromion process, 62, 64
  Acromiotrapezius, M., 116, 436
  Adductor auris inferior, M., 104, 435; medius, M., 419, 470; superior,
    M., 419, 470
    digiti secundi, M., 185
    femoris, M., 198, 444
    longus, M., 199, 444
    medius digiti quinti, M., 215
    pollicis, M., 185, 439
  Aditus laryngis, 246
  Adrenolumbar arteries, 304
    veins, 326
  Alæ magnæ, 26, 27
    parvæ, 29
  Albuginea, 260
  Alcohol as preservative, 431
  Alcohol-formalin for brains, 463
  Alimentary canal, 221; dissection of, 449
  Alisphenoids, 25, 27
  Alveolar border, 39, 47
    nerve, inferior, 374, 375
    process, 39
  Alveoli, 48
  Ampulla (ear), 426
    of Vater, 236
  Anal glands or sacs, 239; constrictors of, 269
  Anapophysis, 6
  Anastomotica magna, A., 297
  Anconeus, M., 170, 438
  Anconeus internus, M., 170
    lateralis, M., 167
    longus, M., 168
    posterior, M., 168
  Angle of rib, 18
  Angular process, 19, 48
    vein, 321
  Ankle, bones of, 82
    ligaments of, 91
  Annularis, 72
  Annular ligaments, 75, 173, 213
  Ansæ, 386
  Anterior cerebral artery, 289
    circumflex artery, 296
    commissure, 357, 365
    facial vein, 321
    fossa, 59
    perforated substance, 362
    spinal artery, 291
    superior process, 78
    Sylvian gyrus, 359
    sulcus, 359
    thoracic artery, 294; nerves, 387
    tibial artery, 313
    transverse processes, 11
  Antibrachial fascia, 172
  Antibrachium, muscles of, 172
  Anticlinal vertebra, 6
  Antihelix, 416
  Antitragicus, M., 421, 470
  Antitragus, 417
  Anus, 239
    muscles of, 268
  Aorta, 275, 279, 281, 301
    abdominalis, 301
  Aortic plexus, 408
    semilunar valves, 279
    sinus, 279
  Apparatus digestorius, 221
    respiratorius, 243
    urogenitalis, 255
  Appendicular fossa, 35, 58
    lobe, 348
  Appendix, 429
  Aqueduct of Sylvius, 342, 343, 350, 351, 352
  Aqueductus cerebri, 342, 343, 350, 351, 352; Fallopii, 35
  Aqueous humor, 414
  Arachnoid, 337, 369
  Arbor vitæ, 349
  Arch, bicipital, 166
    supraorbital, 37, 51
    zygomatic, 47, 49, 52
  Area elliptica, 345
    ovalis, 345
    perforata posterior, 352
  Arm, arteries of, 294
    articulations of, 73
    bones of, 64
    muscles of, 156
      dissection of, 436
    nerves of, 388
    veins of, 318
  Arteria adrenolumbalis, 304
    alveolaris inferior, 288
    anastomotica magna, 297
    anonyma, 282
    articularis genu suprema, 311
    auricularis anterior, 287; posterior, 287
    axillaris, 294
    basilaris, 291, 292
    brachialis, 296
    bronchiales, 283
    carotis communis, 282, 283; externa, 285; interna, 285
    cerebelli anterior, 292; inferior posterior, 292
    cerebri anterior, 289; media, 289;
    posterior, 292
    cervicalis ascendens, 293; profunda, 293
    circumflexa femoris lateralis, 311; humeri anterior, 296; humeri
      posterior, 296; scapulæ, 294
    cœliaca, 301
    colica dextra, 304; media, 303; sinistra, 306
    collateralis radialis superior, 297; ulnaris, 297
    coronariæ, 275, 279, 281
    digitales dorsales, 297; plantares, 314
    dorsalis penis, 308
    epigastrica inferior, 309
    femoralis, 307, 310
    gastrica sinistra, 303
    gastroduodenalis, 302
    gastroepiploica dextra, 303
    genu posteriores, 313
    glutea inferior, 308; superior, 308
    hemorrhoidalis media, 308; superior, 306
    hepatica, 302
    hypogastrica, 307
    ileocolica, 304
    iliaca externa, 307, 309; interna, 307
    iliolumbalis, 306
    infraorbitalis, 290
    intercostales, 283
    intercostalis suprema, 293
    interosseæ, 298, 300
    lienalis, 303
    lingualis, 285, 286
    lumbales, 283, 306
    lumboabdominalis, 304
    mammaria interna, 292
    maxillaris externa, 285, 286; interna, 287
    mesenterica inferior, 306; superior, 303
    meningea media, 289
    metatarsea, 315
    occipitalis, 285
    œsophageæ, 283
    ophthalmica, 289
    palatina descendens, 290; minor, 290
    pancreaticoduodenalis inferior, 303; superior, 303
    phrenica, 304
    poplitea, 311, 312
    princeps pollicis et indicis, 300
    profunda brachii, 296; femoris, 309
    pulmonalis, 275, 278, 280
    pylorica, 302
    radialis, 297; recurrens, 298
    renalis, 304
    sacralis lateralis, 309; media, 301, 309
    saphena, 311
    spermatica externa, 309; interna, 304
    sphenopalatina, 290
    spinalis anterior, 291
    subclavia, 282, 283, 290
    subscapularis, 294
    superior profunda, 296
    suprascapularis, 293
    suralis, 313
    tarsea medialis, 315
    temporalis superficialis, 287
    thoracica anterior, 294; longa, 294
    thoracicodorsalis, 296
    thyreoidea ima, 283, 284; superior, 284
    tibialis anterior, 313; posterior, 313; recurrens, 314
    transversa colli, 293; scapulæ, 293
    ulnaris, 300; recurrens, 298
    umbilicalis, 307
    uterina, 308
    ventriculi dorsalis, 303
    vertebralis, 291
  Arteries (see Arteria), 280
    abdomen, 301
    arm, 294
    bladder, 307
    brain, 289, 291
    foot, 312, 314
    hand, 300
    kidneys, 304
    intestine, 304
    limbs, 294, 309
    liver, 302
    stomach, 303
  Artery (see Arteria)
    cystic, 302
    labial, 286
    mediastinal, 282
    ovarian, 306
    submental, 286
    superior laryngeal, 285
  Articular artery, superior, 311
    circumference, 67
    facet, 4
    processes, 6, 8
  Articulation, atlanto-occipital, 17
    intervertebral, 16
  Articulations of arm, 73
    hind limb, 86
    mandible, 61
  Arytenoid cartilages, 248
  Arytenoideus transversus, M., 250
  Astragalus, 82
  Atlantal foramen, 14
  Atlanto-occipital articulation, 17
  Atlas, 14
  Atrium dextrum, 275
    sinistrum, 279
  Attollens auris. M., 100
  Auditory bulla, 32
    meatus, external, 32, 33, 52, 55, 415, 416; internal, 35, 58
    nerve, 347, 377
    organ, 415
  Auricle (ear), 415
  Auricles of heart, 274, 275, 279
  Auricula, 415
  Auricular appendage, 275, 279
    arteries, 287
    cartilage, 415, 416
    facet, 10
    impression, 77
  Auricularis anterior, M., 104, 419
    externus, M., 420, 470
    posterior, M., 99
    superior, M., 100, 435
  Auricular nerve, 379; great, 385; posterior, 377
    vein, anterior, 324; posterior, 324
  Auriculotemporal nerve, 373
  Auriculoventricular septum, 274
  Axillary artery, 294
    border, 63
    nerve, 388
    vein, 318
  Axis, 15
  Azygos vein, 316

  Backbone, 1
  Back, fascia of, 126
    muscles of, 115, 123; dissection of, 442
  Basilar artery, 291, 292
  Basioccipital bone, 22
  Basisphenoid bone, 25
  Biceps brachii, M., 165, 438, 439
    femoris, M., 194, 444
  Bicipital arch, 166
    groove, 66
    tubercle, 64
    tuberosity, 67
  Bicuspid valve, 279
  Bile duct, 241
  Biventer cervicis, M., 132, 443
  Bladder, 256
    arteries of, 307
    ligaments of, 219, 257
  Blind spot, 414
  Blood vessels, 280
    dissection of, 456
    injection of, 456
  Body cavity, 217
  Body muscles, 115
  Bones, 1
    ear, 423
    head, 21
    pelvic extremities, 76
    preparation of, 430
    sesamoid, 73, 80, 86
    study of, 431
    thoracic extremities, 62
  Bony labyrinth, 425
  Brachial artery, 296
  Brachialis, M., 166, 438, 439
  Brachial plexus, 386; dissection of, 467; vein, 318
  Brachioradialis, M., 173, 438
  Brachium conjunctivum, 348, 349
  Brachium, muscles of, 164
    pontis, 347, 348, 349
    quadrigeminum inferius, 351, 354; superius, 351, 354
  Brain, 339
    arteries of, 289, 291
    diagrams of, 343
    dissection of, 464
    preparation of, 462
    preservation of, 462
    removal of, 462
    study of, 464
    veins of, 324
  Breast, muscles of, 144; dissection of, 437; nerves of, 387
  Broad ligament, 264, 266
  Bronchi, 252
  Bronchial arteries, 283
    veins, 318
  Buccæ, 222
  Buccal cavity, 221
    nerves, 377
  Buccinator, M., 106, 435
    nerve, 374
  Bulbocavernosus, M., 271, 454
  Bulbourethral glands, 261
  Bulbus olfactorius, 362
    urethræ, 261
  Bulla, auditory, 32, 55
    tympanic, 32, 55
  Burdach, column of, 337, 345

  Cæcum, 238
  Calf of leg, muscles of, 203
  Calcaneometatarsalis, M., 215, 445
  Calcaneus, 82, 83
  Callosal sulcus, 362
  Canal, alimentary, 221
    anterior palatine, 41
    condyloid, 24, 58
    facial, 35, 58
    Hunter’s, 311
    hypoglossal, 24, 58
  Canalis adductorius, 311
    facialis, 35, 58
  Canal, lachrymal, 40, 54, 410
    nasolachrymal, 40, 47, 54, 410
    of Huguier, 376
    posterior palatine, 45, 46, 54, 56
    pterygoid, 27, 56, 59
    sacral, 8
  Canals, semicircular, 425, 426
  Canine teeth, 225
  Caninus, M., 100, 435
  Capitatum, os, 70
  Capitulum, 18, 66
  Capsula lentis, 414
  Capsularis, M., 190, 444
  Capsule of Glisson, 302
    of lens 414
  Caput epididymis, 260
  Cardiac nerves, 380, 405, 406
    plexus, 380, 382, 405
  Cardinal veins, 328
  Carotid artery, common, 283; external, 285; internal, 285
    groove, 26
    plexus, 2