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Title: Technique of Eye Dissections
Author: Woll, Frederic A.
Language: English
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  More Transcriber’s Notes may be found at the end of this text.



  The eye--it cannot choose but see.

  --_Wordsworth._



[Illustration: Brain, showing eyes with muscles removed, optic nerves,
and chiasm.]



  TECHNIQUE
  OF
  EYE DISSECTIONS

  BY

  FREDERIC A. WOLL, Ph.D.,

  _Associate Professor, Department of Hygiene, College of the
  City of New York; Optometry Courses, Columbia University;
  Member of New York State Board of Examiners in Optometry;
  Honorary Member: American Optometric Association; State
  Societies--Alabama, California, Connecticut, Kentucky, Maine,
  Massachusetts, North Carolina, Rhode Island; Local Societies--Lehigh
  Valley Society of Optometrists, Mahoning Valley Optometrists’
  Society, and Optometrists’ Club of Brooklyn_.

  _SECOND EDITION_

  [Illustration]

  NEW YORK
  FREDERIC A. WOLL
  1924



  COPYRIGHT, 1914, BY
  FREDERIC A. WOLL
  _Printed in the United States of America_
  First Edition, July, 1914
  Second Edition, April, 1924


  SCHLUETER PRINTING CO., NEW YORK



  DEDICATION

  THIS LITTLE BOOK IS DEDICATED WITH AFFECTION
  AND ESTEEM TO MY FIRST TEACHER
  IN OPTICS, MY FRIEND FOR YEARS

  ANDREW JAY CROSS

  WHOSE RESEARCH IN THE FIELD OF APPLIED
  OPTICS HAS WON FOR HIM RECOGNITION
  AND HONOR



CONTENTS


                                                                    PAGE

  Preface                                                             13

  Introduction                                                        17

  Removal of Hyaloid Membrane with Contents and Attachments Intact    25

  Canal of Petit, The                                                 35

  Interior of the Eye, The                                            38

  Posterior Half, The                                                 40

  Optic Nerve, The                                                    47

  Anterior Half, The                                                  49

  Iris, The                                                           51

  Cornea, The                                                         52

  Crystalline Lens, The                                               53

  Choroid, The                                                        62

  Retina, The                                                         74

  Sagittal or Vertical Section of the Eye, The                        86

  Papilla, Puncta Lacrimalia, and Nasal Duct, The                     92

  Meibomian Glands and Ducts, The                                     96

  Enucleation of the Orbital Contents, The                            97

  Ophthalmoscopic Examinations                                       106

  Lacrimal Ducts, The                                                112

  Lacrimal Gland, The                                                114

  Capsule of Tenon, The                                              115

  Superior Oblique Muscle and its Pulley                             117

  Other Extrinsic Muscles, The                                       118

  Three Tunics of the Eye, the Hyaloid and its Attachments, The      120



ILLUSTRATIONS


                                                                    PAGE

   0. Brain showing eyes with muscles removed, optic nerves, and
      chiasm                                              _Frontispiece_

   1. Glassware and tools                                             22

   2. The first cut                                                   28

   3. How the point of the scissors is kept away from the underlying
      tissues                                                         29

   4. Half of the sclerotic separated                                 30

   5. Picking up the choroid                                          31

   6. Emptying the eye of its contents                                32

   7. Isolated hyaloid, contents and attachments intact               33

   8. Petit’s Canal                                                   36

   9. Cutting eye into anterior and posterior sections with
      safety-razor blade                                              39

  10. Posterior half showing retinal vessels and choroid              40

  11. Showing network of vitreous                                     42

  12. Tearing retina away from posterior half of eye                  44

  13. Posterior half of eye with retina removed                       45

  14. Excavated posterior half of eye                                 46

  15. Split optic nerve                                               47

  16. Ciliary processes and the lens                                  48

  17. How to pull off vitreous                                        50

  18. Processus Zonuloe                                               54

  19. Onion-like layers of lens removed                               56

  20. Cross section of lens                                           57

  21. Lenses showing the results of different kinds of treatment      60

  22. Puncturing the cornea                                           63

  23. Removing the cornea                                             64

  24. How to separate the choroid from the sclerotic                  65

  25. Cutting away the separated sclerotic                            67

  26. Scraping the choroid free from the sclerotic                    68

  27. The isolated choroid                                            69

  28. Inserting scalpel to loosen lens and cut through vitreous       70

  29. Taking out lens and “core” of vitreous                          71

  30. Squeezing out remaining part of vitreous                        72

  31. Cutting through the iris                                        75

  32. Cutting around the ciliary ring                                 76

  33. Lens, iris, and part of vitreous removed                        77

  34. How to force blowpipe into the vitreous                         78

  35. Bulging out of vitreous caused by blowing air through glass
      blowpipe                                                        79

  36. Showing vitreous removed                                        80

  37. Folding the retina by blowing air at it through blowpipe        81

  38. Suspended retina. Sclerotic ready to be cut away                82

  39. Showing sclerotic nearly all cut away                           83

  40. Isolated retina                                                 84

  41. The beginning of the cutting of the eye for sagittal sections   87

  42. Method of cutting through the crystalline lens                  88

  43. Cutting through cornea to complete the sagittal sections        89

  44. Sagittal section enlarged                                       90

  45. Part of calf’s head showing knitting needles inserted in
      puncta                                                          93

  46. Course of knitting needles showing the course of the
      canaliculi                                                      94

  47. Initial cuts to be made in the skin                             98

  48. First cut in bones of orbit                                     99

  49. All the cuts to be made in bones of orbit                      100

  50. How to pry bone loose                                          101

  51. Dissecting close to bones of orbit                             102

  52. Excavated orbit                                                103

  53. Anterior view of enucleated eye                                104

  54. Side view of enucleated eye. All parts _in situ_               104

  55. Enlarging pupil for ophthalmoscopic inspection                 107

  56. How to get rid of the pucker in the cornea                     108

  57. Window cut in the eye                                          110

  58. Pins inserted in lacrimal ducts                                112

  59. Capsule of Tenon blown up                                      115

  60. Showing the extrinsic muscles of the eye                       118

  61. Cutting through the iris                                       120

  62. Scraping ciliary processes free. Choroid cut around ciliary
  ring                                                               121

  63. Cutting away choroid                                           122

  64. Three tunics, hyaloid, and lens                                123



PREFACE


The aim of this booklet is to present to the eye-specialist, the
teacher, the student, and others interested in the study of the anatomy
and physiology of the eye, some definite methods to follow in the
dissection of that organ.

Most dissections of the eye are not made with the same degree of care
and skill used in the dissections of other organs. In following the
usual method of dissecting eyes, much of the important detail is lost.
Often certain membranes are confounded with others, and wrongly
demonstrated. Furthermore, an eye is merely divided by some
demonstrators into an anterior and a posterior half, a very short time
is spent by the students scrutinizing each half; then the text-book is
turned to, and the anatomy is studied descriptively.

Not enough time has been given to thoroughly dissecting all parts of the
eye. As much time should be given as is necessary to bring out
prominently all its parts. Other organs of the body are more thoroughly
dissected, and, therefore, the student has better opportunity to gain a
clearer comprehension and better understanding of the anatomy and
physiology of those organs. Also, as much time should be given,
proportionately, to the learning of the technique of the dissection of
the eye as is given to the learning of the technique of dissecting other
organs of the body.

Many now make a direct specialty of ministering to those suffering from
errors of ocular refraction, ocular diseases, and ocular reflexes, and
for those specialists, principally, this book is written. It is to
fulfil its mission to them by acting as a guide and as a complement to
the descriptive matter in the text-book. It is sent forth in the hope
that it will tend to create more interest in the study of the practical
anatomy of the eye. It is written with a desire to stimulate the ability
to make careful and intelligent observation. It carries with it, as a
final end, an earnest wish that it may, in some small way, be the means
of opening up to the original researcher, a larger field for the
further study of the most important of the senses--the eyesight.

Most of the dissections explained in the following pages are original;
some, however, are only revisions of old methods.

This opportunity is taken to acknowledge the many helpful suggestions
that were made by Dr. Ivin Sickels, of the College of the City of New
York, and by the late Dr. Edward C. Spitzka, of New York. Thanks are due
Mr. E. F. Howes, of Messrs. Swift & Co., for furnishing the necessary
supply of beef eyes; to Messrs. Lee & Beach, photographers, of New York,
for their painstaking efforts in producing good photographs of the
actual dissections; and to Schlueter Printing Company, of New York, for
their many courtesies and interest in the production of the book.

  FREDERIC A. WOLL.

  _New York, July 21, 1914._



INTRODUCTION


In eye dissections it is unnecessary to have either a large equipment of
instruments or a special room. To have a laboratory at one’s disposal is
but a small added convenience. Not to have it, is no serious hindrance.
The work may be carried on and successfully done in one’s office or in
the home, as well as in class-room or laboratory. If it is true that the
atmosphere of a laboratory adds zeal to the efforts of a worker, but
there is no laboratory available, then reverse the order; let the zeal
of the worker add to the atmosphere of the place in which he is doing
his work.

Two things, among others to be mentioned later, are essential; a table
of convenient height, and a good light, natural or artificial. Both are
but modest needs. Compared with other dissections, there will be found
an absence of offensive odors. Neither are there any repulsive
sensations experienced. Such experiences are quite common when making
other kinds of dissections. This work is clean and attractive. Indeed,
one may even develop a rather keen sense of the æsthetic. Many of the
various parts of the eye, when separated and properly preserved, then
viewed and inspected, are bound to bring forth exclamations of
appreciation and wonderment. One can then better understand the
statement: “When Nature perfected the first eye she took a day off so
she could admire the result of her finest piece of handiwork.”

This does not imply that dissections of the eye tend to develop art
appreciation. Appreciation of the wonderful in Nature’s construction of
the special organs is not, however, to be relegated to a distant point.
Such appreciation is concomitant with the knowledge that comes from
having seen, handled, and examined the object studied.

The orchestra leader must have a good listening and hearing ear. This is
developed in him because he has to exercise constantly his power of
listening and hearing. The dissector who would become proficient in eye
dissections and in anatomical investigations must have a good seeing
eye and a dextrous hand. To acquire these two most valuable aids
necessary to carry on careful inquiry or research, it is essential to
practise using the eye and the hand. Combined with the expertness of
these two, must be the ability to continue one’s efforts in the face of
failure; to redouble one’s efforts to attain success despite the
shortcomings of eye or hand. This simply means practise and patience.
And the one who is without that wonderful virtue, patience, will never
stay long enough with his problem to gain either an observing eye or an
expert hand, or to achieve his end, and thereby reap the full and
pleasing results of his efforts. In order of importance, patience really
precedes dexterity, skill, and observation; and persistence of effort is
a factor not to be entirely outshone by any other virtue. With these
attributes, knowledge of the subject in hand naturally follows.

One reason why eye dissections are easily carried on is because material
can always be readily procured. Any butcher will furnish sheep, pig, or
beef eyes. Or, if one has the time to visit the manager of a
slaughter-house, and make known to him one’s needs, he will supply
enough eyes to carry through a host of interesting dissections and
experiments, and give sufficient material for careful, orderly, and
fruitful study. Perhaps in no other kinds of dissections will the
investigator find so much of interest, or have his efforts crowned with
such abundant and satisfactory results, as in the dissections of the
eye. But no one should try to study all parts of the eye with only one
specimen. To try to do so is an error, and a common one often committed
by both teachers and students. Specimens cost little or nothing, and it
is no more trouble to prepare a half-dozen eyes for dissection than one.
The cost of preparation, too, is but little more for a number of eyes
than it is for one, and may be no more in some instances. Besides,
having enough material on hand saves time in case of a failure. Also,
one can quickly repeat a dissection, and so procure any number of
desired specimens of specific parts, or do over again the same
dissection on another eye just for the purpose of practise, and thus add
to one’s dexterity. It is, therefore, strongly advocated to have plenty
of material on hand before beginning work. Economy here is not even
“penny wise.”

The tools, or instruments, needed are but few in number; an ordinary
scalpel, a pair of blunt tweezers, or forceps, as they are sometimes
called; a pair of sharp-pointed tweezers, a pair of small, sharp-pointed
scissors of about three to three and a half inches in length, and a pair
of large scissors, about four or five inches in length, having one jaw
sharp-pointed and one jaw blunt.

For glassware, any wide-mouthed jar or bottle, such as the ordinary
fruit or jelly jar, will do for preparing material. For clarifying
tissues, or for preserving and keeping them, small, wide-mouthed bottles
or vials should be used. And for temporary keeping, or for purposes of
“running through” various fluids, the regular Stender dishes are most
convenient. A glass graduate is almost indispensable if accuracy in
measuring fluids is desired. (Fig. 1.)

[Illustration: Fig. 1.]

The chemicals needed are few in number and small in quantity: Alcohols
in varying strength, which can be made by diluting a 95 per cent.
alcohol, and keeping an absolute alcohol on hand. A few ounces of
formaldehyde will make enough solutions of different strengths to be
sufficient for the preparation and keeping of many specimens. Of other
chemicals, such as xylol and cedar oil, only small quantities are
needed; enough to cover a specimen. Fifteen to twenty cents worth of
each will be an ample supply to keep on hand. All of these may be
procured at any large drug store, and are the only chemicals required
for doing the dissections as explained in this book.

Before further advance is made, it will be best to state that this work
deals only with methods for dissecting the various parts of an eye, and
is primarily intended to aid in the study of the anatomy and physiology
of the eye by being used in conjunction with such books as “Gray’s
Anatomy,” “A Text-Book of Physiology,” by Howell, “The Anatomy and the
Physiology of the Eye,” by Brown and Zoethout, and similar other works
of authority. However, if it is desired to acquire only specimens, then,
of course, no other works are necessary, and the matter contained herein
is sufficient to enable one to procure just what is wanted.

It is also wise to state here that since human eyes are hard to procure,
and not available in large quantities, one must resort to the use of
the eyes of animals, which are procurable in large quantities, and which
may be used without “feelings” in the matter. Though there is a
difference between the eyes of human beings and the eyes of other
animals, the difference is slight and of minor importance when compared
with the similarity of the more important parts.



TECHNIQUE OF EYE DISSECTIONS



REMOVAL OF THE HYALOID MEMBRANE WITH CONTENTS AND ATTACHMENTS
INTACT[1][2]


One of the easiest and most satisfactory dissections to attempt is the
isolating of the hyaloid membrane with its contents and its attachments.
The success one meets with in making this dissection will surely prove a
strong incentive for making all the rest. For these reasons this has
been placed first in this arrangement.

In eye dissections it is quite customary, in giving directions for
dissections, merely to mention the hyaloid membrane and its relations
with other parts of the eye. Rarely is there any attempt made to isolate
it. Often, too, the retina is mistaken for the hyaloid, and the retina
then wrongly demonstrated as being attached to the choroid. Of course,
it is impossible to separate the hyaloid from the vitreous; but a
dissection can be made which, when placed in a glass of some kind, will
show the hyaloid. If the following simple technique is carefully
observed, the membrane, with all its connections, can be easily
separated from certain other parts of the eye. Opportunity for thorough
study and observation will then be made extremely easy.

Procure the eye of either a sheep or a bullock. Instead of following the
usual procedure of hardening in any one of the several solutions used
for the purpose of toughening the ocular tissues, place the eye in a
cool place and permit it to collapse a trifle. Usually two or three days
is a sufficient length of time to accomplish the result.

Experiments have shown that if an eye is too fresh the ciliary
processes will not be easily detached from the hyaloid (zonular
processes), and if the eye has been in a preserving fluid, the same
result will follow. A sheep’s eye will make a better specimen even if it
is small, because the ciliary processes are more easily separated from
the zonular processes. If a bullock’s eye is used, it must be left in a
cool place a day or two longer than in the case of a sheep’s eye, in
order to permit a long enough time to elapse to allow disintegration of
the eye to take place sufficient to have the two processes separate
easily and cleanly.

[Illustration: Fig. 2--Making the first cut. (Page 27.)]

[Illustration: Fig. 3--Showing how the point of the lower jaw of the
scissors is to be kept away from the underlying tissues. (Page 27.)]

[Illustration: Fig. 4--Showing about half of the sclerotic separated.
(Page 29.)]

With a pair of dissecting forceps pinch up the sclerotic about 5 mm.
anterior to the equator. With a pair of small, fine-pointed scissors,
make an incision. (Fig. 2.) Next hold the eye in the left hand without
exerting any pressure. Insert the point of the scissors into the
incision which has been made, and cut. Be careful to keep the point of
the scissors close to the sclerotic or an untimely puncturing of the
choroid will occur. (Fig. 3.) Continue the cutting on a line parallel
to the equatorial meridian and about 5 mm. anterior to it until about
half the sclerotic has been separated. In cutting, always move the point
of the scissors forward with a slight oscillating lateral movement.
(Fig. 4.) While doing this, partly suspend the eyeball from the point of
the scissors. Doing these things will tend to loosen the choroid from
the sclerotic and prevent puncturing too soon the former mentioned
membrane. Now apply pressure in such a manner that the lips of the cut
sclerotic will gap. Into this put the point of the scissors and very
carefully pick up the choroid and the retina with the point of the
scissors and cut them. (Fig. 5.) If the choroid alone has been picked
up and separated, the retina will show milky white or yellowish white
underneath. The retina must then also be separated. Care must be taken
not to go deeper than the retina or the hyaloid may be damaged. Continue
the cutting of the choroid and the retina for a distance of about 20 mm.
Apply enough pressure occasionally so that the vitreous will be forced
upward and above the cut choroid and the retina. This will show whether
any strands of the two membranes have been left uncut. If the separation
is complete for the distance specified above, invert the eyeball,
squeeze and shake gently over some receptacle, such as a Stender dish,
three-fourths filled with a 2½ or 5 per cent. solution of formaldehyde,
and the hyaloid membrane containing the vitreous, its attachments,
suspensory ligament to the lens capsule, and lens, will drop out intact,
as when one empties the contents of an egg. (Fig. 6.)

[Illustration: Fig. 5.--Picking up the choroid with the point of the
scissors.]

[Illustration: Fig. 6--A. Hyaloid, vitreous, and lens ready to drop out
of the eyeball.]

[Illustration: Fig. 7--Photograph of dissected hyaloid membrane (A),
with pigmented indentations of the ciliary processes, the suspensory
ligament (B), and the crystalline lens in its capsule (C). (Page 34.)]

Many times a considerable amount of pigment from the second tunic will
remain attached to the _processus zonuloe_. This pigment may be easily
removed by scraping it off with the sharp edge of the scalpel or by
brushing it off with a soft, wet tooth-brush.

It is unwise to use alcohol as a preservative because it produces an
almost immediate opaqueness and hardness which spoils the specimen for
further study.

This description may give the impression that the dissection is a
lengthy one; however, it can be done by an expert in two or three
minutes; by a beginner in five or six minutes.

For purposes of demonstration or study the specimen should be placed in
a small bottle or a vial containing a 5 per cent. solution of
formaldehyde. It can then be examined with hand lens or microscope.
(Fig. 7.)

  [1] Approved as an original article in _The Anatomical Record_,
  September, 1912.

  [2] This dissection, and several of the following, appeared in _The
  Optical Journal and Review_, beginning with the issue of January 16,
  1913.



THE CANAL OF PETIT


The canal of Petit is a “triangular space around the circumference of
the lens.” That it can be “inflated through a fine blowpipe inserted
through the suspensory ligament,” is the usual direction given. However,
the ordinary “fine blowpipe” is much too large and too dull to be
inserted through the suspensory ligament. Take a long medicine-dropper
(5 or 10 cents at a drug store), or a pipette, and heat it until it is
red hot over an alcohol lamp or a Bunsen burner; hold one end with one
hand and the other end with a pair of tweezers. As the glass becomes
white hot pull the tube apart. This will leave the places of separation
pointed and sharp-edged. Use the larger of the two pieces. Sometimes the
point or tapering end of the tube is too long and the bore too small.
All that is necessary is to first mark off with a file the length to be
broken off, and then that length may be snapped off, leaving a
sharp-edged, tapering point.

[Illustration: Fig. 8--A. Glass blowpipe. B. Petit’s canal.]

After having completed the first dissection (the hyaloid, contents and
attachments), and the specimen has been in the formaldehyde solution for
ten days or two weeks, it will have become hard and tough enough to
stand a considerable amount of rough handling. If the specimen has been
kept in a large receptacle, such, for instance, as a jar, remove it
with a spoon; if in a small jar or vial, empty out the fluid, then
slide the specimen out on whatever has been prepared to receive it. Turn
it so that the lens will be uppermost. Find the suspensory ligament in
the Zone of Zinn. Insert the pointed end of the glass tube, close to the
lens, and blow gently until the canal shows its sacculated construction
by filling with air, giving the appearance of a lot of little bubbles
surrounding the periphery of the lens. (Fig. 8.) It may be necessary to
move the blowpipe in and out in order to find the canal, all the while
blowing steadily through the tube.



THE INTERIOR OF THE EYE


For the study of the interior of the eye and its contents _in situ_
either a fresh or a hardened eye will do; a hardened eye is preferable.
In the dissection for isolating the hyaloid membrane, vitreous, lens,
and other parts, the anterior and posterior halves of the evacuated eye
may be separated entirely, and each half studied. However, the choroid
and the retina will be more or less mutilated, and the vitreous and
other parts will be removed. The absence of these parts will prevent one
from receiving a definite idea of their anatomical relationships.
Therefore, it is better to work with an entire and complete eye.

[Illustration: Fig. 9--Showing method of cutting eye into anterior and
posterior sections with safety-razor blade.]

Remove all the muscles and fatty tissues from the outside of the globe;
then cut it in half through the equator, thus dividing it into an
anterior and a posterior half. The cutting of the sclerotic, as well as
the underlying tissues and the vitreous, should be done with the large
scissors; using a knife or scalpel will tend to disturb the positions of
those tissues or so tear them that they will not be of much use for
purposes of study. An ordinary safety-razor blade makes an excellent
instrument for separating the eye into two halves, because it cuts
through the tissues without tearing them in any way. (Fig. 9.) The
rather dark colored, viscid fluid that escapes when the eye is halved
is the perichoroidal lymph, not the aqueous, as is sometimes stated.


THE POSTERIOR HALF

The posterior half is taken first because it is the simplest and easiest
of the two halves to dissect. In this half of the eye the retina may be
readily seen through the vitreous; the choroid and its apparent
iridescent colors through both vitreous and retina. (Fig. 10.) Remove
the vitreous by simply tilting this half of the eye, and with the finger
push out the vitreous.

[Illustration: Fig. 10--The retina, retinal vessels, and iridescent
choroid showing through the vitreous.]

Sometimes the vitreous will adhere very closely to the retina. This
occurs especially when the eye has been in formaldehyde for a long time.
In such a case the removal of the vitreous without injuring the retina
requires patience and care. The use of the scalpel and the scissors may
become necessary. Another very good way to remove the vitreous is to
take hold of the sclerotic, turn it so that the vitreous is downward,
and then shake gently until the vitreous separates itself from the
retina and, drops out. After the vitreous has been removed, notice its
glassy appearance; hence its name--hyaloid body. Try to pull it apart
with the fingers, and it will be noticed that it seems to be held
together by more or less of a network of fibres. (Fig. 11.)

[Illustration: Fig. 11--Showing how vitreous seems to be held together
by a network of fibres. (Page 41.)]

Whichever method for removing the vitreous is followed, the retina will
be left rather badly wrinkled and out of place. If the last-mentioned
method, which is really the best of the three described, is the one
adopted, the retina will be left in an entirely collapsed and folded
form. In any case, to straighten out the retina against the choroid,
immerse the whole posterior half in water, inside uppermost. The retina
will then slowly unfold itself and lie flat against the choroid. With
the tweezers remove the whole half from the water; tilting it slowly to
empty it of all the water, and, having done so, turn it down upon the
table rather forcibly in order to help it drain itself of all the water.

Notice the thinness of the retina, and, also, that the seeming
iridescence of the choroid shows through. The optic disc, which is the
point of entrance of the optic nerve, and the optic cup are easily
recognized, though neither will be seen as large as when viewed in the
living eye with an ophthalmoscope. The blood vessels of the retina, as
they ramify outward or forward, after their entrance through the optic
nerve through which they pass, are also very plainly seen. A closer
inspection will show, in the very centre of the “entrance” of the optic
nerve, a whitish, pointed vessel, about 1 or 2 mm. long. That is the
sloughed-off and atrophied end of the hyaloid artery, which, when the
eye was in an embryonic state, ran forward from the central artery of
the retina through the hyaloid canal to the posterior surface of the
lens. With the forceps pick up the peripheral edge of the retina, and,
by pulling gently upward, tear it away from its apparent place of
attachment to the “entrance” of the optic nerve. (Fig. 12.) When this
has been done, there will be seen some threads protruding from the
optic nerve. Filling the half with water will tend to separate these
strands, which are optic-nerve elements.

[Illustration: Fig. 12--Picking up the retina in order to tear it away
from the entrance of the optic nerve.]

[Illustration: Fig. 13--The lighter area is the field of iridescence of
the choroid.]

After the removal of the retina, the iridescence of the choroid
(_tapetum lucidum_) (Fig. 13) may be examined with a hand lens, or,
after its removal, a piece may be cut and placed under a microscope.
This iridescence is, of course, not present in the human eye.
(“Physiology of the Senses,” McKendrick & Snodgrass, page 101.)

[Illustration: Fig. 14--Excavated posterior half of the sclerotic.]

After the choroid is removed, which is accomplished in the same manner
that the retina is removed, the inner side of the sclerotic is laid bare
to view. The brownish color is mostly due to the presence of a small
amount of pigment in the cells of one of the inner layers, it is also
due, to a slight extent, to the staining influence of the perichoroidal
fluid. (Fig. 14.)


THE OPTIC NERVE

[Illustration: Fig. 15--Enlarged to show the entrance of the optic
nerve. (Page 48.)]

The excavated posterior half may be used now to show and to study the
construction of the optic nerve. In cutting the optic nerve away from
the sclerotic leave at least 5 mm. of the sclerotic attached. It will
make handling easier. With the thumb and forefinger of the left hand
hold the nerve in such a way on the table that it will be straightened
out lengthwise, and then, using the scalpel or a safety-razor blade,
the latter being preferable, cut the nerve in two longitudinally. (Fig.
15.) The cutting must be done with one movement, otherwise the nerve
will be hacked, and will not make a good specimen. This specimen will
show the way the nerve fibers are arranged. A cross section should be
cut from the optic nerve of another eye, and then the two sections
should be compared. The cross section will show the sheath of the nerve
a little better than will the longitudinal section.

[Illustration: Fig. 16--Showing ciliary processes and crystalline lens.]

In cutting the longitudinal section, one is sometimes so fortunate as to
cut through the central blood vessels of the retina. These vessels will
show up then as a rather thin dark streak about 5 or 6 mm. long.


THE ANTERIOR HALF

The anterior half will show the lens _in situ_, the ciliary processes,
the posterior aspects of the iris and the lens, the corona ciliaris, the
orbicularis ciliaris, and the ora serrata. (Fig. 16.) If the eye has
been cut in two too far forward of its equator, the ora serrata will not
be present. The ciliary processes and posterior aspect of the lens may
be seen to better advantage when the anterior half of the vitreous is
removed. This is done with the dull-pointed tweezers, by catching hold
of the vitreous at any part of its free or cut margin, and stripping it
off both the ciliary processes and the lens, using a prying, pulling
movement to do so. (Fig. 17.) The two layers of the pigment cells, pars
ciliaris retinae, which cover the inner surface of the processes, may
be removed by picking them away carefully with the tweezers. The
processes then will be seen to be a whitish color. The pupillary edge of
the iris rests upon the capsule of the lens, but the nearer the approach
is to the choroidal edge the farther the iris is from the lens; thus are
formed the anterior and the posterior chambers of the eye. The
dissection of the sagittal section of the eye, explained further on,
will show these two chambers in section. One will gain a much clearer
conception of their construction in that section than in the “anterior
half” specimen.

[Illustration: Fig. 17--Anterior half, showing how to pull off vitreous.
(Page 49.)]

Now, remove the lens, using the point of the scalpel to cut through the
suspensory ligament close to the lens. When this has been done there
will be seen in the anterior chamber a thin, watery liquid--the aqueous
humor.

The corona ciliaris and orbicularis ciliaris may be better seen and
studied if viewed through a hand lens.


THE IRIS

To see the iris, take hold of the cut edge of the choroid, and, gently
pulling, separate it from its attachment to the corneo-scleral junction.
The white ring on the anterior surface of this part of the second coat
of the eye is the ciliary ring. With a scissors, cut around this ciliary
ring at its outer edge. This specimen will show the anterior surface of
the iris, and on the posterior side it will show the close relationship
between the iris and the ciliary processes. A hand lens will help
greatly to bring out the very interesting fine points.


THE CORNEA

After the anterior portion has had everything removed from it there will
be left nothing but the first coat or tunic of the eye--the anterior
portion of the sclerotic and the cornea. The way the cornea seems to fit
into the sclerotic is not quite as one is led to believe when told that
it fits into the sclerotic much the same way in which a watch crystal
fits into a watch.[3] Holding this part of the eye up to a strong light
one will see that the sclerotic seems to overlap the cornea in the
vertical axis.

By using the tweezers the cornea may be split. Nothing in the way of
locating its layers can be recognized, however, unless a section is made
for microscopic examination. The epithelial may be scraped off when the
cornea is a trifle dry. This is the ocular epithelium reduced to a layer
of flattened cells.


THE CRYSTALLINE LENS

If the preceding dissections have been done, the crystalline lens will
already have received some notice. To study the lens properly one should
use an eye that has not been hardened and also an eye or the lens of an
eye that has been in a 5 per cent. solution of formaldehyde for about
two weeks.

The lens in the unhardened eye will prove too friable to permit much
handling. The dissection should be made, however, in order to give
opportunity to notice the crystalline clearness of the lens substance,
its great magnifying power, its attachments, its capsule, etc. For this
purpose it is necessary to proceed only as in the dissection for the
“hyaloid membrane, etc.” That is, use an eye that has been kept in a
cool place for several days, and then open it, and remove hyaloid,
vitreous, and lens intact, as in the first dissection taken up in this
book. To examine the specimen in detail, turn it so the lens will be
uppermost. (Fig. 18.)

To remove the lens it is necessary to separate the suspensory ligament,
using for this purpose the small-pointed scissors. The capsule may be
removed by picking it up on the periphery of the lens, and stripping it
off. It will peel off about the same way that the outer skin of a bean
or pea does.

[Illustration: Fig. 18--Enlarged to show the processus zonuloe. (Page
53.)]

The tri-radiate lines on the posterior and the anterior surfaces of the
lens will not be as clearly discernible as in the lens coming from the
hardened eye. Close inspection and the use of a hand lens will help
bring them out more clearly.

Now, with the point of the scalpel try to separate the outer layers
(cortex) from the harder inner layers (nucleus). This will not prove
very successful but is suggested for the purpose of comparison when the
same thing is done to the hardened lens.

It will be found that the lens after having been in the formaldehyde
solution is no longer crystal like, but more or less translucent. When
viewed from either the anterior side or the posterior side, the
tri-radiate lines on each surface will be seen to begin at the poles of
the lens and radiate outward toward the lens equator. Holding the lens
up to a strong light will show that though the lines on either surface
form angles of 120 degrees, the angles formed by the lines on one side
with the lines on the other side are 60 degrees. On the anterior surface
of the lens the vertical line extends upward from the pole; on the
posterior surface downward from the pole.

To study the laminated structure of the lens, it is best to boil the
lens. The best way to do that is to drop the lens from either a hardened
or unhardened eye into boiling water. Let it boil in the water for about
two and a half to three minutes. Longer than that time will cause the
lens to be put out of shape, and make it so fragile that it can no
longer be handled without having it fall apart. If the lens comes from
an unhardened eye it might be best to boil it not more than about two
minutes.

[Illustration: Fig. 19--Showing the way the onion-like layers of the
lens may be peeled off.]

Insert the point of the scalpel carefully at one of the poles, and lift
gently in the direction of one of the radiating lines. This will tend to
raise one of the concentric layers, which can be easily peeled off.
Repeat this in the direction of the other two radiating lines.
Examining, with a hand lens, the exposed surfaces and the layers, as
they are taken off, will show the arrangement of the lens fibres, and
will also show plainly their directions. (Fig. 19.) To get another view
of the onion-like layers of the lens, cut through it with a safety-razor
blade, either longitudinally or equatorially. (Fig. 20.) The better way
is to have enough lenses to make one of each kind. Never try to work
with only one piece of material. If the lens is first stained with
chromic acid the layers may be seen better, or, a simpler way is to drop
the lens, before cutting it in two, into a carmine solution; red ink
slightly diluted, will do.

[Illustration: Fig. 20--Section through lens showing its concentric
layers.]

A lens that has been boiled and partly dissected may be placed in a 5
per cent. formaldehyde solution, and kept indefinitely. The lens fibres,
concentric layers, and lens laminae in such a specimen will always be
interesting.

A lens that has lost its transparency because of hardening in
formaldehyde or boiling may be made clear and nearly transparent again
in the following way: First: Place the lens in a 50 per cent. alcohol
for several hours. Second: Remove the lens, and let it drain on a piece
of blotting-paper; then place it in a 75 per cent. alcohol. Third:
Remove the lens, as before, then place it in an 85 per cent. alcohol.
The lens may be left in this alcohol from ten to twelve hours, after
which length of time it should be removed and drained. Fourth: Place the
lens in an absolute alcohol, and leave it there for ten or twelve hours.
Several hours longer will not injure the lens, nor interfere with the
success of the work. Fifth: Remove the lens from the absolute alcohol.
Place it upon a piece of blotting-paper, moving it to another place on
the blotting-paper whenever the paper around the lens seems to have
taken up as much moisture as it can hold. Be sure that the lens has
given up nearly all, if not all, moisture. “Running through the
alcohols,” as this process is called, is for the purpose of dehydrating
the tissue. It will be on the side of safety to let the lens lie exposed
on the blotting-paper for an hour. Sometimes, if the capsule has not
been removed, a small quantity of alcohol will remain between the lens
and the inner surface of the capsule. This must be removed. It may be
done by either puncturing the capsule with a pin or needle, and
squeezing out the fluid, or by removing the capsule entirely. The latter
is preferable.

Now drop the lens into xylol. Benzine will answer, though it will not
produce quite so clear a lens as the xylol does. At the end of 24 or 36
hours the softer cortex will show quite clear, while the harder nucleus
will be still cloudy. At the end of a week the whole lens, if it is a
small one--pig, calf, sheep--will have become quite clear and
transparent; if from a beef eye it will take longer. It sometimes takes
nearly two weeks. In the case of a boiled lens it will take much longer
to clear; it may take a month.

Cedar oil may also be used for the purpose of clarifying or “clearing”
the lens. Harden in the usual way, run through the alcohols, and then
place in cedar oil. The oil, however, will stain the lens a yellowish
brown, and the lens will not be as transparent and clear as when xylol
is used.

[Illustration: Fig. 21.

A. Lens hardened in formaldehyde.

B. Lens hardened in formaldehyde, run through the alcohols, and cleared
in xylol.

C. Lens hardened in formaldehyde, run through the alcohols, and cleared
in cedar oil.

D. Boiled lens.]

The longer a lens is left in either of these two clarifying fluids the
harder and smaller it will become. At the end of a month or six weeks
the lens will have become so hard that it can no longer be cut through
with a knife. If it is desired to halve it, a scroll saw will be found
to be the best thing to use for this purpose. (Fig. 21.)

  [3] “Anatomy and Physiology of the Eye,” Brown & Zoethout.



THE CHOROID


Select an eye that has had a long part of the optic nerve left on it and
place it into a 5 per cent. solution of formaldehyde. Leave it in that
solution for from two to three weeks. That period of time in the fluid
will be sufficient to permit the choroid to become sufficiently
toughened and hardened. Leaving it in the solution longer than that
length of time will not injure the eye in any way.

[Illustration: Fig. 22--Showing how to puncture the cornea. (Page 62.)]

[Illustration: Fig. 23--Removing the cornea. (Page 63.)]

[Illustration: Fig. 24--Showing method of inserting the scalpel to
separate the choroid from the sclerotic.]

After having removed the eye from the formaldehyde, wash it for a few
moments in running water. This will remove the preserving and hardening
fluid from the surface, and will save the hands a little from the
effects of the fluid. Next remove all the muscles and fatty tissues from
the sclerotic. After that has been done, puncture the cornea with the
pointed jaw of the scissors about 2 mm. from the corneo-scleral
junction. (Fig. 22.) Then proceed to cut the cornea away, being careful
not to lacerate the choroid or the iris. (Fig. 23.) The escaping aqueous
humor will flow over the eye and make it very slippery, and, therefore,
difficult to hold. Dip the eye in water, wash it, and then take it out
and thoroughly dry it with a cloth. This procedure is absolutely
necessary, and, if omitted, will surely result in the dropping of the
eye about the time the work on the specimen is nearly finished. Insert
the scalpel between the peripheral edge of the exposed iris and what is
left of the cornea. With the back edge of the scalpel, gently loosen the
choroid from the inner side of the corneo-scleral junction to which
part it is not securely attached. (Fig. 24.) This requires only ordinary
care, and but little skill other than that necessary to always keep the
scalpel close to the inner surface of the sclerotic. When the
choroid-iris edge has been detached from the inner side of the
corneo-scleral junction, the weight of the contents of the second tunic
will cause it to sag and give opportunity to easily separate, with the
back edge of the scalpel, the choroid from the sclerotic for about a
distance of from 8 to 10 mm.

It has been the method in the past to force water through a blowpipe
between the sclerotic and the choroid, in order to separate the
attachments. It has also been the method to work under water when
wishing to expose or isolate either the choroid or the retina. It is
unnecessary to do either of these two things.

When the sclerotic has been loosened from the choroid for about 10 mm.
back from its cut edge around the eye, carefully cut the loosened part
away. (Fig. 25.) Then loosen the choroid as far back as to within 1 cm.
of the optic nerve. Cut the separated sclerotic away. It will be well to
state here that during this dissection the specimen should not be lifted
from the table. Keep the eye resting on the table all the time, and
never lift it by holding it suspended from the optic nerve. Loosening
the choroid from the sclerotic up to this point is a very easy matter;
ordinary precaution is all that is necessary to prevent puncturing the
choroid with the scalpel, just be sure to remember to keep the point of
the scalpel close to the sclerotic.

[Illustration: Fig. 25--Cutting away the sclerotic after it has been
loosened from the choroid, as shown in Fig. 24.]

[Illustration: Fig. 26.--Showing how to scrape the choroid free from the
sclerotic near the optic nerve.]

To remove the remaining part of the first coat is a little more
difficult, and needs a little more care. Hold the optic nerve in the
left hand, and pull it so that the sclerotic will pull away from the
choroid. Then, using the cutting edge of the scalpel, scrape the choroid
loose from the sclerotic close up to the entrance of the optic nerve.
(Fig. 26.) Do not separate the optic nerve from the choroid. Cut away
the remainder of the sclerotic close up to the optic nerve and the
choroid will be free. (Fig. 27.)

[Illustration: Fig. 27--Showing the choroid, the optic nerve still
attached, the ciliary ring, and the ciliary nerves.]

[Illustration: Fig. 28--Showing method of inserting scalpel in order to
loosen the lens and cut through the vitreous.]

To get a perfect specimen and completely isolated choroid, it must be
emptied of its contents. Insert the scalpel between the lens and the
iris, force it on through, and in such a manner as to keep the scalpel
close to the ciliary processes. (Fig. 28.) Cut the vitreous around the
processes. Push the scalpel further into the vitreous, and cut out the
central part of it, just as one would cut out the core of an apple.
(Fig. 29.) Remove the scalpel, pick out the lens and the cut centre of
the vitreous with the broad-point tweezers, holding the choroid a trifle
suspended by the optic nerve. The remaining part of the vitreous may be
broken down by cutting with the scalpel, and by squeezing and crushing
with the fingers of both hands. (Fig. 30.) The choroid will be tough
enough to stand this treatment provided the pupil is left clear and open
to prevent inter-choroidal pressure. After the vitreous has been removed
the choroid will be left in a greatly collapsed condition. Dropping it
into water and letting it fill up will make it resume its original
shape immediately. The retina does not always come out with the
vitreous. In such a case, the tweezers may be used to pick out the
retina when the choroid is in a collapsed condition.

[Illustration: Fig. 29--Taking out the lens and “core” of the vitreous.]

[Illustration: Fig. 30--Showing how to squeeze out the remaining part of
the vitreous (A) from the choroid. (Page 71.)]

This specimen will show the vena vorticosa, the ciliary nerves, and
their way of ramifying, and the long ciliary arteries, which run
opposite each other and which may be recognized by their rather
colorless, tubular appearance. The evacuated choroid makes an excellent
specimen and one easily examined. Place it in a 3 per cent. solution of
formaldehyde, and then examine with a skiascope, an ophthalmoscope, or
by “oblique illumination.”

This dissection is wholly original, and may be done in about five
minutes. The old technique for doing it required at least an hour of
time with the possibility of procuring one perfect specimen in every six
or seven. The technique as given here will make it possible to do the
work in not longer than five or six minutes for the beginner, and about
four minutes for the expert.



THE RETINA


Isolating the retina from the other tissues requires considerable
patience and dexterity. When the retina has been removed and placed in a
special receptacle, it will be found that the specimen is well worth the
little amount of time spent in making it. Previous techniques, even the
writer’s own, sometimes took nearly two hours to do, and rarely was the
retina isolated without puncturing or tearing it; perfect specimens were
almost impossible. The following method will assure one of success in
nearly every instance. Failures are almost impossible. Punctures,
perforations, tears, etc., are rare. The beginner should isolate the
retina in about six to seven minutes; the expert in about four and a
half to five minutes.

Select an eye with a long optic nerve, and prepare it for this
dissection by placing it in a 10 per cent. solution of formaldehyde for
about ten to fourteen days, but no longer. If it is left in the
hardening fluid longer than that length of time, it will interfere with
the easy removal of the vitreous.

[Illustration: Fig. 31--Cutting through the iris. (Page 77.)]

[Illustration: Fig. 32--Showing how to cut around the ciliary ring.
(Page 77.)]

The first part of this dissection is the same as the beginning of the
dissection for the isolation of the choroid. Remove all the outside
tissues first, and then the cornea, and about 10 mm. of the sclerotic,
as described in the preceding dissection. (See Figs. 22, 23, 24, and
25.) That will lay bare the iris and a few millimetres of the choroid.

[Illustration: Fig. 33--Lens, iris, and part of vitreous removed. (Page
78.)]

After that has been done, turn the eye so the iris will be uppermost.
With the tweezers pick up the pupillary margin of the iris, and with the
fine-pointed scissors cut through the iris and the ciliary processes
(Fig. 31); separate both from the choroid by cutting close to the
posterior edge of the processes. (Fig. 32.) In doing that, cut partly
through the vitreous also, but be careful not to injure the peripheral
edge of the retina--ora serrata. After the iris has been separated from
the choroid, cut completely through the vitreous in such a way that the
lens will also be removed with the iris. (Fig. 33.)

[Illustration: Fig. 34--Showing how to force glass blowpipe (A) into
vitreous (B). (Page 80.)]

[Illustration: Fig. 35--Showing bulging out of vitreous caused by
blowing air through glass blowpipe. (Page 80.)]

[Illustration: Fig. 36--Showing the vitreous (A) removed.]

Holding the eye suspended by its optic nerve, force the glass blowpipe
through the vitreous until it all but touches the posterior part of
the retina (Fig. 34); blow gently at first, increasing the pressure
until the vitreous suddenly bulges outward. (Fig. 35.) If the iris has
been cut away close to the ora serrata, the vitreous will not only bulge
forward, but it will fall out. If, however, it does not detach itself at
once, insert the scalpel close to the choroid and with its flat side
press downward until a separation occurs. Do not let the vitreous drop
out too suddenly, because it may tear the retina. Let the vitreous
detach itself slowly by the force of its own weight, though it will be
well to hold some of its weight on the scalpel. (Fig. 36.)

[Illustration: Fig. 37--A. Showing retina folded upon itself by blowing
air at it through the glass blowpipe. (Page 83.)]

[Illustration: Fig. 38--A. Showing folded retina suspended from its
attachment, so sclerotic and choroid may be easily cut away. (Page 83.)]

After the vitreous has been removed, turn the eye upward, and by blowing
strongly through the blowpipe at the marginal edge of the retina, turn
the retina upon itself. Repeat this until the retina lies in a small
wrinkled lump at the “bottom” of the posterior part of the eye. (Fig.
37.) Invert the eye (Fig. 38) and cut away both the choroid and the
sclerotic close to the optic nerve. No care need be taken in doing this
until the scissors come close to the optic nerve. (Fig. 39.)

[Illustration: Fig. 39--Showing the sclerotic nearly all cut away.]

[Illustration: Fig. 40--Isolated retina, with optic nerve attached.]

After the choroid and the sclerotic have been cut away, drop the retina
into some water, and it will slowly unfold itself by “ballooning” out
into a perfect and beautiful specimen. (Fig. 40.) But, if it is desired
to study the specimen closely, it is better to suspend it in a jar or
bottle made of thin glass, and containing a 5 per cent. solution of
formaldehyde. Remember that the retina is a delicate membrane in any
state; the slightest rough handling may cause it to be torn, or
otherwise damaged. If the vessel, in which the specimen has been placed
and suspended, has enough preserving fluid to completely fill it, and it
is firmly stoppered, the whole thing may be inverted, and turned in any
direction, even abruptly, without fear of damaging the retina. This way
of keeping the retina will give opportunity to inspect and study the
inside as well as the outside of the membrane; the blood-vessels, and
other important parts easily recognized.



THE SAGITTAL OR VERTICAL SECTION OF THE EYE


Place an eye in a 5 per cent. solution of formaldehyde for about two
weeks. If the eye is kept in that solution longer than that time, the
lens is apt to become so hard that in cutting it the capsule and
suspensory ligament will be torn, and the lens will then become
detached; if for a shorter space of time, the lens and other tissues
will be so soft that all may be so badly torn or lacerated, that a
perfect specimen will not be possible.

It sometimes happens that in keeping a number of eyes together in a
vessel for the purpose of hardening them in the formaldehyde solution,
the corneas of some will be crushed in. For this dissection, select an
eye that has the cornea in perfect condition.

Remove all the outside tissues with the scissors, being particular to
have the region immediately surrounding the optic nerve perfectly clear
and clean. If the optic nerve is longer than 5 mm., cut it off to that
length.

[Illustration: Fig. 41--Showing the beginning of the cutting of the eye
for sagittal sections.]

[Illustration: Fig. 42--Showing method of cutting through the
crystalline lens.]

To cut the eye in two, use a safety-razor blade; never a scalpel. The
latter is too thick, too dull, and too clumsy a tool. Begin by cutting
through the optic nerve; dividing it as nearly as possible into halves.
(Fig. 41.) Continue cutting through the sclerotic and all underlying
tissues, stopping at the corneo-scleral junction, but do not, during
this procedure, even touch the lens. After the eye has been thus partly
separated into, as nearly as possible, two equal parts, lay it down upon
the cornea, and, holding the razor blade in the forefingers and thumbs
of both hands, cut the lens in two by forcing the blade down through it.
(Fig. 42.) Partly open the cut eye to allow one jaw of the large
scissors to enter, turn the eye over so the cornea will rest on that
jaw, and then cut through the cornea. (Fig. 43.)

[Illustration: Fig. 43--Showing method of cutting through the cornea and
completing the two sagittal sections.]

The two specimens may be kept indefinitely by placing them in a 3 per
cent. formaldehyde solution. It will be well to remove the lens from one
of the specimens, because it will give better opportunity to see the
anatomical relationships. Also, these specimens should be mounted, one
above the other, between two pieces of glass, before placing them in the
receptacle that is to hold them.

Much can be studied in such specimens. Moreover, they present to view
the various parts of the organ of vision in such an impressive way, that
one does not soon forget the wonderful appearance of the construction of
this, Nature’s perfect camera. (Fig. 44.)

[Illustration: Fig. 44--Sagittal section enlarged.]

If another eye is cut into two parts, additional interesting specimens
may be procured; for instance, one showing the presence of the second
coat only, the retina having been torn out. Another good specimen may be
made by removing all of the inner tissues, and leaving only the
sclerotic and cornea. This specimen will show that the first coat is
almost entirely a coat which affords strength and protection to the
parts that lie within.



THE PAPILLA, PUNCTA LACRIMALIA, AND NASAL DUCT


The only way to dissect the lacrimal apparatus, other ocular
accessories, and the extrinsic muscles, is to procure the head of some
animal, preferably a calf’s head, because of its size. Any butcher will
supply one for from forty to sixty cents. Have the lower jaw removed. It
will make a less bulky piece of material to handle.

Close to the inner canthus, on the inner side of each lid, will be found
a little rounded eminence--lacrimal papilla--in the centre of which is a
small opening--punctum lacrimalis. Both may be seen better on the lower
lid, if it is pulled down, and on the upper lid, if it is pulled up.

[Illustration: Fig. 45--Showing only a part of a calf’s head and the
knitting-needles inserted in the puncta. (Page 94.)]

[Illustration: Fig. 46.]

Be supplied with two knitting-needles. Take one, lubricate its full
length with a little vaseline, lard, oil, or any other lubricant. Insert
the needle into the punctum of the lower lid, and push it downward and
forward, aiming to come out in the nose a short distance from its end.
At first it may be a little difficult to get the needle started; if so,
just wiggle the needle, pushing it at the same time as directed, until
the nasal duct is found. Do not remove the needle. To insert the other
needle into the punctum of the upper lid is rather difficult; for that
reason the punctum of the lower lid was chosen, first. Grease the
needle, as was done to the first one, and, with a little patience and
careful manipulation, the canal opening and its course will soon be
found. The needle may then be pushed through until it meets the first
one. (Fig. 45.) From the puncta lacrimalia to the place of meeting of
the two needles, marks the course of the two canaliculi and their
junction before they merge and form the nasal duct. Leave the needles
where they are, and begin cutting away the skin. The needles will then
mark the course of each canal and the duct very plainly. With the small
scissors the canals and the duct may be loosened from the surrounding
tissues. Or, the scalpel may be used to lay open the canals, cutting
along over the top of the needles. (Fig. 46.)

The cilia, palpebræ, palpebral conjunctiva, ocular conjunctiva, and
other superficial ocular accessories may be examined without
dissection.



MEIBOMIAN GLANDS AND DUCTS


An examination of the eyelids will show the openings of the ducts of the
meibomian glands a short distance back of the cilia. Very fine pins or
needles that have been greased may be easily inserted for a short
distance into the ducts, and then a dissection made along the course of
the duct as outlined by the presence of the inserted pins or needles.
Another way to see the glands is to slice through the ducts, with the
scalpel or safety-razor blade, the entire width of either eyelid. This
will separate the glands into two parts and show their length, breadth
and structure.



ENUCLEATION OF THE ORBITAL CONTENTS


The eyes one procures from a butcher or a slaughter house will always
have the extrinsic tissues so badly cut and torn that identification of
the various parts and their relations is impossible. Therefore, it is
best to supply one’s self with the head of an animal, such as a sheep or
a calf, and dissect an eye with all its extrinsic tissues intact. For
this dissection, a hammer and a chisel are necessary in addition to the
tools needed for doing the previous dissections.

[Illustration: Fig. 47--Showing method of making the initial cuts in the
skin. (Page 97.)]

[Illustration: Fig. 48--Part of calf’s head, showing the first cut to be
made in the bones of the orbit. (Page 102.)]

[Illustration: Fig. 49--Showing all the cuts to be made through the
bones of the orbit. (Page 102.)]

Using the left orbit, begin the dissection by making an incision
directly over the supra-orbital ridge, extending from over the inner to
the outer canthus. At the middle of that line, make an incision, and cut
at right angles upward to the top of the head. Next make a cut below the
eye, extending from the outer to the inner canthus. (Fig. 47.) Loosen
the skin from the bone with the scalpel, and lay bare the skull
immediately over the orbit. Fold the flaps of the skin back and fasten
them down to the skull with pins or tacks so they will not interfere
with the work.

[Illustration: Fig. 50--Showing how to pry the cut bone loose. (Page
102.)]

[Illustration: Fig. 51--“In removing orbital contents dissect close to
the bone.”]

[Illustration: Fig. 52--Showing excavated orbit. (Page 105.)]

Using the hammer and the chisel, cut through the roof of the orbit at
the middle of the supra-orbital ridge, and continue upward for about two
and one-half inches. Do not strike hard blows, or the chisel may be
driven through the underlying tissues. Listen for the peculiar sound
that is heard when the bone has been completely penetrated; then remove
the chisel. Continue until the full distance of two and one-half inches
of bone has been separated. (Fig. 48.) Now, begin at the upper end,
and cut through the bone downward to the right for about two inches
toward the outer canthus. A similar line should be cut on the right of
the centre line toward the inner canthus. This will mark out two
irregular, triangular-shaped pieces of bone. (Fig. 49.) Remove the piece
on the right-hand side by prying it off. (Fig. 50.) The left-hand piece
should be pried loose and then carefully cut away with the scalpel, so
that the pulley through which the superior oblique muscle runs its
tendon, will not be injured. In removing the orbital contents, dissect
close to the bone (Fig. 51), so that the periosteum will also be
removed, and form a sort of sac or capsule in which will be contained
the eye with all its extrinsic tissues. If difficulty is experienced in
getting at the posterior parts of the orbit, it will be best to cut away
as much more of the obstructing bone as is necessary. In this way the
“capsule” containing the eye, its six muscles, the lacrimal gland, and
both eyelids, all _in situ_, will be removed. (Fig. 54.) As the orbital
entrance of the optic nerve is neared, care must be exercised not to cut
into this “capsule,” or sever any of the muscles. (Fig. 52 shows the
excavated orbit. Fig. 53 shows an anterior view of the enucleated eye.
Fig. 54 is a side view of the enucleated eye.)

[Illustration: Fig. 53--Anterior view of the enucleated eye.]

[Illustration: Fig. 54--Showing the enucleated eye, its muscles, and its
accessories, all in situ.]



OPHTHALMOSCOPIC EXAMINATION


By practising on an enucleated eye, one may gain considerable ability in
the use of the ophthalmoscope, and also learn to recognize the
blood-vessels and other important parts of the retina. To do this, the
eye to be examined must be very fresh, for only in this condition will
the cornea and lens be sufficiently clear to permit rays of light to
enter the inside of the eye.

However, since the pupil is oblong in shape, and often only a narrow
slit--but several millimetres in diameter--the field presented for
observation is a rather limited one. To increase the pupillary aperture,
take a pin, and force the point through the cornea about three or four
millimetres from the corneo-scleral junction, and at right angles to the
direction of the parallel edges of the pupil. After the pin has been
pushed through until it has reached to within a short distance (one
millimetre) of the edge of the iris, carefully pick up the iris by
raising the pin into a position perpendicular to the cornea, and force
the pin further down into the eye. The pupil will have been enlarged on
one side. Do the same thing on the opposite side, and at each extremity
of the pupil. (Fig. 55.)

[Illustration: Fig. 55--Showing one pin before the iris has been picked
up and pulled back, and three pins after the iris has been picked up and
pulled back.]

[Illustration: Fig. 56--Showing method of gathering up the extrinsic
tissues in order to get rid of the pucker in the cornea.]

The pupil will now have been made square, and so large that no
difficulty will be experienced in reflecting either light into the eye,
or in examining the inside of the eye. Care must be taken not to
lacerate the anterior surface of the lens when the iris is drawn back by
the pins.

Putting the pins into the cornea, and using them as levers with the
point of entrance in the cornea as a fulcrum, will pucker the cornea
considerably, and a good clear fundus cannot be obtained. This is easily
overcome. Simply gather up all the tissues surrounding the eye, force
them backward, and hold them firmly with the fingers of the left hand.
(Fig. 56.) The right hand is then free to handle the skiascope or
ophthalmoscope, so that the interior of the eye may be thoroughly
examined.

Another way to prepare an eye for ophthalmoscopic examination is as
follows: Go to a slaughter house and procure a beef eye from an animal
that has been killed but a few minutes previously. Placing the eye
immediately into an 8 per cent. solution of cocaine and leaving it there
for about an hour will dilate the pupil to such an extent that work with
the ophthalmoscope will be made very easy. This, as indicated, can be
done only with an eye that is very fresh.

[Illustration: Fig. 57--Showing window cut in sclerotic, choroid, and
retina.]

Still another way to see the interior is to cut out a piece of the
sclerotic about the size of a twenty-five-cent piece; then pinch up and
tear out the choroid and the retina under the opening made in the
sclerotic. (Fig. 57.) Hold the eye, the cornea forward, close to a
bright light, and the image of the light will be seen upon the retina.
The closer the light is to the eye, the greater the illumination will be
in the interior of the eye. If the opening or “window” is close enough
to the optic nerve, the optic papilla can be seen easily. And, if care
has been taken to have the opening made midway between the two branches
of the retinal artery, the entire course may be followed. The direction
of the retinal artery can be determined by ophthalmoscopic examination.



THE LACRIMAL DUCTS


To find the lacrimal ducts, cut across the outer and inner canthi of the
enucleated eye, pushing the eye forward and the lids backward. That will
expose the conjunctiva of both eyelids and eye, and also show the
conjunctival fornices. On the upper surface of the palpebral
conjunctiva, and near the outer canthus, will be seen, upon close
inspection, a number of minute openings, usually eight. These are the
openings of the lacrimal ducts. Pins or straw that have been lubricated
with vaseline, may be inserted and pushed into these openings for a
considerable distance, and the course of the ducts then can be traced
easily. (Fig. 58.)

[Illustration: Fig. 58--Showing how pins may be inserted in the lacrimal
ducts.]



THE LACRIMAL GLAND


The lacrimal gland is easily distinguished by its pink appearance. There
are two parts, inferior and superior. The gland lies directly over the
eye and near the outer angle of the orbit. In the enucleated eye, it
will be found to lie near the outer canthus and over the eye. The gland
may be easily dissected out of its position and then examined more
closely. A hand lens will show the racemose construction of the gland.
If the gland is cut in two, the racemose construction may be seen even
better.



THE CAPSULE OF TENON


To dissect the capsule of Tenon, it is necessary to carefully remove the
superficial fat and connective tissue. In text-books and illustrations,
the capsule is usually shown as a definite sac-like membrane of
considerable thickness, with all its parts well defined. The dissector
will soon find that the capsule is not discerned so easily. It will be
found to be the thin, semi-transparent, fibrous membrane that surrounds
each muscle, as well as the “posterior two-thirds of the eye,” and is
continuous anteriorly with the ocular conjunctiva. Portions may be
pinched up and inflated through an inserted blow-pipe. This will help to
merely demonstrate its location and parts. (Fig. 59.)

[Illustration: Fig. 59--Enlarged to show part of the Capsule of Tenon
blown up. (Page 116.)]



THE SUPERIOR OBLIQUE MUSCLE AND ITS PULLEY


After the lacrimal gland has been dissected away, a beginning will have
been made for cutting away the fat and the connective tissue. The first
thing to do then is to locate the superior oblique muscle. Try to keep
track of which part of the eye is the inner side. Having located the
inner side, feel along the top for a little hard eminence. That is the
pulley. Begin to dissect around the pulley, not through it, and then
follow the muscle along to its origin; do not separate the muscle from
its origin. When the superior oblique is completely freed, the action of
the muscle may be readily demonstrated by holding the “ring” or
tendinous pulley with the fingers of one hand, while the muscle is
pulled backward and forward with the other.



THE OTHER EXTRINSIC MUSCLES


With the dissection of Tenon’s capsule and the superior oblique muscle,
the work of isolating the other extrinsic muscles will have begun. This
work needs no directions except a warning to be careful not to injure
the pulley of the superior oblique, and to be careful not to cut away
the inferior oblique. The inferior oblique will be found to be near the
“pulley.” If the dissection is not carried too close to the origin of
the recti muscles, all the muscles may be kept in place.

If the eye has not been previously subjected to the hardening influence
of formaldehyde, it may be put into a 5 per cent. solution, and at the
end of ten or twelve hours the muscles will have become rigid. They can
then be better studied, and may be kept indefinitely. (Fig. 60.)

[Illustration: Fig. 60--Showing the tendinous pulley of the superior
oblique muscle and the extrinsic muscles.]



THE THREE TUNICS OF THE EYE, THE HYALOID AND ITS ATTACHMENTS


This dissection is a rather difficult one to make, and requires
patience.

[Illustration: Fig. 61--Cutting through the iris.]

Prepare an eye by placing it in a 5 per cent. solution of formaldehyde
for about ten days to two weeks. Remove all the outside tissues. Cut
away the cornea, as in the dissection for the choroid or the retina.
Loosen, as far back as possible, the sclerotic from the choroid. Remove
the sclerotic for about 10 mm. back of the equator of the eye. With the
tweezers pick up the pupillary edge of the iris. Using the small pointed
scissors, cut through the iris. (Fig. 61.) Lift either one of the cut
edges of the iris, and, with the sharp edge of the scalpel, gently
scrape the _processus zonuloe_ free from the ciliary processes, cutting
through the ciliary ring as the ciliary processes are detached from the
hyaloid (_processus zonuloe_). (Fig. 62.)

[Illustration: Fig. 62--Scraping the ciliary processes free. Showing,
also, the choroid cut around the ciliary ring.]

Great care must be taken not to thrust the point of the scissors into
the hyaloid, suspensory ligament, or vitreous, else the lens may become
detached.

After the iris with the processes has been removed, pinch up with the
tweezers a fold in the choroid. Make an incision with the fine-pointed
scissors, and begin removing the choroid to within about 5 mm. of the
cut end of the sclerotic. (Fig. 63.) Care must be taken not to penetrate
the underlying retina while making this part of the dissection.

[Illustration: Fig. 63--Cutting away the choroid.]

After part of the choroid has been removed, the specimen will show the
three coats of the eye in layer-like arrangement, the hyaloid and lens.
The lens may now be cut away, if the specimen is preferred without it.
Removing the lens before this time is unwise, because it acts as a
protection to the other tissues while the specimen is being handled
during the dissection.

This specimen will show to the best advantage if it is suspended in a
jar containing a 5 per cent. solution of formaldehyde. Figure 64 shows
the specimen.

[Illustration: Fig. 64--A. Optic nerve. B. Sclerotic. C. Choroid. D.
Retina. E. Hyaloid. F. Lens.]



INDEX


  A

  Accessories, ocular, 95

  Alcohol as a preservative, 34

  Alcohols, method of running through, 58, 59

  Anterior chamber, 50, 51, 86, 90
    half of eye, 49
    half, removing vitreous from, 49
    surface of lens, 55

  Aperture, increasing pupillary, 106, 107, 109

  Aqueous humor, 51

  Arteria centralis retinæ, 43, 49

  Arteries, ciliary, 72
    course of retinal, 111

  Artery of retina, central, 43, 49
    hyaloid, 43


  B

  Beef eyes, 26, 27

  Beginning of dissection of orbital contents, 97

  Benzine, 59

  Blood-vessels of retina, 106

  Blowing through blowpipe, folding retina by, 81, 82

  Blowpipe, folding retina by blowing through, 81, 82
    glass, 35
    using it to force out vitreous, 78-81

  Body, hyaloid, 41

  Boiling crystalline lens, 55, 56

  Books, text, 23, 25, 46, 52


  C

  Canal, hyaloid, 43
    of Petit, 35-37

  Canaliculi, puncta, papilla, and nasal duct, locating, 92-95

  Capsule of lens, 33, 50, 54
    of lens, removing, 59

  Capsule of Tenon, 115
    of Tenon and conjunctiva, 116

  Cedar oil, 60

  Cells of processes, pigment, 49, 50

  Central artery of retina, 43, 49

  Chamber, anterior, 50, 51, 86, 90
    posterior, 50, 51, 86, 90

  Chemicals, 22, 23

  Chisel and hammer, use of, 99-101

  Choroid, 62
    and sclerotic, cutting them away for isolating retina, 83
    emptying, 69, 70
    for dissecting three tunics, removing, 122
    from sclerotic, for dissection of three tunics and hyaloid,
    loosening, 120
    iridescence of, 45
    loosening from corneo-scleral junction, 64, 65
    loosening sclerotic from, 64, 66, 67, 68
    or retina, removing cornea for isolating, 62, 63, 64
    picking up retina and, 30, 31
    preparing eye for isolating, 62
    preserving isolated, 72
    removing, 46
    removing lens from, 69, 70, 71
    scraping sclerotic from, 68
    separating sclerotic from, 27, 29

  Cilia and other superficial accessories, 95

  Ciliaris, corona, 49, 51
    orbicularis, 49, 51
    retinæ, pars, 49

  Ciliary arteries, 72
    nerves, 72
    processes, 27, 33, 49
    processes free from _processus zonuloe_, scraping, 121
    ring, 51
    ring, cutting ciliary, 121

  Ciliary, clarifying lens, 58, 59

  Coats, preparing eye for dissection to show, _in situ_, the three, 120

  Cocaine, 109

  Color of processes, 50

  Concentric layers of lens, 56, 57

  Conjunctiva and Capsule of Tenon, 116

  Conjunctival fornices, 113

  Cornea, epithelium of, 52
    removing it for isolating choroid or retina, 62, 63, 64

  Construction of lacrimal gland, racemose, 114

  Contents, beginning of dissection of orbital, 97-101
    dissecting orbital, 97-105
    emptying eyeball of, 32, 33
    enucleating orbital, 102-104
    material for enucleation of orbital, 97
    preserving of hyaloid, 32, 33, 34, 36

  Cornea, 52
    and sclerotic, 52
    layers of, 52
    smoothing it for ophthalmoscopic examination, 109

  Corneo-scleral junction, loosening choroid from, 64, 65

  Corona ciliaris, 49, 51

  Cortex of lens, 54, 59

  Course of retinal arteries, 111

  Cross section of optic nerve, 48

  Crystalline lens, 33, 49, 53
    lens boiling, 55

  Cutting away sclerotic and choroid for isolating retina, 83
    ciliary ring, 121
    cross section of optic nerve, 48
    eye for sagittal section, 87-89
    eye in half, 38, 39
    iris for dissection of three tunics, 120
    optic nerve longitudinally, 47, 48


  D

  Dehydrating lens, 58, 59

  Demonstration of hyaloid, etc., 34

  Disc, optic, 43

  Dishes, Stender, 21

  Dissected hyaloid, 33

  Dissecting lacrimal gland, 114
    nasal duct, papilla and puncta, 92
    orbital contents, 97-105
    of hyaloid membrane, 25, 33
    of hyaloid, method of preparing for, 26, 27
    of orbital contents, beginning of, 97-101
    three tunics, removing choroid, for, 122

  Dissection, preparing eye for interior, 38
    preparing eye to show the three tunics _in situ_, 120
    of three tunics and hyaloid, loosening choroid from sclerotic for,
    120
    of three tunics, cutting iris, for, 120

  Duct, material for dissecting papilla, puncta, and nasal, 92
    papilla, puncta lacrimalia, and nasal, 92

  Ducts, meibomian gland and, 96
    lacrimal, 112, 113


  E

  Emptying choroid, 69, 70
    eyeball of contents, 32, 33

  Entrance of optic nerve, 43

  Enucleated eye, 104

  Enucleating orbital contents, 102-104

  Enucleation of orbital contents, 97-105
    of orbital contents, material for, 97

  Epithelium of cornea, 52

  Equipment, 17-24

  Examination, ophthalmoscopic, 106
    preparing eye for ophthalmoscopic, 106-110
    smoothing out cornea for ophthalmoscopic, 109

  Excavated posterior half, 46, 47
    sagittal, 90

  Extrinsic muscles, other, 118
    muscles, preserving, 119

  Eye, anterior half of the, 49
    contents, emptying, 32, 33
    cutting it for sagittal section, 87-89
    for dissection of hyaloid, etc., preparing, 26, 27
    in half, cutting, 38, 39
    interior of, 38
    posterior half of the, 40
    preparing for dissecting interior, 38
    preparing it for dissection, to show the three tunics, _in situ_,
    120
    preparing for isolating choroid, 62
    preparing for isolating retina, 74, 75
    preparing for ophthalmoscopic examination of, 106-110
    preparing for sagittal section of, 86
    sagittal section of, 86
    seeing interior of, 110
    vertical section of, 86
    cutting window in, 110

  Eyelids, 95, 105

  Eyes, sheep and beef, 26, 27


  F

  Fibres of lens, 56, 57
    network of vitreous, 41, 42

  Fluid, perichoroidal, 40, 46

  Folding retina by blowing air through blowpipe, 81, 82

  Forcing out vitreous, using blowpipe in, 78-81

  Fornices, conjunctival, 113


  G

  Gland, dissecting lacrimal, 114
    lacrimal, 114
    racemose construction, 114

  Glands and ducts, meibomian, 96

  Glass blowpipe, 35

  Glassware, 21


  H

  Half, anterior, 49
    cutting eye in, 38, 39

  Half, excavated posterior, 46
    posterior, 40
    posterior, excavated, 46
    preparing eye for dissecting interior, 38
    removing vitreous from anterior, 49
    removing vitreous from posterior, 41

  Hammer and chisel, use of, 99-101

  Humor, aqueous, 51
    vitreous, 33

  Hyaloid and attachments, demonstration of, 34
    artery, 43
    body, 41
    canal, 43
    dissected, 33
    membrane, dissection of, 25-33
    membrane with contents and attachments intact, removal of, 25
    preserving contents of, 32, 33, 34, 36
    preserving three tunics and, 123


  I

  Image, retinal, 110

  Increasing pupillary aperture, 106, 107, 109

  Inferior oblique muscle, 119

  Instruments, 21

  Interior of the eye, 38
    of the eye, seeing, 110

  Interior section, preparing the eye for dissecting, 38

  Iridescence of choroid, 45

  Iridescent choroid, 40, 43

  Iris, 49, 51
    and lens, removing, 75, 77
    and processes, removing, 121
    for dissection of three tunics, cutting, 120
    relation between processes and, 51, 52

  Isolated choroid, preserving, 72

  Isolating choroid or retina, removing cornea for, 62-64
    choroid, preparing eye for, 62

  Isolated retina, preserving, 84, 85

  Isolating retina, cutting sclerotic and choroid away for, 83
    retina, preparing eye for, 74, 75


  J

  Junction, loosening choroid from corneo-scleral, 64, 65


  K

  Knitting-needles, use of, 92-95


  L

  Lacrimal ducts, 112, 113
    gland, 114
    gland, dissecting, 114
    gland, racemose construction of, 114

  Lacrimalia, nasal duct, papilla, and puncta, 92

  Laminated structure of lens, 55, 56

  Layers, concentric lens, 56, 57
    of cornea, 52
    separating outer lens, 54

  Lens and iris, removing, 75, 77
    anterior surface of, 55
    boiling of, 55, 56
    capsule, 33, 50, 54
    clarifying, 58, 59
    concentric layers of, 56, 57
    cortex of, 54, 59
    crystalline, 33, 49, 53
    dehydrating, 58, 59
    fibres, 56, 57
    laminated structure of, 55, 56
    nucleus of, 55, 59
    posterior surface of, 55
    preparing the, 53
    preserving the, 57, 58
    removing capsule of, 59
    removing it from choroid, 69-71
    removing the, 51, 53
    separating outer layers of, 54
    staining, 57

  Ligament, suspensory, 33, 37

  Lines, tri-radiate, 54-56

  Locating papilla, puncta, canaliculi, and nasal duct, 92-95

  Longitudinally, cutting optic nerve, 47, 48

  Loosening choroid from corneo-scleral junction, 64, 65
    choroid from sclerotic, 64, 66-68
    choroid from sclerotic, for dissection of the three tunics and
    hyaloid, 120

  Lucidum, tapetum, 45


  M

  Material, 19, 20, 21
    for dissecting nasal duct, papilla, and puncta, 92
    for enucleation of orbital contents, 97

  Meibomian glands and ducts, 96

  Membrane with contents and attachments intact, removal of, 25

  Method of preparing eye for dissection of hyaloid, 26, 27
    of running through the alcohols, 58, 59

  Muscle, superior oblique and its pulley, 117

  Muscles, other extrinsic, 118
    preserving extrinsic, 119


  N

  Nasal duct, canaliculi, puncta, and papilla, locating, 92-95
    canaliculi, puncta, and papilla, 92
    canaliculi, puncta, and papilla, material for dissecting, 92

  Needles and pins, use of, 96, 106, 107, 108, 109, 112, 113
    use of knitting, 92-95

  Nerve, cross section of optic, 48
    entrance of optic, 43
    optic, 47
    optic, cutting it longitudinally, 47, 48

  Nerves, ciliary, 72

  Network of fibres in vitreous, 41, 42

  Nucleus of lens, 55, 59


  O

  Oblique, inferior, 119
    pulley of superior, 117

  Ocular accessories, 95
    conjunctiva and Capsule of Tenon, 116
    conjunctiva and other superficial accessories, 95

  Oil, cedar, 60

  Ophthalmoscope, 109

  Ophthalmoscopic examination, 106
    examination, preparing eye for, 106-110
    examination, smoothing out cornea for, 109

  Optic disc, 43
    nerve, 47
    nerve, cross section of, 48
    nerve, cutting it longitudinally, 47, 48
    nerve, entrance of, 43
    papilla, 111

  Ora serrata, 49

  Orbicularis ciliaris, 49, 51

  Orbital contents, beginning dissection of, 97-101
    contents, dissecting, 97-105
    contents, enucleating, 102-104
    contents, enucleation of, 97
    contents, material for enucleation of, 97


  P

  Palpebræ and other superficial accessories, 95

  Palpebral conjunctiva and other superficial accessories, 95

  Papilla, nasal duct, and puncta lacrimalia, 92
    nasal duct, and puncta lacrimalia, material for dissecting, 92
    optic, 111
    puncta, canaliculi, and nasal, duct, locating, 92-95

  Pars ciliaris retinæ, 49

  Perichoroidal fluid, 40-46

  Petit’s canal, 35-37

  Picking up choroid and retina, 30, 31

  Pigment cells of processes, 49, 50
    of sclerotic, 46
    removal of, 34

  Pinching up sclerotic, 27, 28

  Pins and needles, use of, 96, 106-109, 112, 113

  Pipette, 35

  Posterior chamber, 50, 51, 86, 90
    half excavated, 47
    half of the eye, 40
    half, removing vitreous from, 41
    surface of the lens, 55

  Preparing eye for dissecting interior, 38
    eye for dissecting hyaloid, 26, 27
    eye for dissection to show the three tunics, _in situ_, 120
    eye for isolating choroid, 62
    eye for isolating retina, 74, 75
    eye for ophthalmoscopic examination, 106-110
    eye for sagittal section, 86
    the lens, 53

  Preservative, alcohol as a, 34

  Preserving extrinsic muscles, 119
    hyaloid, contents and attachments, etc., 32-34, 36
    isolated choroid, 72
    isolated retina, 84, 85
    lens, 57, 58
    sagittal sections, 89
    three tunics and hyaloid, 123

  Processes, ciliary, 27, 33, 49
    and iris, removing, 121
    color of, 50
    pigment cells of, 49, 50
    relation between iris and, 51, 52
    zonular, 27, 34

  Processus zonulœ, 34
    zonulœ free from ciliary processes, scraping, 121

  Pulley of superior oblique muscle, 117

  Puncta lacrimalia, nasal duct, and papilla, 92
    lacrimalia, papilla, canaliculi, and nasal duct, locating, 92, 95
    lacrimalia, papilla, canaliculi, and nasal duct, material for
    dissecting, 92

  Pupillary aperture increasing, 106, 107, 109


  R

  Racemose construction of lacrimal gland, 114

  References, 23, 25, 46, 52

  Relation between iris and processes, 51, 52

  Removal of hyaloid membrane with contents and attachments intact, 25
    of pigment from processus zonulœ, 34

  Removing capsule of lens, 59
    choroid, 46
    cornea for isolating choroid or retina, 62-64
    choroid for dissecting three tunics, 122
    iris and lens, 75, 77
    iris and processes, 121
    lens from choroid, 69-71
    lens from anterior half and other parts, 51, 53, 54
    sclerotic to show the three tunics, 120
    the retina from posterior half, 44
    vitreous from anterior half, 49
    vitreous from choroid, 70-72
    vitreous from posterior half, 41

  Retina, 40-74
    blood-vessels of, 106
    central artery of, 43, 49
    cutting away sclerotic and choroid for isolating, 83
    folding it by blowing air through blowpipe, 81, 82
    or choroid, removing cornea for isolating, 62-64
    picking up choroid and, 30, 31
    preparing eye for isolating, 74, 75
    preserving isolated, 84, 85
    removing, 44
    straightening, 42, 43

  Retinæ, pars ciliaris, 49

  Retinal artery, course of, 111
    image, 110
    vessels, 40, 49

  Ring, ciliary, 51
    cutting ciliary, 121
    of superior oblique muscle tendinous, 117

  Running through the alcohols, 58, 59


  S

  Sagittal section, cutting eye for, 87-89
    section, excavated, 90
    section of the eye, 86
    section, preparing eye for, 86
    sections, preserving, 89

  Sclerotic and choroid, cutting them away for isolating retina, 83
    and cornea, 52
    from choroid, for dissection of three tunics and hyaloid,
    loosening, 120
    loosening choroid from, 64, 66-68
    pigment of, 46
    pinching up, 27, 28
    scraping choroid from, 68
    separating choroid from, 27, 29
    to show the three tunics, removing, 120

  Scraping choroid from sclerotic, 68
    processus zonulœ free from ciliary processes, 121

  Section of optic nerve, cross, 48
    cutting eye for sagittal, 87-89
    preparing eye for sagittal, 86
    sagittal, 86
    vertical, 86

  Sections, preparing eye for dissecting interior, 38
    preserving sagittal, 89

  Seeing interior of eye, 110

  Separating choroid from sclerotic, 27, 29, 64-68
    outer layers of the lens, 54

  Serrata, ora, 49

  Sheep eyes, 26, 27

  Skiascope, 109

  Smoothing cornea for ophthalmoscopic examination, 109

  Superior oblique muscle and its pulley, 117

  Staining lens, 57

  Stender dishes, 21

  Straightening retina, 42, 43

  Structure of lens, laminated, 55, 56

  Superior oblique muscle, pulley of, 117

  Surface of anterior of lens, 55
    of posterior of lens, 55

  Suspensory ligament, 55


  T

  Tapetum lucidum, 45

  Tendinous ring of the superior oblique muscle, 117

  Tenon and ocular conjunctiva, Capsule of, 116

  Tenon’s Capsule, 115

  Text-books, 23, 25, 46, 52

  Three tunics, removing choroid, for dissecting, 122

  Tools, 21

  Tri-radiate lines, 54-56

  Tunics, _in situ_, preparing eye for dissection to show the three, 120
    preserving hyaloid and three, 123
    removing the sclerotic, to show the three, 120


  U

  Use of hammer and chisel, 99-101
    of knitting-needles, 92-95

  Using blowpipe in forcing out vitreous, 78-81


  V

  Vena vorticosa, 72

  Vertical section of the eye, 86

  Vessels of retina, blood-, 40, 49, 106

  Vitreous, 33
    network of fibres in, 41, 42
    removing from anterior half, 49
    removing from posterior half, 41
    using blowpipe to force out, 78-81

  Vorticosa, vena, 72


  W

  Window, in eye, cutting, 110


  X

  Xylol, 59


  Z

  Zone of Zinn, 36, 37

  Zonular processes, 27, 34

  Zonulii Zinii, 36, 37

  Zonulœ processus, 34



  Transcriber’s Notes


  Page 127, cutting window in: either in the wrong place alphabetically,
  or it is an error for window, cutting in.

  The (unusual) spellings zonuloe and zonulœ have been retained.


  Changes:

  Footnotes have been moved to the end of the chapter in which they are
  referenced. Illustrations have been moved out of text paragraphs.

  Some obvious minor typographical and punctuation errors have been
  corrected silently.

  In some illustrations the reference letters have been accentuated.

  Page 11, 12: Illustration numbers added.

  Page 127, Gland, racemose construction: page number 114 added.

  Page 130: the entries iris and lens have been moved to their proper
  place; the entry Retinæ, pars ciliaris has been moved to a separate
  line.





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