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THE LIBRARY

OF

THE UNIVERSITY
OF CALIFORNIA

PRESENTED BY

PROF. CHARLES A. KOFOID AND
MRS. PRUDENCE W. KOFOID



THE



ANATOMY AND HISTOLOGY



OF



THE HUMAN EYE.



TH





ANATOMY AND HISTOLOGY



OF



THE HUMAN EYE.



BY



A. METZ, M.D.,



PROFESSOR OF OPHTHALMOLOGY IN CHARITY HOSPITAL MEDICAL COLLEGE,
CLEVELAND, OHIO.




"Yyteia



PHILADELPHIA:

PUBLISHED AT THE

OFFICE OF THE MEDICAL AND SUKGICAL REPORTER.

1868.



Entei-ed, according to Act of Congress, in the year 1868,
BY A. METZ,

In the Clerk's Office of the District Court of the United States for the
Eastern District of Pennsylvania.




CAXTON PRESS OF SHERMAN A CO.



PREFACE.



WHEN, a few years ago, I commenced teaching ophthal-
mology, I seriously felt the want of a text-book on the
Anatomy and Histology of the Human Eye. There
floes not exist, to my knowledge, a treatise on this sub-
ject that includes the results of the labors of the more
recent histologists to be found in ophthalmological jour-
nals and in memoirs on special subjects. It has been
my aim to collect this material into a connected form, and
in such a manner as to adapt it alike to the requirements
of the medical student and of the practising physician.

It affords me pleasure to record my grateful obligations
to Dr. S. W. BUTLER for reading the proofs and overseeing
the publication 4 of the work, and for the beautiful style
in which it is issued, as well as for the obliging disposition
he has always manifested.

I am also under many grateful obligations to Mr. HUGO
SEBALD, engraver, No. 23 South Third Street, Philadel-
phia, for his skill and accuracy in executing the engravings.



M37Q356



VI PREFACE.

In conclusion, I venture to hope that my task has been
performed in a manner satisfactory to the profession, and
that my small book may meet with a friendly reception.

A. METZ.

MASSILLON, OHIO,

June, 1868.



CONTENTS.



PAGE

Anatomical description of the eye, 17

Visual apparatus the eyeball, . . . ' 17

Fibrous tunic, 18

Choroid, .... . . . 32

Corpus ciliare, 40

Musculus ciliaris, ? 40

Iris, . . . ; 45

Ketina, .. . . '. . /..... . . . 55

Crystalline lens, . V . ' 82

Corpus vitreum, . . t . . . , 94

Aqueous humor, ............ 102

Orbit, . . 104

Muscles of the eye, . . . . . . . . . . . 108

" " action of, .'.'.' . . . . . t . .111

Optic nerve, 118

Arteries, . '. . . ' . . 125

Veins, . . . ^. 128

Nerves, ............ 134

Eyelids, '. i ! . . . > r 145

Conjunctiva, 165

Lachrymal gland, 175



ERRATA.

Page 19, top line, read 3 to 4 mm. instead of 3 to 64 mm.

" 48, fifth line from top, read posterior elastic lamina, or membrana Des-

cemeti, instead of anterior elastic lamina.
" 66, sixth line from bottom, read membrana Jacobi instead of membrana

fucoli.

u 62, fourteenth line from top, read first function instead of first functions.
" 89, tenth line from top, read remains instead of remain.
" 107, eleventh line from top, read portion in place of partition ; also, same

page, seventh line from bottom, same correction.
" 108, fourteenth line from top, read Arlt's instead of Alt's.
u 110, ninth line from bottom, read margo instead of marga.



ILLUSTRATIONS.



PAGE

FIG. 1. The eye, . . . . . ' . . . . .16

" " Measurements, . . " . . . . . . .16

2. Vertical section of sclerotica and cornea, ..... 21

" 3. " " human cornea, 25

4. Coarser ramification of corneal nerves of new-born child, . 29
11 6. Veins of the choroid, . . . . . . .36

" 6. Cells of choroidal network, . . . . . . .37

" 7. Cells of black pigment of man, . . . ... 37

8. Ganglion-cells and pale nerve-fibres of choroideal stroma, .. 39

9. Muscular fibres from ciliary muscle, . . . . . 40

" 10. Ciliary region of the human eye, ...... 41

" 11. Non-nucleated fibres forming tendon of ciliary muscle, . . 42

" 12. Muscle of the iris, . 46

" 13. Union of membrane of Descemet with ligamentum iridis pecti-

natum, . . . . . . . .'.'.*'. 48

" 14. Bacillar layer (rods and cones), . . . ... 68

11 15. Rods in the fresh state, . . . . . . ... 59

" 16. Rods hardened in chromic acid, .... . . .60

" 17. Cone from adult human eye seen with central filament, . . 60

" 18. Vertical section of human retina near yellow spot, ... 62

" 19. Granules or nuclei of retina, 63

" 20. Diagram showing connection of retinal layers, ... 65

" 21. Cells of granular layer with filaments, 65

" 22. Connection between the various nervous elements of the retina, 67

" 23. Ganglion-cells from the retina of man, 68

u 24. Cells of connective tissue of human retina, .... 71

" 25. Vitreous metamorphosis of cells of connective tissue of human

retina, . .71

" 26. Fibres of membrana limitans, ....... 71

" 27. Fibre of Mailer, termination on membrana limitans, . . 72

" 28. Transformation of fibres of membrana limitans, . . ' '. 73

" 29. Cellular tissue fibres in internal granular layer of man, . . 75

" 30. Cellular tissue network of retina of whale, . .; . . 76

31. Bloodvessels of the retina, . . . . . . ' . . 80

' 32. u " " . fe. . < -. ' '. 81

.33. Section of capsule of lens of a calf, . v ; '.'.'' 84r



X ILLUSTRATIONS.

PAGE

FIG. 34. Intra-capsular epithelium, central region, .... 85

" 35. Intra-capsular epithelium of marginal region constituting

matrix of lens, . . . . - . . .86

11 36. Cells undergoing transformation, ...... 87

37. Embryonic cells, ......... 87

" 38. Vertical lens-fibres seen from capsule. From a dove's eye, . 87

11 39. Ends of lenticular fibres abutting on lens-capsule, ... 88

" 40. Serrated edges of fibres of lens, ....... 88

" 41. Serrated lenticular fibres from lens of a cod, .... 88

" 42. Termination of lens-fibres against a star-ray, .... 89

" 43. Termination of lens-fibre against central canal, . .89

44. Single fibre, '. ......... 89

" 45. Hexagonal form of lenticular fibres, ...... 90

" 46. Diagram, ........ . . " . 91

" 47. Anterior surface of lens of a child, ...... 92

" 48. Posterior " " " ...... 92

" 49. Anterior and posterior surfaces of lens of adult, ... 93

60. Termination of lenticular' fibres, ..... .93

u 51. Radiary splitting of lamella of lens, ...... 94

" 52, Fibres from zonula of man, ....... 99

" 53. Cells from pars ciliares retinae, ....... 99

54. Thread-like process, ......... 100

" 55. Muscles of the eyeball ......... 109

" 56. Diagram of action of muscles of eye, ..... 112

" 57. The optic nerve, ....... '. . 121

" 58. Transverse section of ischiatic nerve of man, .... 122

" 59. Transverse section of optic nerve, ... . 123

" 60. Longitudinal section of optic nerve and tunics of the eye, . 124

" 61. Arteries and veins of the eye, ....... 126

62. Bloodvessels of the eye (7 figures), ...... 132

" 63. Nerves of the eye, ......... 135

64. Section of the eyelid, ........ 146

" 65. The eyelids, muscles, and ligaments, ...... 148

66. The orbicularis palpebrarum, ....... 162

"67. ....... 163

" 68. posterior surface, ...... 156

" 69. Mode of union between fibres of orbicularis, .... 157

' 70. Bloodvessels of the eyelid, ....... 164

<( 71. Section of annulus conjunctiva of man, ..... 169

" 72. Clavate corpuscles of conjunctiva of bulb, .... 171

" 73. " <{ from ocular conjunctiva, .... 171

74. Lymph follicles from third lid of a hog, . . . .173

75. Part of an acinus gland from conjunctiva of man, . . . 175







LIST OF AUTHORS CONSULTED.



PILZ, PROFESSOR JOSEF:

Lehrbuch der Augenheilkunde. Prag, 1859.

KOLLIKER, A., Professor of Anatomy and Physiology in the Univer-
sity of Wiirzburg:

Microscopical Anatomy. John W. Parker & Son : London,
1860.

RITTER, CARL:

Die Structur der Retina dargestellt nach Untersuchungen

iiber das Walfischauge. Leipzig, 1864.
L'Anatomie normale et pathologique du Cristallin, du Corps

Vitre' et de la Re'tine. Written for Wecker's Etudes

Ophthalmologiques. Tome II. Paris, 1866.
Ueber die Elemente der ausseren Kornerschicht. Archiv f.

Ophthal., viii-ii.
Zur Histologie des Auges. Archiv f. Ophthal., 11-1,

SCHULTZE, MAX:

Observationes de Retinae Structura penitiori. Bonnae, 1859.
Zur Anatomic und Physiologic der Retina. Bonn, 1866.
Ueber den gelben Fleck der Retina, seinen Einfluss auf nor-
males Sehen und auf Farbenblindheit. Bonn, 1866.

NUNNELEY, THOMAS, F.R.C.S.E.:

On the Organs of Vision: their Anatomy and Physiology.
London, 1858.

STELLWAG, PROF. DR. KARL VON CARION:

Lehrbuch der praktischen Augenheilkund. Dritte Auflage.
Wien, 1861.



x ii LIST OF AUTHORS CONSULTED.

BRUCKE, ERNST:

Anatomische Beschreibung des Menschlichen Augapfels.

Berlin, 1847.
KRAUSE, PROF. W.:

L'Anatomie et Physiologic de la Conjonctive. Traite* Theo-
rique et pratique des Maladies des Yeux, par L. Wecker.
Paris, 1861.
LAWRENCE, W., F.R.S. :

A Treatise on the Diseases of the Eye. American Edition,

edited by Isaac Hays, M.D.
ARLT, PROF.:

Ueber den Thranenschlauch. Archiv f. Ophthal., Band i,

Abth. 11.

Sur les Functions et certaines Dispositions Anatomiques Nou-
velles du Muscle Orbiculaire des Paupieres. Compte-
rendu de Congre's d'Ophthalmologie. Paris, 1862.
Ueber den Ringmuskel der Augenlider. Archiv f. Ophthal.,

Band ix, Ab. 1.
Zur Anatomic des Auges. Archiv f. Ophthal., Band iii, Ab. ii.

GrALEZOWSKI, DR.:

Etude Ophthalmoscopique sur les Alterations du Nerf Optique

(chapitre iv). Paris, 1866.
BECKER, DR. F. J. YON:

Untersuchungen iiber den Bau der Linse bei dem Menschen
und den Wirbelthieren. Archiv f. Ophthalmologie, Band
ix, AK 11.
His, W.:

Beitrage zur normalen und pathologischen Histologie der

Cornea. Bale, 1856.
MANZ, W. W., Prof. Agrege a la Faculte* de Fribourg :

Anatomic et Physiologic du Sclerotique et Corne'e. Written

for Wecker's Etudes Ophthalmologiques.
ARNOLD, J.:

Die Bindehaut, der Hornhaut, und der Greisenbogen. Hei-
delberg, 1860.
SCHWEIGGER, DR. C. :

Ueber den Ganglienzelleii und .blassen Nerven der Choroidea.
Archiv f. Ophthal., B. vi, Ab. ii.



LIST OF AUTHORS CONSULTED. Xlii

IWANOFF, DR. A., aus Moskau :

Beitrage zur Nonnalen und Pathologischen Anatomie des
Auges. Archiv f. Ophthal., B. xii, Ab. i.

MULLER, HEINRICH:

Anatomische Beitrage zur Ophthalmologie. Archiv f. Oph-
thal., B. iii, Ab. i.

ZINN, JOHANNIS GOTTFRIED, Professoris Quondam Medici in Uni-
versitate Gcettingensi :

Descriptio Anatomica Oculi Humani. Goettingae, 1780.
ENGELMANN, TH. WILH. :

Ueber die Hornhaut des Auges. Leipzig, 1867.

HEIBERG, HJALMAR, DR., in Christianna :

Zur Anatomie und Physiologic der Zonnula Zinnii. Archiv
f. Ophthal., B. ii, Ab. iii.

GRAEFE, A. VON :

Symptomenlehre der Augenmuskellahmungen. Berlin, 1867.

WELLS, DR. JOHN S.:

Paralytic Affections of the Muscles of the Eye. Ophthal.
Hospital Reports, vol. ii, p. 44.

FICK, PROF. DR. ADOLF:

Lehrbuch der Anatomie und Physiologic der Sinnes Organe.

MULLER, HEINRICH:

Einige Bemerkungen uber die Binnen-Muskeln des Auges.
Archiv f. Ophthal., B. iv, Ab. ii.

LIEBREICH, R.:

Eine Modification der Schieloperation. Archiv f. Ophthal.,
B. xii, Ab. ii.

POPE, DR. BOLLING A., Virginia :

The Nerves and Nerve-Cells of the Choroidea. The Royal Lon-
don Ophthalmic Hospital Reports, vol. iv, part i, 1863.

HULKE, J. W. :

Observations on the Growth of the Crystalline Lens. Oph-
thalmic Hospital Reports, vol. i, p. 182.
A Contribution on the Amphibian and Reptilian Retinae.
Ophthalmic Hospital Reports, vol. iv, part iii.



LIST OF AUTHORS CONSULTED.

GRAEFE, A. VON:

Beitrage der Schiefen Augenmuskeln. Archiv f. Ophthal.,
B. i, Ab. i.

SAMISCH, DR. TH.:

Beitrage zur Normalen und Pathologischen Anatomic des
Auges. Leipzig, 1862.

BONDERS, DR. F. C.:

Ueber die sichtbaren Erscheinungen der Blutbewegung im

Auge. Archiv f. Ophthal., B. i, Ab. ii.

Etude sur les Vaisseaux Yisibles a 1'exterie'ur de 1'ceil. An-
nales d'Oculistique, tome Hi, p. 189.

MOLL, DR. J. A., in Utrecht :

Bemerkungen iiber den Bau der Augenlider des Menschen.
Archiv f. Ophthal., B. iii, Ab. ii.

WITTIG, PROF.:

Studien iiber den blinden Fleck. Archiv f. Ophthal., B. ix,
Ab. iii.

Rosow, DR. R., in Petersburg :

Ueber das Kornige Augenpigment. Archiv, ix-iii.

HENKE, W.:

Die Oefnung und Schliessung der Augenlider und des Thra-

nensackes. Archiv f. Ophthal., iv-ii.
Beleuchtung des neuesten Fortschrittes in der Lehre vom

Mechanismus der Thranenableitung. Archiv f. Ophthal.,

B. viii, Ab. i.

KLEINSCHMIDT, DR. A.:

Ueber die Driisen der Conjunctiva. Archiv f. Ophthal., B.
ix, Ab. iii.

LEBER, DR. TH.:

Anatomische Untersuchungen iiber die Blutgefasse des

Menschlichen Auges. Wien, 1865.
Ueber die Lymphwege der Hornhout. Zehender's Klinische

Monatsblatter fur Augenheilkunde. Januar und Februar

heft, 1866.



i



LIST OF AUTHORS CONSULTED. XV

JAEGER, PROF. VON, JR.:

Ueber die Einstellungen des Dioptrischen Apparates im
Menschlichen Auge. Wien, 1861.

Coccius, DR. A., Prof, der Med. an der Univ. Leipzig :

Ueber des Gewebe und die Entziindung des menslichen Glas-
korpers.



XVI



MEASUREMENTS,



FIG. 1.




LONGITUDINAL SECTION OF THE HUMAN EYE.

A. Lens. B. Aqueous humor. C. Vitreous humor. D. Apex of the ciliary muscle
in the region of the ora serrata. E. Iris. F. Splitting of the membrana Descemetii to
be inserted into the canal of Schlemm in part, and to pass over, in part, to the anterior
surface of the iris. 1. Canal of Schlemm. 2. Outer surface of ciliary muscle. 3. Ciliary
process. 4. Ciliary muscle near its apex. 5. Pupil. 6. Cornea. 7. Anterior capsule
of the lens. 8. Posterior chamber. CP. Petit's canal. CH. Canal of Hanover. (From
Pilz.)



MEASUREMENTS.



1 English inch.



D ;//

1 line.



THE



ANATOMY AND HISTOLOGY



THE HUMAN EYE.



THE human eye is an organo-physical apparatus, which has,
by means of a system of collective media, the property of cast-
ing real images of objects on the retina. The impression of
light thus made on the nerve-membrane is conducted by the
optic nerve-fibres to the brain, wfyere consciousness is enforced.
This wonderful little dioptric organ ranges, anatomically, over
a wide field, containing within itself and its appendages all the
structures composing the human body. As an optical instru-
ment, it is perfect beyond imitation, having the wonderful
property of self-adaptation to long or short distances.

The visual apparatus consists of the eyeball and its accessory
organs, the muscles to move the globe, the lachrymal glands
to moisten it, and the lids to cover and protect it.

The eyeball (bulbus oculi) consists of three tunics of distinct
structure: a fibrous membrane, the sclerotica, with its an-
terior part or window, the cornea (tunica cornea) ; a vascular
and pigment-membrane, the choroid (Briicke's tunica uvea) ; a
nerve-membrane, the retina, on which the luminous impres-
sions are made. Inclosed by these tunics are the refracting
media, a small bi-convex concentrating lens (lens crystallina),

2



18 THE ANATOMY AND HISTOLOGY

inclosed in a transparent membrane, the lens capsule; sur-
rounding this are less refracting media, the aqueous humor,
a thin, watery fluid, which fills the space between the lens and
cornea ; and the vitreous humor (corpus vitrewri) filling the space
between the lens and the retina, consisting of a system of
membranes confining a humid substance, the vitrina ocularis.
The enveloping membrane of this is the hyaloid membrane, and
its continuation forward to the anterior capsule of the lens,
like a corrugated or plaited neck, is the zomda Zinnii. There
are also some transparent membranes, as the outer and inner
epithelial coverings of the cornea, and the covering of the
choroid and retina, the membrana limitans.

The fibrous tunic (tunica fibrosa, sclerotica, cornea). The outer
tunic of the eyeball is a fibrous membrane ; its posterior
opaque section, which includes four-fifths of the membrane,
is the tunica sclerotica ; its anterior, more convex, transparent
section, is called the tunica cornea. According to the more
recent investigations of Henle, Virchow, and others, the fib-
rous membrane consists of condensed cellular tissue ; the
fibrous, or fibrillous structure, seen in investigating the scle-
rotica, vanishes after immersing the eye for some time in
hot water, until the membrane feels hard. The sclerotica is
opaque, white, hard, unyielding, and poor in vessels. It is the
skeleton of the eye ; it serves for the attachment of muscles,
sustains the form of the eye, serves for the transmission of
vessels and nerves to the parts within, envelops the fluids
and protects them. Anteriorly the sclerotica terminates in
the cornea. This change is never abrupt, but the line of de-
marcation is cloudy and semi-transparent. The union seems
to take place by bevelled surfaces, the sclerotica overlapping
the cornea externally, so that the anterior chamber extends
further back than does the cornea on the outer surface. On
its posterior surface, the sclerotica is perforated by the optic
nerve, the sheath of the latter being continuous with the
sclerotica, and similar in structure with it, although much
thinner. The optic nerve entrance is a little to the inner side



OFTHEHUMANEYE. 19

of the eye axis ; according to Hasner, 3 to 64 millimetres. The
optic nerve sheath consists of two layers, an inner fibrous
layer, an outer fibrous layer, with a layer of cellular tissue
between them. Its structure will be considered hereafter, and
is referred to here to aid in the description of the optic nerve
entrance, which is a point possessing considerable pathologi-
ca>Whnportance in connection with glaucomatous conditions.
Bonders says, that of the two layers of the optic nerve sheath,
the outer, with its vessels and nerves, penetrates two-thirds of
the thickness of the sclerotica, whilst the inner layer immedi-
ately proceeds behind the choroid, with which some of its
fibres unite, and turns outward, and is expanded on the inner
surface of the sclerotica. From it, however, a number of elas-
tic elements proceed, and pass between the individual optic
nerve bundles, to form the so-called lamina cribrosa, which is
connected with but a small portion of the choroid. At this
point the optic nerve is only and exclusively surrounded by
the" firm, cellular texture of the sclerotica. The arteria and vena
centralis retinas also pass through the lamina cribrosa, causing
the largest opening in the cribriform lamina, which is some-
times called porus options. Around the optic nerve entrance
the sclerotica is also perforated by the long and short ciliary
arteries, some venous branches, and by the ciliary nerves. In
the region of- the equator bulbi it is perforated by the vasa
vorticosa of the eho&Mlea, and around the corneal border the
arteria and vence ciliares anticce perforate it.

The anterior portion of the sclerotica is covered by the ten-
dons of the recti muscles, but their expansions do not meet so as
to form a continuous membrane, but are only, in a manner, con-
nected by the tunica vaginalis bulbi, or Bonnet's capsule, which
begins at the foramen opticum, envelops the globe loosely,
to a point anterior to the equator, where the recti muscles
perforate it, and it is blended with their sheaths and the ex-
pansion of the tendons, and is firmly attached to the sclerotica
as far forward as the border of the cornea. This latter portion
of the membrane is called Tenon's membrane. This capsule



20 THE ANATOMY AND HISTOLOGY

will be more fully described in another place. The sclerotica is
firmly connected with the choroid in the region of the ciliary
muscle, and at the optic nerve entrance. In the rest of its ex-
tent it is but slightly connected by means of delicate cellular
tissue, the lamina fusea, which contains some nuclei. On
separating the choroid and sclerotica, some of the pigment con-
tained in the lamina fusca is torn loose, and adheres to the
sclerotica. Pilz says that the pigment contained within the
lamina fusca is sometimes increased at the immediate border
of the optic nerve entrance, and causes the dark ring sometimes
seen in using the ophthalmoscope. The sclerotica is thickest
posteriorly, being a little more than \'" . It is thinnest at the
equator, being only \'" to \' h ', and near the corneal border it
is f '" in thickness. In structure, the sclerotica is composed
altogether of bundles of cellular tissue, which cross each other
in longitudinal and transverse layers, the former predominating
posteriorly, and the latter anteriorly. On the other hand, the
cornea is complicated in structure. The cornea 'proper is an
immediate continuation of the sclerotica, also consisting of
condensed cellular tissue, but not arranged in longitudinal and
transverse layers, as in the sclerotica, but the bundles run in
different directions, and its fibres are so firmly interlaced that
it has the appearance of compressed sponge. In boiling, corneal
substance yields chondrin, whilst the sclerotica yields glue. The
cornea is transparent, yet not clear as ci^tal, whilst the scle-
rotica is quite opaque. The cornea is colorless, elastic, and re-
sistant, whilst the sclerotica is white, less elastic, but quite firm.
The cornea may somewhat easily be torn into lamellse, in con-
sequence of its bundles of fibres being parallel, whilst the
structure of the sclerotica does not permit it to be torn into
layers. As S tell wag truly says, the lamellar structure of the
cornea must be asserted, whatever the microscopist may say, as
is seen in the regular splitting of the corneal layers in onyx,
and in interlamellar extravasation of blood. It has been
noticed above, that the cornea and sclerotica are united by
bevelled surfaces, the latter overlapping the former externally.



OF THE HUMAN EYE. 21

This union is so firm that even macerating cannot separate them.
In fact, the cornea proper, or lamellated cornea, and the scle-
rotica, are one continuous membrane. We owe to William
Bowman, of London, a clear and full description of the cornea.
It is an elaborate structure, and consists of five coats or layers,
that can clearly be distinguished, which are, from before back-
ward, the conjunctiva! layer of epithelium, the anterior elastic
lamina, the cornea proper, the posterior elastic lamina, or mem-
brana Descemeti, with its epithelial covering. The cornea proper,
or lamellated cornea, constitutes the main thickness and strength
of the cornea. It is a modification of the white fibrous tis-
sue, immediately continuous with that of the sclerotica. In
the sclerotica the fibres run somewhat regularly, in longitu-
dinal and transverse directions, whilst in the cornea they flatten
out into a membranous form, and follow mostly the main cur-
vatures of the corneal surface, and constitute a series of more
than sixty lamellae, intimately united to one another by very
numerous processes of a similar structure, passing from one
into the other, and making it impossible to trace any one



FIG. 2.



(L




Vertical section of the Sclerotic and Cornea, showing the continuity of their tissue
between the dotted lines, a. Cornea, b. Sclerotic. In the cornea the tubular spaces
are seen cut through, and in the sclerotic the irregular areolae. Cell-nuclei, as at c,
are seen scattered throughout, rendered more plain by acetic acid. Magnified 320
diameters. (From Todd and Bowman.}

lamella over even a small portion of the cornea (Bowman). In
the sclerotica there is a network of the finest fibres, of an



22 THE ANATOMY AND HISTOLOGY

elastic elementary character, leaving at the places where the
original areolse were located, spindle-shaped and stellate spaces,
forming channels, carrying a thin, nutrient plasma. In corneal
substance there is between the bundles of connective tissue, a
less developed and less branching elastic tissue, in the form of
freely anastomosing spindle-shaped and stellate nucleated
cells. These are the " cornea corpuscles." According to Lang-
hans, these corneal bodies are much more numerous near the
corneal border.

The minute structure of the cornea has been the object of
laborious and patient investigation, and yet the published re-
sults of the most recent histologists prove that the work is far
from being perfected. Many points connected with its minute
structure are now the subject of ardent discussions. Engel-
mann ( Ueber die Hornhaut desAuges, Leipzig, 1867) says, that the
cornea proper is composed of the finest fibrillee, which lie close
to each other, and lying between these are numerous cells and
nerves. In the frog these fibrils have a thickness of 0.0001 mm.,
and each one is separated from its neighbor by an immeas-


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