Abraham Metz.

The anatomy and histology of the human eye online

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the sac. (From Pilz.)


The veins of the eyelids and their muscles are collected into
the superior and inferior palpebral veins ; the former pass into
the anterior facial and middle temporal veins, and the latter
into the anterior facial veins. The lymphatic vessels of the
lids proceed to the superficial facial and sub-maxillary lym-
phatic glands.

The nerves of the skin of the eyelids originate from the
nervus trigeminus ; those in the upper lid from the nervus
supra-orbitalis (from the frontal nerve of the first branch) ; and
those of the lower lid from the nervus infra-orbitalis of the
second branch. Besides these, there are passing to the integu-
ment of the lids, palpebral branches from the nervus supra-
trochlearis, a branch of the frontal nerve, from the nervus
infra-trochlearis, a branch of the ramus naso-ciliaris, from the
frontal nerve itself and the nervus lacrymalis, both from the
first branch of the trigeminus.

The conjunctiva (Bindehaut in German), begins at the free
border of the eyelids as the immediate continuation of the
outer integument, covers the posterior surface of the lids,
then passes over to the eyeball to cover the anterior part of
the sclerotica, and the whole of the cornea. It is thus divided
into four divisions : 1, the conjunctiva palpebralis^ which covers
the posterior surface of the lids J'" beyond the orbital border
of the tarsal cartilages ; 2, the superior and inferior reflected
portions, called the superior and inferior palpebral folds ; 3, the
conjunctiva sclerotica; 4, the conjunctiva cornea. This division of
the conjunctiva is not wholly artificial, but is demanded by
morphological conditions.

The conjunctiva is a mucous membrane, and possesses an
epithelium, immediately beneath which is found the most solid
part, the papillary body. By the papillary body is meant the
most solid part of this membrane, not necessarily possessing
papillae. We may then speak of the papillary body of the
ocular conjunctiva, whilst this membrane does not possess any
papillae (Wecker). The mode of union between the papillary
body and the deeper layers, varies according to the different


parts. In the middle of the tarsal cartilages the union is
effected by a very thin, slightly extensible, cellular tissue ; in the
reflected portion (cul-de-sac) the conjunctiva is united to the
eyeball by a cellular tissue with large meshes, which is quite
loose and extensible, so as to permit considerable sliding of the
mucous membrane over the sclerotica. On the sclerotica, the
bundles of connective tissue which spring from the deep parts,
unite themselves with the papillary body, become shorter, and
in consequence of their rigidity resemble the cellular tissue
forming the general covering of the sclerotica. The papillary
body diminishes more and more on the sclerotica up to the
corneal border, with the exception of the raised part, which
follows the superior and inferior borders of this membrane,
and which is named the limbus conjunctiva, and only a very
thin layer pf connective tissue remains, which is lost in the
corneal substance.

The conjunctiva palpebralis is a reddish membrane of a
thickness of 0'".12 to 0'".16, the cellular layer having a thick-
ness of 0'".08 to O'".ll, and* with a lamellated epithelial cover-
ing of O r// .04 in thickness. The cylindrical epithelium prevails
here under the form of a layer of numerous small cells, which
inclose a large nucleus, located near the wall, of a granulated ap-
pearance, due to the presence of excessively fine small molecules.
The deep layer of cells are more elongated, those of the superior
layer being irregularly polygonal. It is here a true mucous
membrane, being connected to the tarsi by a short, firm cellu-
lar tissue, void of fat. On the free, or inner surface, it is only
covered by an epithelium, always moist and slippery, covered
with mucus. It possesses a true textus papillaris, which gives
it the appearance of delicate velvet. This is caused by numer-
ous round projections, composed of bundles of the finest vascular
loops, the termination of nerves and a fine cellular tissue, but
no lymphatics.

These papillae, similar to those of the cuticle, are found only
in this division of the conjunctiva. They are small and cylin-
drical, but become larger and more wart-like toward the cul-


de-sac, where they are found \'" in length. Whilst the
papillae cease with the cul-de-sac, the papillary hody by no
means ceases there. It is formed by a layer of solid cellular
tissue, which is lost little by little, in the sub-conjunct! val
cellular tissue, varying according to the parts of the conjunc-
tiva where it is found. In the middle part of the tarsi the
papillse are small ; toward the posterior border they are more
projecting. In the conjunctiva of the cul-de-sac they have a
large base, but are less prominent. They vary in size according
to the age of the individual, and according to the different
parts of the conjunctiva. They may have a height of O'".l.

The union of the inferior epithelial cells with the papillary
body is made in such a manner that the surface of the latter
is not smooth, and is never covered by a basement-membrane ;
but the tough fibres of the cellular tissue of the papillaries ter-
minate at the surface of the latter by free and slightly projecting
extremities. Even in the conjunctiva bulbi, where the papillae
are wanting, the fibrils of the cellular tissue also terminate
by free extremities, which appear as small teeth attached to
the exterior surface on perpendicular section. There is no
direct union between the fibrils of the cellular tissue with the
most inferior epithelial cells.

The two things to be observed as peculiar to this division of
the conjunctiva are: 1. Its close adherence to the subjacent
parts, being so closely tied down to the tarsi as to possess no
wrinkles nor folds ; 2. There are wanting in this region of the
conjunctiva the glands which are present elsewhere in every
mucous membrane.

The second division of the conjunctiva, the cul-de-sac or the
palpebral folds, is different from the palpebral portion in being
connected with the parts beneath it by a loose connective tissue,
by the formation of folds, and by the presence of glands, which
will be described hereafter. The upper reflected fold is not
easily seen, but by everting the lid, and the eye being directed
downward, and the border of the everted lid pressed in the
direction of the orbit, a view may be obtained of it. Toward


the outer angle of the eye the fold is wanting, but instead
there is behind the outer commissure or lid-band somewhat of
an excavation. At the inner angle of the eye this reflected
portion forms a duplicature of the conjuiictira, called plica
semiluTlaris, which contains a minute plate of cartilage (the
rudiment of the third lid of animals) ; its papillae are small,
velvety, and have but little prominence.

It has resting on it a little elevated body, the caruncula lacry-
malis, which is an aggregation of sebaceous glancls, similar to
the Meibomian glands, and hair-follicles. These glands are
surrounded by fat-cells, and have a size of \'" to \"' '. The
hairs are very short and quite fine, and have a length of V" to
6'", and 0/"006 to 0'".01 in thickness. The plica semilunaris
rests on the inner lid-band (tendo-ocidi), and supports the carun-
cula lacrymalis. This fact was alluded to in the description of
the iM-band.

The third division of the conjunctiva, the conjunctiva sclero-
tica, covers the sclerotica on the lower and' inner segment of
the globe 3 //r , and on the upper and outer segment from 5J'"
to 6'". On the inner and outer sides of the ball it passes 2'"
back of the insertion of the muscles, and on the upper and
lower surfaces about 1 J'". It is more tender and thin than the
above described divisions ; is somewhat transparent, so that the
sclerotica and Tenon's membrane are seen through it. It is
rich in elastic fibres, and its submucous connective tissue is
abundant, with more or less fat-cells, and is attached to the
membrane of Tenon. It is loose and yielding, and permits
considerable sliding between the conjunctiva and globe. It
lacks papillae and glands, but has a fully developed epithelium.
At the border of the cornea is a ring-formed ridge, "' to V"
broad, which is especially visible in aged persons (annulus con-
junctive^ limbus conjunctivas). It infringes on the cornea more
above and below than at the sides, and forms the boundary
between the third and the fourth divisions of the conjunctiva.

According to "W. Krause it is constituted by the continuation
of the fibre-bundles of the conjunct ival cellular tissue, which



passes on the superior and inferior borders of the cornea. Be-
tween these irregularly interlaced bundles, which form slight
band-like projections, are longitudinal furrows, which are com-
pletely filled by a thick layer of pavement-epithelium. On
their transverse diameters, these bands have a papillary aspect,
as seen in Fig. 71, and the nerve-fibres end in their cellular
tissue by terminal corpuscles. On the contrary, the nerve-
fibres destined for the cornea lose their double contour and
become very pale on having passed on this membrane. They

FIG. 71.

Vertical section of the annulus conjunctiva of man at the superior surface of the
cornea. Magnified 250 diameters. The tract of the cellular tissue of the conjunctiva
(discovered by M. Manz), which is prolonged on the corneal border, appears under the
form of papillae (a), between which is found a thick layer of stratified pavement-epithe-
lium (b, b). (From Kransr,.)

also interlace, but do not form terminal loops. Most likely
the isolated fibres always terminate by a club-shaped enlarge-
ment, which has no special envelopment. The nerves of the
cornea are exclusively beneath the epithelial layer of the ante-
rior corneal surface.

The fourth division of the conjunctiva (the conjunctiva cornea)
has been described in connection with the cornea.

The description of the arteries and veins of the conjunctiva
has been given in connection with the vascular system of the
eye, to which part of this treatise the reader is referred.

The nerves are numerous, and are branches of the palpe-


bral rami of the sub-trochlearis, frontal and lachrymal, which
all proceed from the first branch of the fifth pair. The con-
junctiva of the hulh receives its nerves from the sub-trochlear
nerve. The mode in which the nerves terminate in the con-
junctiva is peculiar (W. Krause). The branches which emanate
from the sub-conjunctival cellular tissue, by successive division,
their anastomoses, and their exchange of fibres, represent a
rich nervous plexus, of which each ramuscule contains a num-
ber of smaller and smaller fibres, whilst the intermediate
meshes become more narrow as the nerves become more
superficial. The nervous fibrils of double contour often divide
dichomatously ; they never end in loops, are not lost free in
the tissue, but, on the contrary, they always end by small
particular organs, which Krause has named terminal davate
corpuscles (corpuscules claviformes, Endkolben, corpusculce ner-
vorium terminalia bulboidea). These terminal clavate corpuscles
are composed of an envelope of fine cellular tissue, with granular
contents of soft consistence, semi-liquid, and in each of these
corpuscles terminate one or two nerve-fibres of double contour,
which often make several circumvolutions, and represent a large
knot, as seen in Fig. 72. In the interior of these clavate cor-
puscles the nervous branches divide again into two or three
very fine branches, short and pale, which run a somewhat tor-
tuous course, and terminate in a slight club-shaped enlargement,
as seen in Fig. 73. " The clavate corpuscles are always situated
superficially beneath the epithelial layer of the conjunctiva ;
their diameter is 0.03mm. to 0.07mm., the medium being
0.04mm. When they are elliptical their length is double that
of their breadth. Krause has named the pale nervous fibres
which are in the interior of these terminal corpuscles, terminal
fibres. They have a diameter of 0.0028mm. The terminal
clavate corpuscles are also found in the lips, the tongue, and
palate in the human being.

In the ocular conjunctiva of man there are found, for each
eye, from 76 to 82 terminal clavate corpuscles ; generally one
may be counted to the square millimetre. In the cul-de-sac



and the tarsal portion they are much more thinly distributed.
In this last part they are subjacent to the papillae.

FIG. 72.

Clavate corpuscles of the conjunctiva
of the bulb. Magnified 350 diameters.
It is taken from th conjunctiva of man,
three hours after death. The nerve-fibres
of double contour (c) proceed side by
side, and, after having formed a knot,
interlace several times before entering
into the large corpuscle, a, b, b. Terminal

FIG. 73.

Clavate corpuscles of man eight hours
after death, from the ocular conjunctiva.
Enlarged 350 times, a. Tortuous terminal
fibre, b. Termination of this fibre in form
of club. c. Fine granular substance of
the corpuscle, d. Nuclei of the cellular
envelope. (From Krause.)

The lymphatic vessels are quite numerous in the conjunctiva
of the bulb, and less numerous in other parts of the conjunctiva.
Krause says that in order to discover them under the micro-
scope, it is necessary to make colored injections.

At the cornea! border the lymphatic vessels form a delicate


network, with uneven meshes, formed of very fine ramifications,
0.004 mm. in diameter. Where the ramifications anastomose are
found enlargements ; toward the cornea this network terminates
mostly by slightly curved arches. The part of the lymphatic
vessels which extends over the breadth of a millimetre is called
the lymphatic circle.

At its periphery is found a lymphatic vessel of a larger
calibre, and which seems to limit it, and the corneal border is
thus surrounded by a somewhat regular circle. To this vas-
cular circle a large number of lymphatics are again connected,
which proceed to the centre of the cornea in a radiary direction.
These vessels have a diameter of 0.94 mm. ; they anastomose
among themselves by transverse branches of a diameter of
0.018 mm. to 0.054 mm.

At the distance of 4 to 5 millimetres from the corneal
border the vessels which had to that point a radiary direction,
take another course ; in the upper lid they run parallel to the
border of the cornea, and inward and outward, acquire con-
siderable dimensions, and open in the true lymphatic branches,
which only are armed with valves. These are directed toward
the external and internal angles of the eye, and end in the
superficial sub-maxillary lymphatic ganglia. Throughout, the
capillary bloodvessels are nearer to the conjunctival surface
than are the lymphatic vessels.

The conjunctiva contains lymphatic glands. These are folli-
cles, globular or elongated, and completely shut, and are situated
immediately beneath the mucous surface. They are composed
of an envelope of solid cellular tissue, and of a fine capillary
network, which expands in the globular cavity ; between the
meshes of this network is suspended a second network of cel-
lular tissue, very solid, but finer than the first. The spaces
that the two kinds of network leave among them are filled
with a little liquid, and a great number of pale cells, round,
with only one nucleus, which are perfectly identical with the
lymph-corpuscles. The lymph-follicles generally have a diam-
ter of /r/ .2 ; in the cul-de-sac they are scattered, and are found,


as well in the superior as in the inferior lids, but exist exclu-
sively in their internal half. They are in all respects similar
to the solitary glands of the intestinal canal, which have no
excretory orifice, and like them, are in connection by their
situation with the lymphatic vessels.

FIG. 74.

Lymph-follicles, from the third lid of a hog. Magnified 120 diameters. (From Krause.)

They are quite variable in number, and sometimes cannot be
discovered at all. Bruch first attracted attention to these fol-
licles. Bendz and Stromeyer considered them pathological
products, and that they are the seat of trachomatous diseases.
W. Krause denies this, and says they are wholly physiological
in their character, and that the granulations of military oph-
thalmy have a quite different structure. W. Krause says that
the results of recent injections leave no doubt as to the lymphatic
character of these follicles. A fine lymphatic network com-
pletely envelops the follicles.

The tissue which surrounds the follicles is, in fact, so rich in
lymphatics, that, when examined without having injected the
vessels, it seems to be completely filled with lymphatic corpuscles,
whilst really these elements are contained within these vascular
walls. W. Krause names it lymphatic infiltration ; His names
it adenoid tissue. There are also numerous lymphatic vessels
in the palpebral conjunctiva, according to Krause. Frey has
also discovered that between and on the follicles there is ex-
panded a rich network of lymph vessels. It can hardly be
doubted that these follicles have a connection with the system
of lymph vessels.


The acinus glands (acinus glandulosus) of the conjunctiva
were first ^discovered by C. Krause, and described by him as
glandules aggregates muciformes. On more thorough investigation
of their character by W. Krause it was ascertained that these
glands are constantly found in the human conjunctiva, and
that they are in their anatomical characteristics entirely similar
to the lachrymal gland. They are found in the cul-de-sac, or
reflected portion of the conjunctiva, between the tarsal carti-
lages and the eyeball. In the upper cul-de-sac there are 42 of
them, and in the lower cul-de-sac from 2 to 6. They are
located irregularly in the texture of the conjunctiva or beneath
it, and are most numerous in the reflected fold. Near the outer
angle of the eye there are sometimes in the upper cul-de-sac 8
to 12 in a row. In size they are very different (Fig. 75).
They measure from J'" to J'" to T V", and only become visible
under the microscope. Their size seems to be dependent on
their number, the individual glands being smaller the more
numerous they are in the eye.

The form of these glands in the conjunctiva is ordinarily
round or oval. Sometimes two glands are united so as to have
one outlet. Each gland has an oblique outlet, opening on the
conjunctiva. They consist of longitudinal fibres of connec-
tive tissue, between which. are embedded elongated oval nu-
clei. Their breadth is ? V"~ to ' S V"> and V" to I'" in length.
The excretory duct divides itself into smaller branches. The
acini lie in the expansions of the wall of this canal. Each
acinus is surrounded by a structureless membrana propria,
7 Jo'" in thickness. The acini themselves have a diameter
of T V", and can be seen only under .the microscope. The
contents of the vesicles consist of cells, free nuclei, and fat-
globules. The cells inclosed within the acini are flat, irregular
polygonal in form, in size yi^"' to T |^ //r , and contain nuclei of
g ^ to 4^o /r/ m s i ze - The neighboring arteries send but few
branches to those glands. These form a large-meshed net-
work. Kleinschmidt could never trace any nervous filaments
to the acini. W. Krause once saw a nervous fibril pass be-



tween two acini, and traced its course for some distance. In
another instance he saw a nervous branch enter a large gland,
which divided into 8 fibrillse, which he traced to the middle
of the acinus, but failed to discover its ultimate distribution.
As far as is now known, the lymphatic glands and the acinus
glands compose all the glands of the human conjunctiva. The
sweat glands and glands of Manz (see Kleinschmidt, Archiv,
ix-iii) have not, with any degree of certainty, been discovered
in the human conjunctiva.

FIG. 75.

Pnrt of an acinus gland from the conjunctiva of man, magnified 250 diameters. It
shows the contents of the acini, and the structure of the outlet of the gland, showing
cellular tissue with nuclei, a, a, a, a, a. Drops of fat. (From Kleinschmidt.)

Glandula Lacrymalis.

The lachrymal gland is lodged in a depression at the outer
angle of the orbit, on the inner side of the external angular


process of the frontal bone. It consists of an upper and larger
portion, and a lower and smaller portion. The former (some-
times named glandula innominata Galeni) is lodged in the fossa
of the zygomatic process of the frontal bone, under the roof of
the orbit, has a yellow-red color ; in its long diameter it is flat,
upward and outward convex, downward and inward concave.
Its length is 9'", breadth 5"', and 2J'" in thickness, and weighs
10 to 12 grains, and has a volume of 57 cubic lines. The second,
lower portion (glandulce congregate Monroi) lies below the upper
portion, and extends beneath the ligamentum palpebrale exter-
num, is 4 to 5'" long, 3J'" broad, V" thick, and weighs 3f grains,
with a volume of 19 cubic lines. In structure, they both con-
sist of roundish gland-vesicles, which are somewhat firmly con-
nected by a short cellular tissue, and are enveloped by a common
connective tissue membrane. The individual glandular bodies
contain the vesicular beginnings of the smallest excretory
ducts, which unite into large branches, and are in number
from 8 to 10, and penetrate the conjunctiva in the reflected
portion, toward the outer part of the upper eyelid. Their con-
tents are diffused over the anterior part of the globe. It is be-
lieved by some (Sappey) that the lower lobe sends an excretory
duct to communicate with that of the upper lobe. Hyrtl says
that the lower, outer, has several excretory ducts that open
into the lower reflexion of the conjunctiva, near the outer eye-
angle, so as to supply the lower lid also with the lachrymal

The excretory ducts, from 8 to 10 in number, consist of
structureless membranes, which extend from the conjunctiva
to the structureless gland- vesicles. Their inner surface is lined
by cylindrical epithelium, whilst on their outer surface they
are surrounded with connective tissue, with some elongated
nuclei. Muscular fibres are wanting, but elastic fibres are nu-
merous, which likely aid in the removal of tears.

The lachrymal gland derives its blood from the arteria lac-
rymalis (Fig. 61), a branch of the arteria ophthalmica. The
venous blood is poured into the ophthalmic vein, from the


lachrymal vein (7, Fig. 61). The nervous supply is wholly from
the first hranch of the trigeminus, which seems under the mi-
croscope to be richly supplied with fine sympathetic fibres.
This nerve presides over the secretion of tears, which is won-
derfully increased by mechanical irritation, or certain emo-
tional impressions. Under ordinary conditions, there is but
little secretion of tears, the greater amount of secretion being
the product of the conjunctiva. The lachrymal gland and the
conjunctiva are the secretory organs of the lachrymal appar-
atus. The tears are pure water, with some table-salt and albu-
men mixed with it, and by analysis, contain, according to M.
Frerichs (Krause):

Water, 99.06

Solid constituents, 0.94


The solid parts are :,

Epithelium, 0.14

Albumen, 0.08

Chloride of sodium, "|

Alkaline phosphates, 2

Earthy phosphates,

Fat and extractive matter, J


The acinus glands likely secrete a product altogether similar
to that secreted by the lachrymal gland.

The derivative parts of the lachrymal apparatus remain to be
described. They are the lachrymal canals, the lachrymal sac,
and the nasal duct.

The derivative lachrymal organs begin on a slight elevation,
or papilla, the papilla lacrymalis, situated on the posterior edge
of the free border of the eyelids, at the outer extremity of the
lacus lacrymalis. At the apex of each papilla, or tubercle, is a
small orifice, the punctum lacrymale, which are the commence-
ment of the lachrymal canals (canaliculi lacrymales). The pa-
pilla are composed of contractile cellular tissue, closely felted,



and are riot contracted nor dilated, neither spontaneously nor

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