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pass through the fissura orbitalis superior, with the exception
of the optic nerve. Another nerve, the nervus subcutaneus
malce, which springs from the nervus infra-orbitalis, a branch
from the second ram us of the trigeminus, passes through the
fissura spheno-maxillaris sea orbitalis inferior into the orbit.
After a short course, during w^hich it forms anastomoses with
the nervus lacrymalis, it passes out again through the foramen
zygomaticum orbitale. The main branch, the nervus infra-orbi-
talis, passes through the canalis infra-orbitalis^ and ends in the
integument as the rami palpebralis, nasales laterales, and labialis
superiores.

As regards the deep origin of these nerves : The nervus ocu-
lo-motorius proceeds from the inner side of the pedunculi cerebri,
where some of its fibres are connected with the substantia
nigra and the tegumentum, the fibres passing backward and
inward to the floor of the aquseductus Sylvii, where they are
lost in the gray substance.

The nervus trochlearis and the nervus abducens have an origin
like the oculo-motorius and the motor roots and muscular
branches of the spinal nerves. The nervus trochlearis origi-
nates from the laqueus, immediately back of the tubercula
quadrigemina, and immediately through these, from the an-
terior column of the spinal cord, which latter receives its
fibres from the pyramid of the elongated marrow at the
posterior border of the pons Yarolii.

Although the nervus oculo-motorius, the nervus trochlearis,



140 THE ANATOMY AND HISTOLOGY

and the nervus abducens, are some distance apart after their
passage from the brain, they yet have a common direction in
their course from their origin at the posterior part of the base
of the brain to the fissura orbitalis superior of the orbit.

The nervus oculo-motorius passes into the orbit uppermost,
and immediately beside the processus clinoideus posterior of
its side, the nervus abducens undermost on the upper side of
the clivus, and the nervus trochlearis on the outermost side.
In their further course they are surrounded by the sinus caver-
nosus on the outer side of the carotis; the nervus oculo-moto-
rius and the nervus abducens, being immediately in contact
with the carotis, the former further inward and the latter
beneath it, whilst the nervus trochlearis lies to the outer side
of the oculo-motorius, which separates it from the carotis.

Still further forward the trochlearis remains on the outer
side of the nervus oculo-motorius, and only at the tendinous
ring of the orbit does it turn more upward. In this whole
extent of its course it lies on the outer side of the first branch
of the trigeminus, which comes from the ganglion gasseri,
which connects itself with the fasciculi of the three motor
nerves of the eye, and thus assumes an outer position to the
nervus oculo-motorius and the nervus abducens, and an inner
position to the nervus trochlearis. During their position in
contact with the carotis, the nervus oculo-motorius and the
nervus abducens form connections with the plexus caroticus.
This connection with the nervus oculo-motorius signifies that
the sympathetic root of the ganglion ciliare passes to this
nerve, to proceed with it into the orbit, whilst the importance
of the connection with the nervus abducens, which at this
point is enlarged like a plexus, is not yet known, but which is
likely a giving off of fibres to the sympathicus.

As regards the origin of the nervus trigeminus, and more
particularly of the ramus ophthalmicus, Budge supposes that
the motor fibres going to the pupil originate above the second
cervical nerve, and the others pass in the corporibus restiformi-
bus and the loca coerulea. The trigeminus does not only form



OF THE HUMAN EYE. 141

an anastomosis with the oculo-motorius, hut also with the ab-
ducens, and sometimes with the trochlearis. Through these
connections, doubtless, are the nerves supplying the ocular
muscles furnished with sensitive fibres.

The fibres of that part of the nervus sympathicus which
proceed to the nervi oculo-motorius, abducens, and trochlearis,
as well as those given off to the vascular nerves supplying the
arteria ophthalmica, which make up the plexus ophthalmicus,
come from the plexus caroticus internus, and from that part
of the plexus cavernosus within the sinus cavernosus, and from
the upper cervical ganglion of the sympathicus. From this
plexus some fine connecting fibres proceed, and connect with
the ganglion gasseri, the portio major of the nervus trigeminus,
and to the ramus 1, nervi trigemini. The origin of those fibres
of the sympathicus which go to the iris and the dilatator pupillce,
Budge found in the cervical portion. They come on the one
side from the spinal marrow and medulla oblongata through
the rami communicantes of the second and first thoracic of the
eighth and seventh cervical nerves, from a lower centre, of
which the essential part is the middle column of the spinal
cord ; on the other side, from a connecting twig below the
ganglion cervicale supremum, which connects the latter with
the nervus hypoglossus, from an upper centre, located near the
lower.

Budge names the part of the sympathicus which proceeds
only to the iris, the iris sympathicus, and says that it contains
both sensory and motor fibres, the former running from the
iris to the spinal cord, and the latter from the spinal cord to
the iris. Hitherto it has not been demonstrated that there is
any relation between the ganglia through which the iris sym-
pathicus passes and the nerve fibres which are destined to
dilate the pupil.

We are as yet unable to determine with certainty what spe-
cial portions of the brain preside over the function of sight. In
the cerebral hemispheres, which are the seat of consciousness,
thought, and reason, the impressions made on the retinae and



142 THE ANATOMY AND HISTOLOGY

on the fifth nerve are elaborated, and decisions made on the
form, size and character of objects.

When the brain is diseased or injured, the vision may be
perfect, but the power to comprehend that which is seen, to
connect things, and to form conclusions, is destroyed. The
impressions of light are felt, the eyes move, the fifth nerve
remains impressible to mechanical irritation, but the power of
collecting the impressions is gone, the eyes no longer move
under the influence of a will guided by intelligence, but roll
around unconsciously.

The optic nerve-fibres run into the anterior tuber cula quadri-
gemina, or nates, and these latter are the seat of the luminous
perceptions. When these tubercles are removed in animals,
blindness ensues, the pupils dilate, and remain motionless.
The removal of one of these eminences causes blindness of the
eye on the opposite side : the pupil will dilate, and act only in
sympathy when the other eye is impressed by light. The
retina, however, is the organ on which the luminous impres-
sions are made, and the office of the tubercula quadrigemina
is likely purely psychical. The optic nerve-fibres do not ex_
clusively originate in the nates, but they also extend into the
gray mass of the thalami optici, which belongs to that part of
the brain presiding over voluntary motion, in which are also
lost the radical fibres of the corpora restiformia, which, as has
been explained, have an intimate union with the ramus oph-
thalmicus of the nervus trigemini.

In this manner there is established an intimate union be-
tween the impressions of touch and the voluntary movements
with the functions of the retina.

In the intimate interlacement of the fibres of the trigeminus
with the optic fibres in the brain are brought about the power
to define that which is seen, to form conceptions of the dimen-
sions of space, etc. The perception of the condition of the
accommodation, the power to distinguish it from the impres-
sions made by the contraction of the muscles, is assisted by
the nervus dliaris longus, which is double, and which is mostly



OF THE HtMAN EYE. 143

quite separate from the rest of the ciliary nerves, given off from
the ganglion ciliare, and proceeds to the tensor choroidea.

The trigeminus acts through the sensation, to indicate the
degree of retinal activity, and acts as a regulator to the quan-
tity and intensity of light the latter can bear, and interferes to
protect it by contracting the iris. The trigeminus further in-
fluences the nervus fadalis tyy causing the lids to contract
when the light is too bright.

The trigeminus is also the active agency that presides over
the nutrition of the eyeball, especially of the cornea. It keeps
it transparent. It is well known that when the fifth nerve is
injured the cornea becomes opaque, the conjunctiva is con-
gested, the ball becomes anaesthetic, the cornea sloughs, and
the eye is lost.

The motive power of the eye has its seat in the pons Varolii
and the medulla oblong ata. It is well known that injuries of
those parts cause complete immobility of the eye with dilata-
tion of the pupil.

The above description of the nerves of the eye, which has
been, to a great extent, translated from Pilz, aims to present
to the reader a view of their relations and connections with
each other. It will aid the student in acquiring a better
knowledge of the separate nerves and their ramifications, to
give a brief resume.

The nervus oculo-motorius is connected with the part of the
cerebrum corresponding with the anterior cords of the spinal
column. They appear at each edge of the crus cerebri, ante-
rior to the pons Varolii, and posterior to the corpora albicantia,
some of its fibres extending into the 1 locus niger of the crura,
and others to the corpora q uadrigemina. It receives a filament
from the sympathetic in the cavernous sinus, and divides
into an upper and a lower branch, which enter the orbit
between the two heads of the abductor muscle. The smaller
or upper branch is distributed on the ocular surface of the
rectus superior and the levator palpebrse muscles. It anas-
tomoses by its twigs with the nasal nerve.

The lower and larger branch is distributed on the ocular



144 THE ANATOMY AND HISTOLOGY

surfaces of the rectus interims, the rectus inferior, and the
obliquus inferior. It communicates with the lenticular gan-
glion by a short thick branch.

The fourth pair of nerves, the nervus trochlearis, is the small-
est of the cranial nerves. It is a motor nerve, and is distributed

*

on the ocular surface of the obliquus superior.

The ophthalmic division of the fifth pair of nerves (trigemi-
nus) has its central connection with the lateral part of the me-
dulla oblongata, continuous with the floor of the fourth ven-
tricle, being a nerve of sensation. It is the uppermost and
smallest division of the casseroid ganglion. In the cavernous
sinus it receives twigs from the sympathetic plexus, and before
entering the orbit it divides into the frontal, the lachrymal,
and the nasal nerves.

The frontal, the largest of the three branches, divides into
an outer larger branch, the supra-orbital, and an inner smaller,
the supra-trochlear, which (latter) passes out of the orbit above
the pulley of the inferior oblique muscle, where it subdivides
into numerous branches for the muscles and integuments. The
supra-orbital escapes at the foramen of the same name, to the
brows and forehead.

The nasal subdivides into the proper nasal, and the infra-
trochlear. It gives off a branch to the lenticular ganglion.
The nasal branch is distributed to the Schneiderian membrane
of the nose. The infra-trochlear supplies the lachrymal sac,
conjunctiva, eyelids, and neighboring skin with sensation.

The lachrymal branch enters the lachrymal gland, and sends
filaments into the conjunctiva and lids.

The sixth pair of nerves, the nervus abducens, is a motor
nerve, having its origin from the pyramidal body of the
medulla oblongata, close to the pons Yarolii, and is distributed
exclusively to the ocular surface of the rectus externus.

The lenticular ganglion, belonging to the ganglionic system,
or organic system of nerves, is about the size of a pin's head,
located at the back part of the orbit, and after receiving twigs
from the nasal and the motor oculi nerves, sends off from 14



\

OF THE HUMAN EYE. 145

to 18 posterior ciliary nerves to enter the sclerotica about two
lines from the entrance of the optic nerve.

It will he perceived from the distribution of the nerves that
the cerebro-spinal and the sympathetic systems of nerves are
intermixed in the eye. That the iris and the ciliary body are
supplied with both is evident. Graefe says that the force

/

which presides over active accommodation is derived from the
cerebro-spinal system ; the other, which holds under its control
the circular fibres of the ciliary muscle, is derived from the
ganglionic system. On this last opium and belladonna act
with opposite effects, the former paralyzes, which permits the
pupil to contract, whilst the belladonna excites those nerves,
and dilates the pupil, by contracting the radiary muscular
fibres.

The Eyelids.

The eyelids are two movable curtains, being continuous
with the integument. They are connected with the border of
the orbit and the globe of the eye by processes of fibrous
membrane or fascia. These curtains or folds are composed
externally of integument, on their inner surface of mucous
membrane, and inclosed between these are the tarsal carti-
lages, glands,- hair-bulbs, muscles, bloodvessels, and nerves.
They close the cavity into the orbit, and lie over the anterior
convexity of the globe, being kept in close apposition by the
action of the muscles, and atmospheric pressure. The free bor-
der of the lid measures about l //r , and it has an outer sharp
border, on which are found the cilice or eyelashes, and a posterior
rounded border, on which are the openings of the ducts for
the Meibomian glands (<?, Fig. 64).

The elliptical space between the upper and lower lids is the
palpebral fissure (fissura palpebralis), at each end of which is
the union between the upper and lower lids, forming the inner
and outer angles of the eye, or canthi, of which the outer is
more acute than the inner, but the latter is prolonged inward
toward the nose for a short distance. According to the obser-

10



146



THE ANATOMY AND HISTOLOGY



vations of Arlt, on frozen eyes, the free borders of the lids, when
the eyes are closed, are in complete contact, on their inner
border as well as on their outer, and the triangular space



Fm. 64.




a. Free border of the eyelid, b. Outer lip of palpebral border, c. Inner lip of the
palpebral border, and also the mouth of the duct of a Meibotnian gland, d. Tarsal carti-
lage, e. Fascia-like membrane between the cartilage and the orbital border, f. Meibo-
mian glands, g. Inner portion of orbicularis (musculus tarsalis). h. Fibre-bundles of
the orbicular muscle, i. Cellular tissue beneath the orbicular muscle, k. The bulbs
of the ciliae. I. Lubricating glands. w. Small hair on the skin of the lid. n.
The outer skin of the lids. o. Sweat-glands, p. Very fine hair. q. Conjunctiva tarsi.
(From Stellwag.)

(lacus lachrymalis) between them does not exist, as has been
generally taught in text-books.



OF THE HUMAN EYE. 147

The tarsal cartilages (tarsi) (d, Fig. 64) form the firm basis
for each lid. In structure they belong to the compactly
formed connective tissue, with a certain number of small
cartilage-cells bound up with it. They are semilunar in
shape, about O r// .3 to W" A thick, and are elastic. The upper
and larger is nearly one-half inch in breadth at the middle.
They have their inner angle more obtuse than the outer. The
outer ends project a short distance beyond the canthus. Tfce
lower has the same length as the upper, but is much more
narrow, thinner, softer, and is of a more fibrous character.
The anterior surface of the tarsal cartilages is covered by the
musculus orUcularis patyebrarum, with which it is connected
by a very yielding connective tissue, whilst its posterior sur-
face is firmly attached to the conjunctiva. Toward the orbital
border the cartilages become thinner, and terminate in a fascia-
like membrane (e, Fig. 64), which is connected with the orbital
border. This fascia tarso-orbitalis is in connection with the
tendon of the levator muscle of the lid, which expands into a
broad membrane, and is lost in this fascia. The tarsal carti-
lages are connected with the margo orbitalis by a cellulo-fibrous
connective tissue mass, which proceeds from its periphery, and
in some parts it is like fascia in structure, whilst in other parts
it consists simply of loose cellular tissue membrane. Four of
these fibrous bands have generally been described, two of
which unite the outer and inner ends of the cartilages, named
the ligamentum canthi internum and externum, and two of which
proceed from the border of the cartilages (e, Fig. 64) to the
margin of the orbit, in the form of flat, broad fascia-like mem-
branes, the ligamentum tarsilatum superius et inferius. Pilz
thinks that the ligamentum canthi internum can alone be con-
sidered a true ligament. The others are more like cellular
tissue, and have no well-defined borders.

The inner palpebral band or ligament (w, Fig. 65) is 2J'" to
3"' long, and about 2"' wide, and originates from the perios-
teum of the frontal process of the superior maxillary bone, runs
horizontally outward and is lost (7, Fig. 65) in the inner obtuse



148 THE ANATOMY AND HISTOLOGY

ends of the tarsal cartilages of the upper and lower lids. It
passes over the lachrymal sac, and at the commissure of the
lids it divides (?, Fig. 65), part accompanying the fibres of the

Fm. 65.




(From Pilz.)

orbicular muscle, which proceed from the lachrymal bone to
the lachrymal canals, the anterior and outer walls of which it
covers ; another process passes back to the eyeball, which is
continuous with the tunica vaginalis bulbi by a process. It is
this process that is adherent to the conjunctiva, and which is
an important fact to be noted in connection with the opera-
tion for squinting, as pointed out by Liebreich. It supports
the semilunar fold (plica semilunaris) and the caruncula lachry-
malis resting on it. Its upper and lower surfaces afford origin
for the portio anterior of ihQ'musculus orbicularis ; the anterior
border is immediately beneath the skin, and the posterior
border covers the inner half of the lachrymal sac, with
which it is firmly united, and serves to strengthen it.

The lig amentum canthi externum (s, Fig. 65) is not really a
ligament, but consists of a firm fibrous texture, and unites the
acute angles of the outer ends of the tarsal cartilages, and
with the firmly adherent skin, forms the outer eye-angle, and
is blended with the periosteum of the orbital border, and with
the process of Tenon's membrane. The cellular tissue mem-
brane that fills up the space above the ligamenta canthi, between
the tarsal cartilages and the border of the orbit, has been de-
scribed by authors as the ligamenta lata. This cellular tissue



OF THE HUMAN EYE.

in certain points is condensed into a firm structure, which
appears tendinous, and throughout its whole extent is loosely
connected with the orhicularis muscle, which rests on it, and
partly insheathes its fasciculi ; portions of it are attached to the
cellular tissue immediately in contact with the skin of the lids.

For a more special description of the cellular tissue mem-
brane of the lids, a division of the parts above and the parts
below the ligamenta canthi becomes necessary. In the cellu-
lar membrane of the upper division but three points are found
where a true fibrous structure is manifest : at the point of
insertion of the musculus levator palpebrce superioris (/, Fig. 65},
outward where it covers the lachrymal gland (A, Fig. 65), and
to which it sends processes (p), and over the trochlea (</), from
which a suspensory band is given off to the bulbus. In all
other portions of this part of the membrane it consists of cel-
lular tissue.

In the lower division of this cellular membrane, only one
point is characterized by the fibrous structure, which is a band,
and extends from the middle of the lower surface of the liga-
mentwn canthi internum, passing obliquely outward and down-
ward (m, Fig. 65), to a portion of the rim of the orbit between
the lachrymal sac and the origin of the musculus obliquus
inferior, and covers the outer surface of this muscle (o). In all
other parts this membrane is composed of cellular tissue.
Nearer the tarsal cartilage it disappears in the stroma of the
conjunctiva at the lower cul-de-sac (d, Fig. 65), and the band
of Tenon's membrane given off in that direction.

The Meibomian glands are imbedded in the tarsal cartilages,
nearer to the posterior than the anterior surface. On everting
the lids .they can be seen as parallel strings of pearls running
in a vertical direction. In structure and in the character of
their secretions they are like the sebaceous glands (/, Fig. 64).
They are in number about 30 in the upper cartilage and 20 to
25 in the lower. They do not extend throughout the whole
breadth of the cartilages, not reaching their attached border,
and are surrounded on all sides by the cartilaginous substance.



150 THE ANATOMY AND HISTOLOGY

In the main they are regularly vertical in their direction,
but sometimes their posterior ends are united, or they bend
over laterally and form a curve. Toward the palpebral border
the glands become larger. In structure they present numerous,
somewhat round, angular cryptce aggregates, with a diameter of
3 V' to \' n ', which surround in a horizontal direction a canal
of T y" to 4-'", and in certain cases J"' in diameter. The secre-
tion of the Meibomian glands is like that of the sebaceous
glands, and it is said (Kolliker) that the only difference is that
the fat does not collect into large drops, but remains in separate
particles. At the border of the lids it excretes the eye-butter,
the lema palpebralis, which is a whitish, rather thickish, fatty
substance, intended to prevent the adhesion of the lids.

The tarsal cartilages do not reach to the free border of the
lids within \ fff to J'", being covered by ordinary epidermis
and mucous membrane (Fig. 64). The ducts open on the
free borders of the lids (c, Fig. 64), the mouths of which are
0'".04 to 0'".05 in diameter. The tubes consist of basement
membrane, covered by a layer of scaly epithelium. The outer
skin of the lids is delicate and thin, easily raised into folds.
It has a thickness of about \"' to \' n '. Its tela cellulosa sub-
cutanei is poor in fat, and its inner surface is connected by a
loose cellular tissue to the orbicularis muscle and the palpebral
bands above described.

The outer layer of the subcutaneous cellular tissue is con-
nected with the corium by a large number of cords of connec-
tive tissue, and is not sharply divided from it. This subcuta-
neous cellular tissue varies in thickness according to age, sex,
and individuality, depending chiefly on the amount of fatty
tissue in it. According to Krause, the thickness of the sub-
cutaneous cellular tissue, void of fat, is \ nf . The corium, which
is an inelastic skin, mostly made up of connective tissue, con-
sists, in most parts, of two layers, especially where it rests on
adipose tissue the pars reticularis and trabecularis. In the
eyelids there is only one layer, the structure of which has the
pars papillaris with very short papillae, which in fact are some-



OF THE HUMAN EYE. 151

times entirely wanting. The corium is \" r to \ f " only in thick-
ness.

The skin of the eyelids contains sweat-glands (Fig. 64), which
extend to the very border, and measure about -^"' to T V",
and are not located, as is common, in the pars reticularis, but
are in the subcutaneous cellular structure, or in the border
thereof. The ducts of the glands have delicate walls, and are
without muscles. The skin also possesses many small hairs
(Fig. 64), which differ from the cilise in not having sebaceous
glands at their sides (Kolliker).

Toward the orbital border the skin becomes thicker, and
toward the lower border of the orbit it is richly supplied with
adipose tissue.

The orbicularis palpebrarum muscle (musculus orbicularis) is a
sphincter muscle, which is expanded beneath the integument
of the lids, and around the circumference of the orbit, extend-
ing some distance beyond the border of the latter (see Figs., 66
and 67). We are indebted to Professor Arlt, of Vienna, for
a clear description of this muscle, and what follows is mostly


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Online LibraryAbraham MetzThe anatomy and histology of the human eye → online text (page 11 of 14)