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central region, immediately around the anterior pole and the
marginal region, extending outward as far as the edge of the
lens. In the central region, the epithelium is a delicate pave-
ment, formed by a single layer of large polygonal cells, joined

FIG. 34.




Intra-capsular epithelium, central region. (From Hulke.}

edge to edge ; the cells are conspicuous for their sharp outlines,
and each contains a large circular nucleus, which, in turn, in-



-86



THE ANATOMY AND HISTOLOGY



closes two or three small dark dots or nucleoli. The imcleoli
are remarkable for their uniform size and regular circular out-
lines ; they occupy the centre of the cells, and each nucleus is
separated from the neighboring ones by a space about equal to
its own diameter.

In the marginal region the epithelial cells are much smaller
and more closely packed together. The nuclei are smaller,
have a less regular outline, and are separated by extremely
minute intervals ; indeed they are sometimes almost in contact,
and the Avails of their containing cells can hardly be made out.
The epithelium in this region is not arranged as a simple
pavement, but rather in the form of a bed, in which the cells
are crowded in superimposed layers ; the bed is not prolonged
beyond the edge of the lens, and the inner surface of the pos-
terior hemisphere, of the capsule is void of epithelial lining.

The transition from the large polygonal cells of the central
region to the small crowded ones of the margin is not abrupt ;
every possible gradation occurs between these extreme forms.

EIG. 35.




Intra-capsular epithelium of the marginal region, constituting the matrix of the lens.

(Fiom Hul/.e.)

This epithelial bed at the margin of the anterior half of the
capsule is the matrix of the lens ; in the young it contains free



OF THE HUMAN EYE.



87



nuclei ; and it is the growing part in which the lenticular fibres
are formed by the growth and metamorphosis of the cells.

Becker says that the smallest of these embryonic cells
are found in groups in the protoplasma, from two to six in a



FIG. 36.




Cells of the matrix undergoing transformation into lenticular fibres. (From Hulke.)

group, as seen in Fig. 37 at a, which are constantly being
crowded back.

FIG. 37.

'"^




Their nuclei become larger, more round, isolate themselves
more, and take such a position, that, finally, they are found
in rows behind each other, as seen at c, Fig. 37.

Up to this time there are no well-defined cell-walls, but
from this point they are recognized. These cells, arranged in

FIG. 38.




Vertical lens-fibres seen from the capsule. From a dove's eye. Magnified 230 times.

(From Becker.)

rows, begin to grow in length, and still' further separate them-
selves. After having reached a certain length they form neat



OS THE ANATOMY AND HISTOLOGY

convolutions, as they assume a more oblique direction back-
ward. These fibrercells, or lens-fibres, thus originated, are
crowded more and more inward to the lens, so that finally
their position is changed, and they enter into the concentric
laminse of the lens as lenticular fibres. (See Fig. 36.)

The embryonic cells, which, at first, are round, as they
increase in volume, being surrounded on all sides by growing
cells, necessarily assume a hexagonal form, as seen in Fig. 38.

At the point where they curve, the strongest pressure
naturally takes place in front, which, therefore, is more thin
here, whilst back, toward the capsule, they expand more.
The further inward, toward the centre of the lens, that the
fibres are situated, the more flattened they become, until
they are found as flattened hexagonal bands. Their ends,
anteriorly as well as posteriorly, overlap each other in the
form of shingles on a roof, as seen in Fig. 39.

FIG. 39.



Ends of lenticular fibres abutting on the lens-capsule. Side view. From the lens of
a calf. Magnified 230 times. (From Bec/.er.)

In the neighborhood of the equator of the lens the ends of
the fibres are broader than the fibres themselves, as seen in

FIG. 41.



FIG. 40.



Showing serrated edges of the
fibres of the lens. (Becker.)




Serrated lenticular fibres
from the lens of a cod.



Fig. 39. Further back the fibres become more thin and nar-
row, and on the edges are usually serrated, as seen in Fig. 40.



OF THE HUMAN EYE.



89



In the fish and amphibia the fibres are much more ser-
rated, as seen in Fig. 41.

As soon as the lenticular fibres have reached the star, their
natural boundary, that prevents further growth, a change
takes place in their form. Instead of continuing their course,
the ends turn nearly perpendicularly away from their former
course, as seen in Fig. 42, Fig. 43, and Fig. 44.



FIG. 43.



FIG 42.




Termination of lens-fibres
against a star ray. (Becker.)




FIG. 44.



Termination of lens-fi-
bres against the central
canal. (Becker.)



A single fibre terminat-
ing against the ray of a
star. (Becker.)



In Fig. 44 there is a single fibre showing the manner in
which the ends curve. The walls of the star are pressed
closely together ; still the hexagonal form of the ends remain
visible.

The youngest fibres have but a very delicate enveloping
membrane, which is easily ruptured, and allows its albumi-
noid contents to escape. Later, the contents of the fibres
become more solid, so that it will escape only from its ends.

In the older text-books there is given a description of the
liquor Morgagni, a thin albuminoid substance between the
lens and the capsule. More recently it has been discovered
that this liquid is collected by some post-mortem change,
supposed to be a solution of the epithelial cells.

Becker says that the epithelial cells are not readily dis-
solved, and he believes the liquon Morgagni to be composed
of the escaped contents from the ends of the lenticular fibres,
along with the substance contained in the stars.



90 THE ANATOMY AND HISTOLOGY

At birth the multiplication of new fibres is quite active,
but diminishes as age advances ; the zone of embryonic cells
becomes more narrow, yet the new formation of lenticular
fibres progresses, though slowly, the deep-seated fibres near
the centre of the lens atrophy, the lens becomes more solid,
less elastic, and more flattened ; all of which, obviously,
has its influence on the accommodative act, with such reg-
ularity that it may be denominated a fixed physiological
law, as Donders has taught that emmetropic eyes have a
certain accommodative power at a certain age. The matrix
being situated at the equator (a constant deposition of new
fibres taking place there) accounts for the flattening of the
lens in old age. The lens itself is composed of the lenticular
fibres and the interstellar and the interfibrous substance
(Becker). The lenticular fibres are flat, six-sided elements,
which, according to Kolliker, have a breadth of 0'".0025 to
0'".005, and a thickness of 0'".0009 to 0'".0014, and are per-
fectly clear, pliable, and soft.

Their breadth and thickness is modified by age, and by the
position of the fibres, whether located near the nucleus or near
the surface. Near the nucleus the fibres are mere flattened
bands in adult persons. (See Fig. 45.)

FIG. 45.




Lnyer of lenticular fibres cut vertically so as to show their hexagonal form.

They are delicate walled tubes, containing a clear, viscid,
albuminoid matter, and they become darker and more dis-
tinct in all substances that coagulate albumen ; and therefore
chromic acid, nitric acid, alcohol, and sulphuric acid, are used
to harden the lenticular master to facilitate its investigation.

For a long time, the lens has been divided by anatomists
into a cortical portion, and the nucleus. According to recent



OF THE HUMAN EYE. 91

liistological investigations it is not strictly correct. It is true
that in a certain sense we have a nucleus, and a cortical por-
tion ; but there is nothing like a distinct separation between
the two, but a gradual change from the soft tubular condition
of the surface, to the more solid, fibrous structure of its central
part.

The lens has also been described as lamellated, consisting of
layers like an onion. This is true only to this extent ; the
lenticular fibres separate more readily on their external or in-
ternal surfaces than on their sides, where the surface is ser-
rated. So there is nothing like regular layers, but any number
of fibres may be peeled off, according to .the character of the
force applied. In short the lenticular fibres constitute the fun-
damental elements of this organ, being composed of the super-
induced fibres, from the very centre to the periphery.

The stellate figures have quite different forms at different pe-
riods of life. We find them in their most simple form in the
foetus, and in new-born children, with a star of three rays,
which regularly meet, on the anterior surface of the lens, in an
angle of 120, with two rays pointing obliquely downward,
and one vertically upwards. On the posterior surface of the
lens this figure is inverted, the two rays being directed ob-
liquely upward, and the vertical ray, downward, in the form
of the letter Y.

FIG. 46.




In Fig. 46, taken from Pilz, the dark lines represent the an-
terior surface, and the dotted lines the posterior surface.

The posterior star, compared with the anterior, appears as if
turned round through an angle of 60. The direction of the



92 THE ANATOMY AND HISTOLOGY

lenticular fibres in the individual laminae is as follows : No in-
dividual fibre traverses the entire semi-circumference of the
lamella, as a fibre starting from the axis of the lens, either on
its anterior or posterior surface, will not reach the lens-axis of
the opposite surface, but immediately after curving round the
equator, will attach itself to the end of the ray close to the
equator. Or, reversing it, say a fibre starts from the very end
of a star-ray, it will curve round the equator and terminate at
the lens-axis of the opposite surface.

FIG. 47. FIG. 48.





Fig. 47 represents the anterior surface of the lens of a child, and Fig. 48 the posterior
surface. (From Nutinely.)

On looking again at Fig. 46, it will be observed that the
longest dark lines representing the fibres on the anterior sur-
face, are the shortest on the posterior surface, represented by
the dotted lines, and vice versa. This is the mode of extension
of all the lens-tubes, none of them going quite round, and all
those which lie in one layer being of equal length. In the
adult the nucleus of the lens presents exactly the same condi-
tion, but on the other hand, in the superficial lamellse, and on the
surface itself, a more compound star is found, having from nine
to sixteen rays, of various lengths, and rarely quite regular ;
still, however, certain main rays may even here be distinguished
from the others. (See Fig. 49.) The course of the fibres neces-
sarily becomes more complicated by this means ; and the more
so, as on such stars the fibres attached to the side of the rays



OF THE HUMAN EYE.



93*



converge in an arcuate manner, giving rise to a penniform or
whorled appearance (vortices lentis). But nevertheless, the es-
sential points of the course of the fibres just described remain
completely the same, seeing that in these more complex stars
the rays of the anterior and posterior aspects do not corre-
spond, and that no fibre goes from one pole to the other.

FIG. 49.




Lens of the adult, after Arnold, to show the stars. 1. Anterior surface ; 2. Posterior

surface.

As the stars pass through all the laminae, there exist three
or more perpendicular non-fibrillated planes, called central
planes by Bowman (Kolliker). The manner in which the
fibres terminate at the stellate figures, has been alluded to
above.

Fig. 50, from Becker, shows their mode of termination.

FIG. 50.




Terminations of lenticular fibres, the large ends terminating in the stars. (BecJ.er.)

In the stars, says Kolliker, the substance of the lens is not
formed of tubes, as elsewhere, but consists of a material, which
is, in part, finely granular, in part homogeneous.

Becker, who seems, most patiently, to have looked into this



94



THE ANATOMY AND HISTOLOGY



matter, says, that in the fresh state, the substance in the stars
is thick, altogether homogeneous, as clear as water, and of the
same index of refraction as the fibrous part. It becomes finely
granulated by coagulation, by boiling, also, in the mineral
acids, and in alcohol, and in alkalies is re-dissolved, and has the
general properties of protein substances.

This substance is not confined to the stars, but is wedged in
between the fibres of the lens. Becker asserts that this homo-
geneous substance fills a series of channels that communicate
in the equatorial region of the lens.

Fig. 51 shows the interfibrous channels in the lens of the calf.

FIG. 51.




Radiary splitting of a lamella of the lens, embracing nearly the half of it. It shows
the interfibrous channels, which are seen to cross each other. Magnified 65 diameters.
(From Becker.)

The homogeneous substance filling the interfibrous channels
is coagulated, and is represented by the dark lines.



Corpus Vitreum.

The histological structure of the vitreous body is but imper-
fectly understood, and it has for a long period been the object



OF THE HUMAN EYE. 95

of animated discussions among microscopists. Its structure
seems to be a peculiar one in the economy, and in the attempt
to place it among the various tissues it resembles, authors have
most widely differed.

The descriptions of Hanover and of Finkbeiner seem to be
sustained better, by more recent histologists, than those of any
other authors. Their views are not adopted, however, by some
high authorities. Further investigation must be awaited,
before anything like a positive histological description can be
given of this body.

The vitreous body fills up the space between the lens and
the retina, and through the zonula Zinnii is connected with
the lens. It lies loosely on the retina, except at the optic
nerve entrance, where its connection is more intimate, and
with the corona dliaris and the lens it is quite firmly connected.

The enveloping membrane (membrana hyaloidea) is an ex-
tremely delicate membrane, scarcely perceptible under the
microscope, and measures 0' 7/ .002. This is true, only of that
portion back of the ora serrata ; in front of this point, it be-
comes more firm, and is known as the pars dliaris hyaloidece
sen zonula Zinnii, and named by Retzius, ligamentum suspen-
sorium lentis, and proceeds to the border of the lens, to become
blended with its capsule, in the manner hereafter to be de-
scribed.

In structure, the vitreous body is a clear glass-like (vitrina
ocularis} substance, described by Virchow as a homogeneous,
muciferous substance, and by Kolliker as belonging to the
primitive forms of gelatinous connective tissue, bearing a con-
siderable resemblance to the enamel organ of the embryonic
dental sac. This substance is enveloped in a system of mem-
branes, which proceed from the surface of the hyaloid mem-
brane, and toward the centre, in the form of radii, dividing
the vitreous humor into sections like an orange.

Hanover made this discovery, on eyes immersed in chromic
acid, and later, Finkbeiner corroborated this, by investigations
made on eyes immersed in a solution of bichloride of mercury.



96 THE ANATOMY AND HISTOLOGY

All the sections converge toward the optic axis, which is the
space occupied in the embryo by the arteria centralis in the
canalis hyaloidea.

This canalis hyaloideus sen Cloquetii has its beginning in the
region of the papilla nervi optici, and is named the area Morte-
giana, and is the common axis of all the sections. The sections
do not quite reach the axis of the eye, but a cylindrical space
is left centrally, without membranous structure, and which is
considerably larger in the child than in the adult.

The walls of the sections gradually become more delicate,
until they can no longer be discerned. Hanover counted 180
radii in the human eye, and he believes that to be the sum of
the sections composing the vitreous body.

Finkbeiner claims that the section walls are the same in
structure as the membrana hyaloidea, having on each side a
layer of pavement-cells.

This division into sections, as taught by Hanover, and later,
by Finkbeiner, is sustained by Pilz, Bowman, Heiberg, and
others.

Pilz says this cannot be an error, such as Briicke was led
into, when he thought the vitreous body laminated, resulting,
Pilz thinks, from the effect of the solution of the acetate of
lead, which he used as a hardening remedy. The hyaloid
membrane must be divided into the portion that envelops the
vitreous body, and that portion extending from the beginning
of the ora serrata to the capsule of the lens.

Whilst this membrane, in the back part of the eye, envelops
the corpus vitreum as a single membrane, it divides itself, in
the region of the ora serrata retince, into two plates, of which
the posterior one forms the anterior wall of the vitreous body,
its anterior surface forming a dish-shaped concavity (fossa
hyaloidea) for the reception of the posterior surface of the lens ;
whilst its posterior surface forms the basis for the sectional
divisions above described.

The anterior division proceeds forward, toward the lens,
its outer surface being covered by the ciliary processes, and



OF THE HUMAN EYE. 97

before it reaches the equator of the lens, it again divides into
two laminae, an anterior and a posterior, the former being
corrugated and proceeding to the anterior lens-capsule, with
which it becomes blended ; the latter going to the posterior
capsule, uniting with it in the same manner. The anterior
corrugated, plaited lamina, on which rest the processus ciliares,
is the zonula Zinnii. The triangular space around the lens
equator, formed by the last-named division, is Petit' s canal, or,
the canalis godrome (Fig. 1, C P). In this division, it will be
observed that between the anterior surface of the posterior
lamina, forming the fossa hyaloidea, and the posterior surface
of the posterior lamina of the second division, going to the
posterior lens-capsule, another longer, but more narrow canal
is formed, the canalis Hanoveri (Fig. 1, C H). According to
Finkbeiner, the hyaloid membrane is composed of a fibrous
texture, covered with an epithelial layer.

The former is composed of an innumerable mass of delicate
elementary connective tissue fibres tied together, which have
a fine striation, and finally, in their course, end in true con-
nective tissue. These fibres are too fine for measurement,
and in acetic acid they swell, and finally disappear, leaving
finer, darker and shorter threads, which are supposed to be
nuclei.

At the ora serrata, where the membrana hyaloidea is inti-
mately connected with the retina, these fibres become more
visible, unite, and form a texture, very similar to connective
tissue. Further forward, beneath the processus ciliares, they
unite more intimately, and anastomose, until broad bundles
are formed, which from hence proceed to the lens-capsule in
two forms, which there expand as bands and fibres, to unite
with the capsule ; or beneath the ciliary process, they divide
dichotomously, and are united to the lens-capsule by fine fibres,
which can be traced from the ciliary processes.

Beneath the processus ciliares, Finkbeiner discovered a trans-
verse striation of these fibres, which Retzius had already dis-
covered. Toward the borders of the ciliary processes it begins

7



98 THE ANATOMY AND HIST-OLOGY

to fade, and in the thinnest part of the zonula Zinnii it cannot
be discerned. Finkbeiner could not demonstrate that they
are muscular fibres. Pappenheim, Ammon, Henby, Sappey,
Bendz, Frey, Kolliker and Weber agree that these fibres re-
semble connective tissue, or elastic fibres. Heiberg, who has
recently gone over this ground, concludes that the zonula does
not suddenly divide at the ora serrata, but that even back of
that point, fine fibres originate, which, by lateral anastomoses,
proceed forward, to form beneath the ciliary processes more
firm bundles, which finally unite in a continuous membrane,
which follows all the elevations and depressions of the processus
ciliares, and at the same time connecting with the parts beneath,
so that the pars ciliares retinae and the choroidal epithelium all
fall together when the zonula is forcibly detached. Just be-
fore reaching the ciliary processes, this membrane divides,
one plate going to the anterior capsule of the lens, and the
other to the posterior capsule, thus forming between them, the
canalis Petiti.

This would still leave the true hyaloid membrane, which
proceeds forward, and forms the anterior wall of the vitreous
body and the hyaloid fossa. Between the posterior lamina of
the ligameiitum suspensorium lentis and the hyaloid membrane,
the canalis Hanoveri, described above, is formed.

When the parts are removed, so that the connection be-
tween the zone of Zinnius and the lens can be seen, it will be
perceived that it surrounds the lens like a belt. The fibres at
the lens-capsule expand, and in a zigzag form are connected
with it. Each bundle of fibres with its pointed surface is con-
nected with a ciliary process. The zone has, as a connective
material, a thin, structureless, vitreous membrane, much cor-
rugated, with two kinds of fibres, those with longitudinal
striae, and the more numerous, with transverse striae. (See
Fig. 52.) The fimbriated end is attached to the capsule.

The fibres seem mostly to originate from the membrana
hyaloidae, but a portion of them seem connected with the
cells of the pars ciliares retinae, which Kolliker asserts to



OF THE HUMAN EYE.



99



be connective tissue, and which is a continuation of the radiary
or connective tissue fibres of the retina. Heiberg has not seen



FIG. 52.




Fibres from the zonula of man ; a, prepared in Mutter's solution ; b, prepared in
solution of nitrate of silver ; c, a piece of the capsule. Magnified 300 diameters. (From
Heiberg.)

these cylindrical cells in man, in the process of transformation
into the zonular fibres, but believes he has discovered them in
the sea-dog. In separating these cells, their inner ends are
often seen with anastomosing points, as in Fig. 53, and some-
times they terminate in a thread-like process ; as in Fig. 54.

FIG. 53.




Cells from theirs ciliares retince, the points, a, anastomosing. Human Eye, magnified
350 diameters. (From Heiberg.)

Heiberg could not positively determine in man, that the
fibres of the zonula Zinnii are muscular, his only test being
the microscope. In the horse, he is satisfied that he discovered



100 THE ANATOMY AND HISTOLOGY

muscular fibres in the zone ; and analogy, as well as the results
of his microscopic investigations, cause him to believe that



FIG. 54.




Showing a thread-like process, b. (Heiberg.)

there are muscular fibres also in the zonula of man. It has
contractile tissue. It is one of the important parts concerned
in the accommodative process. The contraction of the zonular
fibres in connection with the radiary fibres of the ciliary mus-
cle, extends, or enlarges the equatorial diameter of the lens,
and diminishes the antero-posterior diameter, and fixes the
eye for remote vision. These two sets of fibres are the active
agency in the so-called negative accommodation. They are
doubtless antagonistic to the circular fibres of the ciliary
muscle.

When the circular fibres of the ciliary muscle contract, they
overcome the tension of the zonular fibres, and the lens, by
its inherent elasticity, has its antero-posterior diameter en-
larged, and the eye is fixed for near vision.

The circular fibres of the ciliary muscle, then, are the active
agency concerned in vision for near objects, or in positive ac-
commodation ; the fibres of the zone of Zinnius in connection
with the longitudinal fibres of the ciliary muscle, are the active
agency in accommodation for remote objects, or for negative
accommodation. This agrees with the observations made by
Otto Becker of Vienna, that during the accommodative act,
the ciliary processes retract, and during life, at no time, do
they proceed as far forward as the lens equator, and that by



OF THE HUMAN EYE. 101

their contraction they cannot cause pressure on the equatorial
surface of the lens, and thus cause the sides to bulge out, in-
creasing the antero-posterior diameter of the lens, and fixing


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