170 ANTHROPOLOGY. 
of the sclerotic, being the segment of a smaller sphere engrafted on the 
larger one formed by that membrane. It is perfectly smooth and trans- 
parent, circular in form, although the transverse diameter is slightly larger 
than the vertical. In man it is a concavo-convex lens of slight refracting 
power, owing to the fact of its greater thickness in the centre than at the 
edges. The margins of the sclerotic are bevelled off obliquely, the outer 
lamina extending further than the inner; between the edges there is a 
shallow groove, into which the cornea is fitted like a crystal in a watch. | 
The cornea consists of several layers, some of these exceedingly delicate. 
Exteriorly there is a fine epithelial lamina, constituted by the prolongation 
of the conjunctiva. This becomes opake after death, causing the peculiar 
film over the eye. Next comes the cornea proper, consisting of transparent, 
soft, flexible lamine, connected together by delicate areolar tissue. Pos- 
terior to the proper laminated cornea is a thin, strong, elastic, cartilaginous 
lamina, the membrane of Demours ; it is perfectly transparent, and is placed 
between the cornea and the membrane of the aqueous humor. It extends 
beyond the proper cornea, and fits in by a well defined margin between the 
sclerotic and the ciliary ligament. The fourth layer of the cornea is the 
membrane or capsule of the aqueous humor, a tissue of exquisite delicacy. 
The choroid coat is the second tunic of the eyeball, and is so named from 
an imaginary resemblance to the chorion of the gravid uterus. It is a soft 
membrane of a dark brown color, extending from the optic nerves as far 
forwards as the ciliary ligament, which is internal to the line of junction 
between the cornea and sclerotic, and external to the iris. This ligament 
and the iris may be considered as appendages to it. It is pierced posteriorly 
by an annular foramen for the passage of the optic nerve; anteriorly it 
presents a large opening for the iris. The choroid is extremely vascular 
and organized, and serves not only as a connecting medium between 
different parts of the organ, but also for conducting vessels and nerves to 
the interior, especially to the iris; it also secretes the dark pigment of the 
eye. This is deposited throughout its substance, more thickly, however, 
internally ; the sclerotic is stained by it, but not the retina. This peculiar 
secretion is intended to darken the interior of the eye, as is done in the 
interior of optical instruments, to absorb the rays of light and to prevent 
their being reflected back again to the retina. 
3. Tae Cruiary Ligament is a soft, spongy, fibro-cellular, annular band, 
of a greyish white color, not stained by pigment. It is continuous with the 
anterior margin of the choroid, internal to the line of junction between the 
cornea and sclerotic. The iris is inserted into its external border, and 
from its anterior aspect are continued the ciliary processes or folds of the 
choroid membrane. It thus serves as a common central medium to con- 
nect the various tissues of the eye. 
4, CintAry Processes, or corpus ciliare, are delicate folds or plaits of 
the choroid membrane, extending from within the ciliary ligament to the 
back part of the iris, and thence along the fore part of the vitreous humor 
to near the circumference of the crystalline lens; the entire series resem- 
bles the disk of a composite flower. 
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