l70 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 refractinor 

 power, owing to the fact of its greater thickness in the centre than at the 

 edges. The margins of the sclerotic are bevelled oft' obliquely, the outer 

 lamina extending further than the inner ; between the edges there is a shal- 

 low groove, into which the cornea is fitted like a crystal in a watch. The 

 cornea consists of several layers, some of these exceedingly delicate. Ex- 

 teriorly 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 laminae, connected together by delicate areolar tissue. Posterior to 

 the proper laminated cornea is a thin, strong, elastic, cartilaginous lamina, 

 the viemhrane 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 liumor, 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 difter- 

 ent 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, inter- 

 nally ; 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. The Ciliary 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 connect the 

 various tissues of the eye. 



4. Ciliary 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 resembles the 

 disk of a composite flower. 



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