. Animal physiology. Physiology, Comparative; Physiology, Comparative. STRUCTURE OF THE EYE OP MAN. 401 532. Now the Eye, in its most perfect form—such as it possesses in Man and the higher animals—is an optical instru- ment of wonderful completeness, designed to form an exact picture of surrounding objects, upon the expanded surface of the optic nerve, by which the impression is conveyed to the brain. As it is in the most perfect form of this instrument, that we are best able to judge of the uses of its different parts, it will be preferable to consider this in the first instance, and then to
. Animal physiology. Physiology, Comparative; Physiology, Comparative. STRUCTURE OF THE EYE OP MAN. 401 532. Now the Eye, in its most perfect form—such as it possesses in Man and the higher animals—is an optical instru- ment of wonderful completeness, designed to form an exact picture of surrounding objects, upon the expanded surface of the optic nerve, by which the impression is conveyed to the brain. As it is in the most perfect form of this instrument, that we are best able to judge of the uses of its different parts, it will be preferable to consider this in the first instance, and then to advert to the less complete forms, which we meet with in the lower animals. 533. The Eye of Man, and of all the Vertebrata, has a nearly globular form. The walls of the sphere are composed of three coats ; whilst in its interior are found three humours of a more or less fluid character. The outer coat, earned the sclerotic (s, Fig. 197), is tough and fibrous, and is destined to support and protect the delicate parts which it contains. It does not cover the whole globe, however; but gives place in the front of the eye, to a transparent lamina of cartilaginous structure (c), which is termed the cornea. The manner in which this cornea is set upon the sclerotic coat, serving ch s, cr b as the continuation of it, may be compared to that in which a watch-glass serves as the conti- nuation of the watch-case over the dial. The cornea is rather more convex than the rest of the sphere of the eye ; so that the globe makes a slight additional projection in that part. When the sclerotic coat is removed, FlG. ^.-interior of the eyb. We come Upon the second COat, c> cornea ; s, sclerotic ; s', portion of 1 • v • , j ii 7 -7/7\ tne sclerotic turned back to show the Which IS termed the Choroid (Ch); subjacent parts ; eh, choroid ; r, retina ; this is much more delicate in its »>.°Pticnerve; ca, anterior chamber; i, iris, p, pupil; cr, crystalline lens; pc, Structure, and Consis
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