. Elements of comparative zoology. Zoology. 304 SYSTEMATIC ZOOLOGY. sclerotic coat, which is usually white (the white of the eye is part of it), and which may be cartilaginous or may even have bone deposited in it, as in many reptiles and birds. In front this layer becomes perfectly transparent, and is there known as the cornea. Inside of the sclerotic is found a densely black layer (choroid), and still within this the transparent retina, the outer portion of which is. FIG. 113.—Diagram of vertebrate eye. c, choroid i| -^iris; I, lens; n, optic nerve; r, retina; s, sclerotic. imbedded in the c
. Elements of comparative zoology. Zoology. 304 SYSTEMATIC ZOOLOGY. sclerotic coat, which is usually white (the white of the eye is part of it), and which may be cartilaginous or may even have bone deposited in it, as in many reptiles and birds. In front this layer becomes perfectly transparent, and is there known as the cornea. Inside of the sclerotic is found a densely black layer (choroid), and still within this the transparent retina, the outer portion of which is. FIG. 113.—Diagram of vertebrate eye. c, choroid i| -^iris; I, lens; n, optic nerve; r, retina; s, sclerotic. imbedded in the choroid. In front the choroid is con- tinued into the iris, a circular muscle with an aperture, the pupil, in its centre. This iris, which is colored, regu- lates by its enlargement and contraction the amount of light which is admitted to the visual parts of the eye. Back of the iris, and held in position by a circular muscle and ligament, is the transparent lens. In front of this lens is a watery fluid (aqueous humor), while behind it and between it and the retina is the somewhat denser vitreous humor. The optic nerve enters the eye from behind, passing. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Kingsley, J. S. (John Sterling), 1854-1929. New York, H. Holt and Company
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