. Outlines of zoology. Zoology. S£JVS£ ORGANS. 449 snakes and lizards, and its nerves are abortive in the mole. The adult eye is more or less globular, and its walls con- sist of several distinct layers. The innermost layer bound- ing the posterior part of the globe is the sensitive retina, innervated by fine branches from the optic nerve. It may be compared to the nervous matter of the brain, from which, indeed, it arises. Outside of the retina is a pigmented epithelium, and outside of this a vascular membrane; together these are often called the cho- roid. The vascular part may be com- pared
. Outlines of zoology. Zoology. S£JVS£ ORGANS. 449 snakes and lizards, and its nerves are abortive in the mole. The adult eye is more or less globular, and its walls con- sist of several distinct layers. The innermost layer bound- ing the posterior part of the globe is the sensitive retina, innervated by fine branches from the optic nerve. It may be compared to the nervous matter of the brain, from which, indeed, it arises. Outside of the retina is a pigmented epithelium, and outside of this a vascular membrane; together these are often called the cho- roid. The vascular part may be com- pared to the pia mater covering the brain, and like it is derived from meso- blast. Outside of the choroidis aprotective layer or sclerotic, comparable to, and continuous with, the dura mater covering the brain, and also mesoblastic in origin. Occupying the front of the globe is the crystalline lens, a clear ball derived directlyfrom the skin. Fig. 191.—Diagram of the eye. C, Cornea; , aqueous humour; , ciliary body; L, lens; /., Iris; Sc, sclerotic; Ch., choroid; retina; z/.A., vitreous humour; , yellow spot; «., optic nerve. It is fringed in front by a pigmented and muscular ring—the iris, which is for the most part a continuation of the choroid. The space enclosed by the iris in front of the lens is called the pupil. Protecting and closing the front of the eye is the firm cornea continuous with the sclerotic, and covered externally by the conjunctiva —a delicate epithelium continuous with the epidermis. Between the cornea and the iris is a lymph space containing aqueous humour, while the inner chamber behind the lens contains a clear jelly—the vitreous humour. The lens is moored by " ciliary processes " of the choroid, and its shape 29. 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 orig
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Keywords: ., bookauthorth, bookcentury1800, bookdecade1890, booksubjectzoology
