(From cornu, as it resembles horn). A coat of the eye, which is also called sclerotica cera-ioides. It is the first proper coat of the eye, strong, thick, and tendinous; its anterior part is distinguished by the name of cornea transparens, or lucida, and the posterior part by that of cornea opaca. The transparent part is sometimes called cornea; and the posterior part cornea opaca, and sclerotica, or sclerotis: the former only is elastic. The opake part is made up of several laminae closely connected, whose fibres run in different directions, and form a dense, compact substance.
The cornea consists of an external and internal lamina, each of which is composed of thinner laminae. Its substance is in some degree elastic, to fit the eye to different magnitudes and distances; it is also perforated with many small holes, through which a fluid is supposed to be constantly discharged, but which soon evaporates.
The sclerotica and cornea are furnished with arteries, chiefly from a branch of the internal carotid. The nerves proceed principally from the ophthalmic branch of the fifth pair.
The cornea transmits the rays of light into the eye, and produces the first refraction of the rays necessary to vision. Its natural transparency is liable to be obscured by inflammation, by abscesses, and ulcers.
It seems more proper to consider this coat of the eye as the sclerotica, and the cornea only as its transparent part. See Sclerotica.