894. The COATS are three in number: 1st. The Scle-rot´ic and Corn´e-a. 2d. The Cho´roid, Iris, and Cil´ia-ry processes. 3d. The Ret´i-na.
895 The HUMORS are also three in number: 1st. The A´que-ous, or watery. 2d. The Crys´tal-line, (lens.) 3d. The Vit´re-ous, or glassy.
Fig. 137.
Fig. 137. The second pair of nerves. 1, 1, Globe of the eye: the one on the left is perfect, but that on the right has the sclerotic and choroid coats removed, to show the retina. 2, The crossing of the optic nerve. 5, The pons varolii. 6, The medulla oblongata. 7, 8, 9, 10, 11, 12, 13, The origin of several pairs of cranial nerves.
896. The SCLEROTIC COAT is a dense, fibrous membrane and invests about four fifths of the globe of the eye. It gives form to this organ, and serves for the attachment of the muscles that move the eye in various directions. This coat, from the brilliancy of its whiteness, is known by the name of “the 396 white of the eye.” Anteriorly, the sclerotic coat presents a bevelled edge, which receives the cornea in the same way that a watch-glass is received by the groove in its case.
894. Name the coats of the eye. 895. Name the humors of the eye. Explain fig. 137. 896. Describe the sclerotic coat.
897. The CORNEA is the transparent projecting layer, that forms the anterior fifth of the globe of the eye. In form, it is circular, convexo-concave, and resembles a watch-glass. It is received by its edge, which is sharp and thin, within the bevelled border of the sclerotic, to which it is firmly attached. The cornea is composed of several different layers; its blood-vessels are so small that they exclude the red particles altogether, and admit nothing but serum.