THE SPECIAL SENSES. 



131 



the pupil. The eye-ball, or globe, rests upon a soft cushion 

 of fat. This gives it an easy support and allows it to move 

 about with the utmost freedom. 



7. The Coats of the Eye. The eye has three coats. 

 The back part of the outer covering, the " white of the eye," 

 is called the sclerotic coat. It is a dense, firm membrane, 

 and preserves the shape of the eye. In front, the outer coat 



FIG. 39. The Eye: a, crystalline lens; b, the retina; c, the cornea; 

 d, the sclerotic; e, the choroid; g, capsule of lens; h, vitreous humor; 

 i, iris ; k, pupil ; o, optic nerve. 



is thin and transparent, and is called the cornea. It is the 

 window through which light is admitted. 



The second coat, the choroid, lines the outer coat at the 

 back. It is a layer of black substance intended to absorb 

 the surplus light in order that objects may be clearly seen. 

 The third is the retina, a delicate membrane in which are 

 distributed the branches of the optic nerve. It is the inner- 

 most coat and lies on the choroid. 



