ANATOMY OF THE HORSE'S EYE. 



[When reading note the location of the parts of the eye as illustrated 



in Fig. 1.] 



Tlie eyeball or globe is a spherical shell whose interior 

 is filled with liquid or semi-liquid parts, called the humors 

 or refractiug media of the eye. 



The wall or shell of the eye is formed by three distinct 

 coats — the external, the middle and the internal. 



The outer or external coat is divided into two distinct 

 parts — the sclerotica and the cornea. 



The sclerotic is a very tough, white membrane, forming 

 about four-fifths of the outer coat of the eye. The muscles 

 that move the eyeball are attached to the back part and the 

 outer surface of the sclerotica. Its internal surface is loosely 

 • united to the middle or choroid coat of the eye by small 

 blood vessels, nerves and loose fibrous tissue. In front, the 

 sclerotica shows an elliptical opening with its greatest diam- 

 eter from side to side and shortest diameter from above to 

 below; the edge or border of this opening is bevelled on the 

 inner side, and the cornea fits in it as the watch crystal fits 

 in the watch case. 



The sclerotic is well supplied with blood vessels and nerves, 

 and a little below the middle of the back part, the optic nerve 

 passes through it and the choroid to form the retina or in- 

 ternal coat. 



The cornea is a very transparent membrane forming the 

 anterior part (about one-fifth) of the external coat of the 

 eye. Its outline is elliptical, like the opening it closes. It 

 consists, from without to within, of the following layers: 



The external layer is the conjunctival epithelium spread 

 over the outer surface of the cornea; in some animals this 



