52 ELEMENTS OF HIPPOLOGY. 



the crystalline lens. In front of the anterior chamber is tha 

 cornea. The cornea, crystalline lens, and the two humors, are 

 perfectly transparent in the healthy eye. The crystalline lens 

 is screened by the iris, a sensitive membrane that is pierced 

 at its center by the pupil. The iris is capable of expanding and 

 contracting, and so can regulate the supply of light admitted to 

 the retina through the pupil. 



Looking closely into the sound eye, a fringe of sooty, spongy 

 aspect will be seen, attached to the edge of the iris, heavier above 

 than below. It is called the corpora nigra, and is a provision 

 of Nature to partially absorb the light entering the eye and to 

 supply the protection given to the human eye by the overhanging 

 eyebrow. 



The pupils should dilate and contract equally and freely, 

 The iris should be of uniform color. Frequently there is lack of 

 color in the iris. The visible effeo-ts of this condition is the 

 whitish ring surrounding the pupil, known as wall-eye. 



An opacity of the cornea is a positive defect that limits the' 

 field of vision of the horse. Such a horse is usually a shyer, 

 nervous and undesirable for any sort of fast work. 



The wall-eyed horse must not be confused with the horse 

 that "shows the white of his eye," already discussed. In the 

 ordinary case the white does not show, but an excitable, nervous 

 horse, suffering from timidity or fear, will open his eyes unduly 

 wide and so show the whites of them. It is a sign of nervousness 

 or vice, or both, and, while often merely the result of brutal 

 treatment, is always an undesirable quality. 



As a protection to the eye, to remove foreign particles that 

 adhere to its outer surface. Nature provides the haw, a thin mem- 

 brane that, in a restful state, appears as a thin fold at the inner 

 angle of the eye. When the eye is irritated by dust, hail, chaff, 

 or the like, the ball is slightly withdrawn into the socket and the 

 haw is stretched across the eye, removmg mechanically the ir- 

 ritant, assisted by a profuse flow of tears. 



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