THE EYE AND ITS VISUAL STRUCTURE. 207 



«, i. The points where the rays, having passed the cornea, con- 

 verge by the refracting power of the lens. 

 j. The cornea, or horny and transparent portion, which is 

 covered by the conjunctiva uniting different parts together. 

 The cornea fills up the vacuity which is left by the sclero- 

 tica ; but although it is closely united with it, may be 

 easily separated and will drop out. A prominent eye adds 

 greatly to the beauty of a horse, and this will depend upon 

 the projection of the cornea. But if too prominent, the 

 rays of light may be rendered too convergent, which will 

 reduce indistinct vision. If it be small and flat, the 

 rays may not be sufficiently convergent, which will produce 

 imperfect vision. An eye that is moderately convex will 

 be found best ; because, when either too prominent or too 

 flat, the horse is liable to starting and shying upon a road. 

 The cornea is quite transparent in the healthy eye, and 

 when cloudiness is observable, then it i^ an indication of 

 disease. 



In the purchase of a horse, the utmost attention should 

 be given to the condition of the cornea. Perfect trans- 

 parency over the whole surface is indispensable. The eye 

 should be carefully examined in the manner pointed out 

 at page 47 ; first in front, and afterwards through its 

 substance. 



/c, k. The crystalline, or glassy lens, situated behind the pupil and 

 in front of the vitreous humour, which is so named from a 

 supposed resemblance to melted glass ; it is a clear gela- 

 tinous fluid, very much resembling the wdiite of an egg. 

 I. The sclerotica, a hard firm coating, covering the whole of 

 the eye, except that portion occupied by the cornea, and 

 being a seeming prolongation of the covering of the optic- 

 nerve, Z, L The choroides, or choroid coat, covered with a 

 black secretion, or black or dark brown paint, called the 

 pigmentum nigrum. 



This delicate membrane extends over the whole internal 



