f>4 THE EYE. 



power of the lens, would render vision confused or imperfect 

 These folds of the choroides are called the ciliary jyi'ocesses. 



Within the cornea, and occupying the fore-part of the eye, is 

 the aqueous hirnior, j)^ so termed from its resemblance to pure 

 water. It is that by which the cornea is preserved in its protu- 

 berant and rounded form. It extends to the crystalline lens q, 

 and therefore a portion of it, although a very small one, is be- 

 hind the iris {tn, Fig. 7). Floating in this fluid is a membrane, 

 with an oblong aperture, called the Iris. It is that which gives 

 color to the eye. The color varies little in the horse, except 

 that it always bears some analogy to that of the skin. We 

 rarely see it lighter than a hazel, or darker than a brown. 

 Horses perfectly white, or cream-colored, have the iris white 

 and the pupil red. When horses of other colors, and that are 

 usually pied, have a white iris and a black pupil, they are said 

 to be ivall-eyed. Vulgar opinion has decided that a wall-eyed 

 horse is never subject to blindness, but this is altogether erroneous. 



The aperture in the iris is termed the 'pupil, and through it 

 light passes to the inner chamber of the eye. The pupil is ob- 

 long, and variable in size. It differs with the intensity or de- 

 gree of light that falls upon the eye. 



This alteration of form in the pupil is effected by the muscu- 

 lar fibres that enter into the composition of the iris. When 

 these fibres are relaxed, the pupil must proportionably diminish. 



This dilatation or contraction of the pupil gives a useful method 

 of ascertaining the existence of blindness in one eye or in both. 

 The cornea and crystalline lens remain perfectly transparent, but 

 the retina is palsied, and is not affected by light ; and many 

 persons have been deceived when blindness of this description 

 has been confined to one eye. A horse blind in both eyes will 

 usually have his ears in constant and rapid motion, directing 

 them in quick succession to every quarter. He M'ill likcAvisc 

 hang back in his halter in a peculiar way, and will lift his feet 

 high as if he were stepping over some obstacle, when there is 

 actually nothing to obstruct his passage, and there will be an 

 evident uncertainty in the putting down of his feet. In blind- 

 ness of one eye, little or nothing of this characteristic gait and 

 manner can be perceived. Although a one-eyed horse may not 

 be absolutely condemned for the common business of the car- 

 nage or the road, he is generally deteriorated as a hunter, for he 

 cannot measure his distance, and will run into his leaps. 



Let the size of both pupils be carefully noticed before the 

 \orse is removed from the stable, and, as he is led to the door, 

 observe whether they both contract, and equally so, with the 

 increase of light. If the horse should be first seen in the o])e;i 

 air, let it be observed whether the pupils are precisely of the same 



