THE EYE AND ITS VISUAL STRUCTURE. 
207 
i, 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 
produce 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 is 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. 
k , 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 white of an egg. 
1. 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, Z. 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 
