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been killed, wlien the clear transparent cornea will suddenly become 

 clouded over with a whitish blue opacity, and this will remain until the 

 compression is interrupted. The interior of the eye contains three trans- 

 parent media for the refraction of the rays of light, on their way from the 

 cornea to the visual nerve. Of these media the anterior one (aqueous 

 humor) is liquid, the posterior (vitreous humor) is semi-solid, and the 

 intermediate one (crystalline lens) is solid. The space occupied by the 

 aqueous humor corresponds nearly to the portion of the eye covered by 

 the transparent cornea. It is, however, divided into two chambers, an- 

 terior and posterior, by the iris, a contractile curtain with a hole in the 

 center (the pupil), and which may be looked on as in some sense a projec- 

 tion inward of the vascular and pigmentary coat from its anterior margin 

 at the point where the sclerotic or opaque outer coat becomes continuous 

 with the cornea or transparent one. This iris, or curtain, besides its 

 abundance of blood-vessels and pigment, possesses two sets of muscular 

 fibers, one set radiating from the margin of the pupil to the outer border 

 of the curtain at its attach ment to the sclerotic and choroid, and the other 

 encircling the pupil in the manner of a ring. The action of the two sets 

 is necessarily antagonistic, the radiating fibers dilating the pupil and 

 exposing the interior of the eye to view, while the circular fibers con- 

 tract this opening and shut out the rays of light. The form of the pupil 

 in the horse is ovoid, with its longest diameter from side to side and its 

 upper border is fringed by several minute black bodies (corpora nigra) 

 projecting forward and serving to some extent the purpose of eyebrows 

 in arresting and absorbing the excess of rays of light which fall upon 

 the eye from above. These pigmentary projections in front of the upper 

 border of the pupil are often mistaken for the products of disease or in- 

 jury, in place of the normal and beneficient protectors of the nerve of 

 sight which they are. They may, like all other parts, become the seat of 

 disease, but so long as they and the iris retain their clear, dark aspect, 

 without any tints of brown or yellow, they may be held to be healthy. 



The vitreous or semi-solid refracting medium occupies the posterior 

 part of the eye— the part corresponding to the sclerotic, choroid, and 

 retina— and has a consistency corresponding to that of the white of an 

 egg, and a power of refraction of the light-rays correspondingly greater 

 than the aqueous humor. 



The third or solid refracting medium is a biconvex lens, with its con- 

 vexity greatest on its posterior surface, which is lodged in a depression 

 in the vitreous humor, while its anterior surface corresponds to the 

 opening of the pupil. It is inclosed in a membranous covering (cap- 

 sule), and is maintained in posirion by a membrane (suspensory liga- 

 ment) which extends from the margin of the lens outward to the scle- 

 rotic at the point of junction of the choroid and iris. This ligament is, 

 in its turn, furnished with radiating muscular fibers, which change the 

 form or position of the lens so as to adapt it to see with equal clearness 

 objects at a distance or close by. 



