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CHAPTER XVII. 



Diseases of tub Eyes. 



sketch of the anatomy of the eye simple ophthalmia periodic 



ophthalmia, or moon blindness cataract turning in of the 



eyelashes worm in the eye worms under the eyelids 



amaurosis, or glass eye. 



Sketch of the Anatomy of the Eye. 



The surface of the eye (Fig. 140), and the inside of the eyelids is covered by 

 the conjunctiva, which is a delicate raucous membrane. The front of the eye- 

 ball consists of a strong transparent structure, the cornea, which is somewhat 

 of the form of a small watch-glass ; and the remainder of the part consists of a 

 strong fibrous coat, the sclerotica, which is lined by a dark membrane, the 

 choroid. Behind the cornea, and attached to the choroid, hangs a thin 

 contractile curtain, termed the iris, through the centre of which there is an 

 elliptical opening known as the pupil of the eye. The anterior portion of 

 the sclerotica lies immediately under the so-called white of the eye, which is 

 the expansion of the tendons of muscles that move the eye. We may regard 

 the cornea as the continuation of the sclerotica ; and the iris, as that of the 

 choroid. 



The pupil is dilat-ed by means of radiating muscular fibres which are in the 

 iris ; and is closed by circular fibres placed round the margin of the opening. 

 The distinctive colour of the eye is derived from that of the iris, which " is 

 variously coloured, but in the horse is brown, with more or less of a yellow 

 tinge ; sometimes, however, it is almost white or grey, when the animal is 

 said to be ' wall-eyed' " {Strangeways). Behind the iris, which is slightly 

 convex, and suspended from the choroid, is a biconvex, transparent, solid body 

 — the crystalline lens — which is compared by Chauveau to a rose diamond. 

 The lens divides the eye into two compartments ; the anterior, which is 

 partially divided by the iris, and filled by a watery fluid called the aqueous 

 humour; and the posterior which holds a very similar, but denser, liquid — the 

 vitreous humour. The crystalline lens is covered by a transparent membrane 

 called the capsule. 



The optic nerve, proceeding from the brain, enters the eyeball at its posterior 

 part, and pierces the sclerotica and choroid, and by its expansion, forms a 

 membrane, th.Q retina, which lines the choroid, and terminates at the circum- 

 ference of the crystalline lens. When rays of light, coming from any object, 

 fall on the eye, they enter the pupil, and passing through the crystalline lens, 

 form an image on the retina, which conveys, through the optic nerve to the 

 brain, an impression of the object seen. This optical apparatus differs from 



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