CHAPTER IX 

 DISEASES OF THE IRIS AND CILIARY BODY 



The structure of the iris is practically the same in all 

 animals, though the arrangement of the muscle-fibers 

 differ somewhat. For example, the pupil of the horse 

 is elliptic horizontally, while that of the cat has the 

 appearance of a vertical sHt during contraction. The 

 corpus nigra, suspended from the upper portion of the 

 horse's pupil, has the appearance of a pathologic tumor. 



The color depends upon the amount of pigment 

 present in the posterior layers and in the meshes. Some 

 animals — white rabbits for instance — are devoid of 

 pigment and the irides are of a pinkish color. In horses 

 this is occasionally seen as a partial defect, a portion 

 only of the iris and adjacent structure appearing white 

 or pink. It is not unusual in the human family to see 

 persons with little or no pigment in the irides, and when 

 such is the case the hair and other portions of the body 

 are lacking in this element. Such persons are known as 

 ''albinos." An unequal amount of pigment in each 

 iris causes one to look blue and the other brown or 

 black. 



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