ON THE EYE. 33 



This position of the eye enables him, in some 

 degree, to see behind him, and to kick against an 

 adversary with greater certainty. The anatomy 

 of the horse's eye varies, in some instances, 

 from the human eye, although the functions 

 are precisely the same. The pupil of the hu- 

 man eye is circular in its form, that of the horse 

 oblong. By this formation, the horse's eye 

 takes in objects horizontally to a much greater 

 extent than the human. 



The muscles which move the horse's eye, 

 are seven in number ; in the human eye there 

 are but six. The seventh seems to be adapted 

 for the purpose of retracting the eye within the 

 orbit, to shield it from injury, and also to sus- 

 pend it in the action of grazing. It differs also 

 from the human eye by being furnished with a 

 membrane, situated at the anterior corner {vide 

 pi. 7, /. c). This membrane is common to 

 most quadrupeds*, as well as to birds. The 



* The monkey is an exception to this rule. 



D anatomical 



