VETERINARY OPHTHALMOLOGY. 7 



we have resulting — vision. Vision in all animals de- 

 pends on the sensibility of the retina (optic nerve 

 filaments) to the vibration of luminous rays. The 

 amount of light admitted to the eye is regulated by a 

 curtain, the iris, the movements of which are reflex. 

 The eye adjusts itself (accommodation) for distances, so 

 that the retina is properly focussed for distance and 

 for objects near by. (Fig. 2.) At the base of the 

 horse's eye is found a collection of pigment cells — bril- 

 liant — called the tapetum, and in a darkened stall one 

 may get the reflex from the eye, bluish in coloi-, more 

 of a yellow in the ox and reddish-yellow in the cat. 



In the horse the eyes are placed in their orbits in- 

 clined toward the sides. Only a portion of a view is 



Fig. 8. 



perfectly appreciated at one time, the surrounding 

 being less and less distinct, but from the perfect action 



