202 EQUINE PHYSIOLOGY. 



and cones being the most sensitive portion. The point of en- 

 trance of the optic nerve is known as the blind spot. 



Accommodation. 



When an object is distant, the rays of light are more parallel, 

 less refraction is necessary, and the lens is flattened. When the 

 object is near, the opposite condition holds, the lens becoming 

 convex by contraction of the ciliary muscle ; this decreasing the 

 intra-ocular pressure and allowing the lens to increase in thick- 

 ness. In the ordinary condition the intra-ocular pressure on the 

 suspensory hgament of the lens retains it in a flattened state. 



Space need not, obviously, be given to errors of refraction and 

 accommodation. 



REPRODUCTION. 



For discussion of copulation and development of the embryo, 

 see works on Veterinary Obstetrics and Embryology. 



