.J08 



A Manual of Veterinary Physiology. 



and inferior oblique muscles, the object being to bring the 

 pupillary opening as far as possible to the front. That the 

 horse succeeds in this can be readily determined by simple 

 inspection ; the inner part of the iris, as far as the edge of 

 the pupil, may often be seen in both eyes to disappear 

 beneath the folds of the eyelid, in the powerful endeavour 

 to concentrate both eyes on an object situated directly to 



Fig. 34.— The P< 



Eyes 



BlNOCULAB 



the front. In no other position has the horse binocular 

 vision (that is to say, single vision resulting from the em- 

 ployment of a pair of eyes), and to direct the rays of Light 

 into the outer half of each lens, the corpora nigra appeal 

 to be placed in the centre of the pupillary opening.* 



* The greal argument which tells against tins theory is thai rami 

 mints, which bave also binocular vision, have no corpora nigra. Their 



