MUSCLES AND PARTS COI^NECTED AVITH THE EYE. 201 



z. The superior portion of the parotid gland, or gland situate 

 near the ear, reversed to exhibit the blood-vessels and nerves 

 beneath it. 



MUSCLES AND PARTS CONNECTED WITH THE EYE. 



PLATE III. Fig. 4 and 5. 



The horse has a very extended field of vision. The eye 

 is provided with seven muscles to move it in all directions ; 

 and that they may act with sufficient promptitude and power, 

 no fewer than six nerves are directed to the eye generally, 

 or to particular muscles ; and that it may receive no injury 

 from friction, it rests upon a mass of fatty matter, which 

 also enables it to be turned without much exertion of the 

 muscles. Four of the muscles, a, e, and d, are straight ; 

 these rise from the back of the orbit, and are inserted into 

 the ball of the eye, immediately opposite, and at equal 

 distances from each other. One of these, /, rises to the 

 upper part of the eye, immediately behind the , transparent 

 and visible portion of it, the office of which is to raise the 

 eye. When it contracts, the eye must necessarily be drawn 

 upward. Another, a, is inserted immediately opposite, at 

 the bottom of the eye, for the purpose of depressing the eye, 

 or enabling the horse to look downwards. A third, e, is 

 inserted at the outer corner, which turns the eye outward ; 

 and a fourth is inserted at the inner corner for turning the 

 eye inwards. By means of all these the eye can rotate, 

 or be turned in any direction at the will of the animal. 

 Should the animal wish to look upward and outward, then 

 the outer and upper muscles are called into action, and can 

 be modified in any manner at the will of the horse. These 

 muscles perform another duty, namely, keeping the eye in 

 its place, for while grazing the principal weight of the 

 eye rests upon them ; and to aid them in this, another 



2 D 



