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PHINCIPLES OP VETERINARY SCIENCE 



auditory nerve transmits the impulses to the auditory center of 

 the brain. The maintenance of equihbrium is largely centered 

 in the mechanisms of the internal ear. 



THE EYE 



The eye is the organ of vision. It comprises the eyeball, the 

 optic nerve, and the accessory structures — the eyelids, the con- 

 junctiva, and the lacrimal apparatus. 



Reflection of conjunctiva 



Optic nerve 



Optic papilla 

 Retrobulbar fat- 



Rectus oculi inferior 



Granula iridis 



Cornea 



Lens 

 A nterior chamber 



Ciliary processes 



Chorioid 



Fia. 56. — Vertical section of eyeball of horse. The contour of the crystalline 

 lens is dotted. (Sisson, Anatomy of Domestic Animals.) 



The eyelids are the most exposed parts. They are movable 

 folds of skin on the margins of which the eyelashes are borne. 

 The third eyelid, haw, or nictitating membrane is an important 

 part of the eye of the horse. It consists of a plate of cartilage 

 covered by a fold of the conjunctiva. By frequently closing and 

 opening the eyelids foreign particles are removed from the ex- 

 posed parts, thus keeping the eye in working order. 



The conjunctiva is the mucous membrane which lines the eye- 

 lids and is reflected on to the anterior part of the eyeball. It is 

 normally moist and of a bright pink color. 



The lacrimal apparatus is made up of the lacrimal gland, 

 which secretes the tears; and the lacrimal duct, which carries 



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