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A MANUAL OF VETERINARY PHYSIOLOGY 



of horses. The fear of an object may be immediately or 

 shortly dispelled by allowing the animal to smell and examine it. 

 The carelessness shown by some horses in jumping is corrected 

 by a sharp rap on the shins, and future judgment assisted by 

 a fall. 



Cartilago Nictitans. — The retractor muscle of the eye with- 

 draws the eyeball within the orbit, and the pressure thus pro- 

 duced within the cavity forces the cartilago nictitans forward, 

 so that it may be made to sweep nearly the whole corneal surface. 

 The reason why the cartilage is pressed forwards is due to the 

 fact that, though naturally curved, it becomes flattened and 



Fig. 171. — The Eye of the Horse. 



straightened out by the pressure caused by retraction, and this 

 shoots it forward ; when the pressure is removed, it retires through 

 its own elasticity, and becomes curved once more. On the 

 cartilage of some animals, especially the ox, is a small gland, 

 termed the Harderian ; its use is to prepare an unctuous secre- 

 tion, probably of a protective nature. Numerous glands, the 

 Meibomian, are also found in the eyelids, which furnish an oily 

 secretion, and prevent the overflow of tears. 



The Tears are secreted by the lachrymal gland, which is placed 

 on the upper surface of the eyeball ; they find their way into the 

 conjunctival sac by numerous small tubes. The tears pass 

 through the narrow fiunctum into the lachrymal duct, and so into 



