PHYSIOLOGY. 



31 



The veins generally accompany the arteries ; but as the 

 former are subject to pressure from the muscles, they are 

 more numerous than arteries. The veins are provided with 

 valves, which appear to be a duplicature of their inner coat 

 rising into a fold. In the human subject, there are two of 

 these folds to form a valve j but in the horse, there are three : 

 these, when the blood by pressure, or a contraction of the 

 capillary structure, is arrested in its course, prevent it from 

 returning. 



The arteries are vessels that carry the blood to all parts 

 of the system, for the purpose of supplying the waste that is 

 continually going on. They become narrower as they pro- 

 ceed towards the extremities, and are furnished with an elastic, 

 a muscular, and a membranous coat. Arteries have a pulsat- 

 ing motion communicated to them by the impulse of the 

 heart, by which they are distinguished from veins. 



The viscera are certain organs, comprising a great part of 

 the structure of the animal, ordinarily lodged in cavities, as 

 in the head, the chest, the pelvis, and abdomen. 



The head contains the brain, from which issue the organs 

 of taste, smell, hearing, sight, &c. The chest is bounded by 

 the ribs, spinal column, breast bone, and diaphragm, called 

 midriff. It contains the organs of respiration and circula- 

 tion. The abdomen contains the organs of digestion. The 

 pelvis contains the urinary organs, the rectum, and most of 

 the organs of generation. 



PHYSIOLOGY. 



DESCRIPTION OF THE USES OF THE DIFFERENT ORGANS AND 

 FUNCTIONS OF THE HORSE. 



Nutrition. — The living body is constantly losing its con- 

 stituent parts ; this waste requires to be made up by the 

 addition of new matter ; and when the stomach, and other 

 parts concerned in the process of nutrition and digestion, ar<* 



