ANATOMY, UNSOUNDNESS, AND AGE OF A HORSE 4I 



tines. Into the caecum is passed much of the undigested 

 matter, together with the digestive agencies of the small 

 intestine. Here the digestive processes are prolonged, 

 thus compensating, in part at least, for the small capacity 

 of the horse's stomach. 



Capacity and Length of the Horse's Stomacij and 

 Intestines, Compared With That of the Cow, Sheep 

 AND Hog. 



Nervous system. — This system consists of the brain, 

 spinal and sympathetic ganglia, and nerves. The dif- 

 ferent organs of this system are composed of two struc- 

 tures, the vesicular or gray matter and the fibrous or 

 white matter. The nervous substance presents two dis- 

 tinct forms — nerve cells and nerve fibers. The nerves 

 arise from the cerebro-spinal axis and, branching as they 

 go, are distributed to all parts of the body. Every organ 

 and tissue has its supply of nerves connecting it with 

 the brain or spinal cord. (Fig. 23.) 



The nervous system of the horse is the power which 

 stimulates and directs the action of his muscles, and is the 

 source of his mental capacity. In general, the amount of 

 contraction force exhibited by a muscle is proportionate 

 to the degree of stimulation given by its nerves. In con- 

 sidering the form of the horse from a mechanical point 

 of view, we must not lose sight of the marked difference 

 which exists in the nervous system of various animals. 



