IS General Principles of Veterinary Medicine. 



THE BRAIIT AND NERVOUS SYSTEM. 



The cavity of the skull is filled with the brain, which is 

 the organ of intelligence, of voluntary motion, and of the 

 senses. The impressions on the senses are conveyed to the 

 brain by the nerves, delicate branches of which are found in 

 every part of the body. These branches unite and increase 

 in size as we follow them up, until they reach what may be 

 called the parent stem, which is the spinal cord, occupying 

 the cavity in the backbone. This is attached to the brain 

 at its base, so that every nerve fibre connects directly with 

 the brain itself. 



The nerves of sight, of hearing, of taste and smell are- 

 adapted to convey the impressions of these senses only. 



In addition to this chief system of nerves, called the 

 " cerebro-spinal ^' system, there is a lesser one, known as the 

 '' sympathetic " nerve system, which is distributed chiefly to 

 the deep lying organs in the chest and abdomen, and to the 

 blood-vessels. It is supposed to control the involuntary 

 motions of those organs. 



The brain of the horse is small for his weight and the 

 size of his head, weighing about thirty ounces, which is less 

 than the smallest sized adult brain in man ; while the brain 

 of the ox is still less, weighing about one-half that of the horse. 



As it is so much less active an organ in the lower ani- 

 mals, it is much less apt to become diseased than in the 

 human race. When its surfaces become inflamed, it leads to 

 " mad staggers," a sort of delirium ; and when with this the 

 spinal cord is attacked, the disease is that fatal and epidemic 

 one known as " cerebro-spinal meningitis." Pressure of 

 blood on the brain either by overfilling of the blood-vessels 

 or by their bursting produces a stupid dull condition, passing 

 at times into complete unconsciousness, as we witness in 

 *' sleepy staggers," sunstroke and apoplexy. 



