THE NERVOUS SYSTEM. 265 



in a very imperfect manner) presides over and keeps going the 

 other systems — circulatory, digestive, respiratory, etc. — and that 

 without it the whole organism would come to a standstill; the im- 

 pression undoubtedly prevails in the minds of leading veterinarians 

 that primary disease of the brain, the spinal cord and the nerves, 

 is comparatively rare in the horse, and probably this is so; seeing 

 the diflSculties in the way of recognizing the various morbid con- 

 ditions in the human subject, and hence the greater difficulties 

 that must of necessit}^ beset the veterinarian to discern similar 

 conditions among the lower animals, it is a matter of congratula- 

 tion that diseases of the nervous system are comparative! 3' rare 

 among our patients; nevertheless we fully believe that the entire 

 dependence of the other systems upon the nerves warrants the 

 conviction that the study of the influence exerted by the nervous 

 system as a factor in the cause of disease among horses and lower 

 animals generally, demands far more serious consideration than it 

 has 5'et received. 



Before proceeding to the consideration of the diseases affecting 

 the different parts of the nervous system, it is desirable for the 

 sake of simplicity and the clearer appreciation of the same, 

 that an explanation should be given of the parts that enter 

 into the composition of this intricate and highly important 

 division of animal life. The apparatus which provides, supplies 

 and conveys all over the bod}- that excitation which is requisite 

 for the execution of all the acts and functions that are indispens- 

 able for the maintenance of life, is divided into two parts, namely: 

 the cerebro-spi7ial axis, which consists of the brain and spinal cord, 

 and the nerves, which are given off on either .side of the central 

 axis and therefrom distributed to all parts of the body. The 

 brain and spinal cord are both enveloped, for the sake of protec- 

 tion, in a bony case called the cranial cavity (or skull) and the 

 spinal canal (or vertebrae); in addition to these there are three 

 membranes called the meninges, which serve to separate the soft 

 nervous substance from this hard, bony case; the outer membrane 

 serves as a lining to the bony case and is called the " dura mater;'' 

 the inner membrane, which is closely adherent to the outer sur- 

 face of the cord and brain, is called the " pia mater;'' while the 

 middle membrane consists of two layers, one covering the outer 

 portion of the pia mater and the other the inner part of the dura. 



