490 THE ANATOMY OF THE HORSE 



CHAPTER XXIII 



THE XERVOUS SYSTEM 



PHYSIOLOGY OF THE NEllVOUS SYSTEM— CHIEF DIVISIONS OF THE NERVOUS SYSTEM— THE 

 SPINAL COKD— THE MEDULLA OBLONGATA — THE ENCEPHALON — THE SYMPATHETIC 

 SYSTEM. 



PHYSIOLOGY OF THE NERVOUS SYSTEM 



Hitherto we have been engaged in examining into the conformation of 

 the framework of the body ; into the structure and action of the muscles, 

 ■which serve to move this framework ; and into the several organs Avhich 

 afford nourishment to the whole, and keep it sound and in good order. 

 We have now to consider the prime mover of all these several agents, the 

 uer^•ous S3'stem, which may be compared to the fuel that heats the water 

 of the steam-engine, and converts that apparently most simple and inno- 

 cent fluid into the powerful agent which is capable of developing almost 

 any amount of force. This fuel, however, is itself inactive until it is 

 endowed with life by the agency of fire ; and, in the same way, the nervous 

 system of the animal being must be provided with the living principle, of 

 whose nature we can only judge by its effects when present, and by the 

 cessation of all action when absent. There are many processes which ai-e 

 carried on in the animal as in the vegetable without the necessity for any 

 direct stimulus from a nervous centre, such as the growth of each separate 

 tissue throughout the body, which takes place in the former, just as it 

 does in the latter, by a species of cell-development and metamorphosis 

 independent of nervous energy; but though this growth is thus accom- 

 plished, yet it would soon be starved out for want of pabulum, were it 

 not for the supply of food to the stomach, which requires the mandate of 

 the nervous system for its performance, and so on with every corresponding 

 action of the body. 



The nervous system is made up of two distinct substances, one grey 

 in colour, and granular in structure, which is the seat of all nervous power ; 

 the other white and fibrous, which is the telegraph wire by which this 

 power is communicated. Sometimes the grey matter envelops the white, 

 and at othei's it is enclosed within it, but in every case each has its peculiar 

 office as above mentioned. Each collection of grey matter is called a 

 ganglion, whatever its shape may be ; Ijut the white fibres may be either 

 in the form of commissures for connecting the ganglia together, or they 

 may be agents for communicating with other organs, and are then called 

 nerves. 



CHIEF DIVISIONS OF THE NERVOUS SYSTEM 



In the horse, as in all the vertebrata, the nervous system is made up 

 of the following parts. 1st. The ganglia, Avhich are intended to subserve 

 what are called the lellex actions of the organs of locomotion, etc., and which 



