-190 THE ANATOMY OF THE llOllsE 



CHAPTER XXTTT 



THE NKRVOUS SYSTKM 



rilYSlOLuGY OF THE NEKVuCS SY.SIEM— CHIEF lHVIsInNS OF THE NEIlVOrS SYSTEM— THE 

 SPINAL CORD— THE MEDULLA OBLONOATA — 1 HK F.NCEl'iJALOX — THE SYMI'ATUETIO 



SY'JTEM. 



PHYSIOLOGY OF THE NERVOUS SYSTEM 



HiTiiEHTu we lui\o been cngageJ in exaiiiiiiiiig 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 which 

 atturd 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 

 nervous system, 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 wa}-, 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 are 

 carried on in the animal as in the ^•egetable without the necessity for any 

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

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

 does in the latter, by a species of cell-de^■clopment 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 others it is enclosed within it, but in every case each has its peculiar 

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

 ganglion, whatever its shape may Ije ; but 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 



Ik the house, as in all the vcrtcbrata, the nervous S3'stem is made up 

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

 what are called the retlex actions of the organs of locomotion, etc., and >vliicl) 



