CHAPTER I. 



THE SPINAL CORD. 



SEC. 1. ON SOME FEATURES OF THE SPINAL NEBVES. 



448. WE have called the muscular and nervous tissues the 

 master tissues of the body ; but a special part of the nervous 

 system, that which we know as the central nervous system, the 

 brain and spinal cord, is supreme among the nervous tissues 

 and is master of the skeletal muscles as well as of the rest of 

 the body. We have already (Book i. Chap, in.) touched on 

 some of the general features of the nervous system, and have 

 now to study in detail the working of the brain and spinal cord. 

 We have to inquire what we know concerning the laws which 

 regulate the discharge of efferent impulses from the brain or 

 from the cord, and to learn how that discharge is determined 

 on the one hand .by intrinsic changes originating, apparently, in 

 the substance of the brain or of the cord, and on the other hand 

 by the nature and amount of the afferent impulses which reach 

 them along afferent nerves. 



As we shall see, the study of the spinal cord cannot be wholly 

 separated from that of the brain, the two being very closely 

 related. Nevertheless it will be of advantage to deal with the 

 spinal cord by itself as far as we can. The medulla oblongata 

 or spinal bulb 1 we shall consider as part of the brain. But 

 before we speak of the spinal cord itself, it will be desirable to 

 say a few words concerning the spinal nerves, that is to say the 

 nerves which issue from the spinal cord. 



We have already seen ( 88) that each of the spinal nerves 

 arises by two roots, an anterior root attached to the ventral or 



1 The term medulla oblongata is not only long, but presents difficulties, 

 since the word medulla is now rarely used to denote the whole spinal cord (me- 

 dulla spinalis) but is generally used to denote the peculiar coat of a nerve fibre, 

 the white substance of Schwann. In using instead the word bulb or if neces- 

 sary, spinal bulb there is little fear of confusion with any other kind of bulb. 

 The adjective is in not uncommon use, in such phrases as ' bulbar paralysis.' 



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