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CHAPTER XI. 



OF THE SPINAL NERVES. OF THE ENCEPHALIC NERVES. METIK 



OF DETERMINING THE FUNCTIONS OF NERVES. OF THE FUN< 



TIONS OF THE SPINAL CORD AND ENCEPHALON. 



BEFORE we can satisfactorily investigate the functions of the cei 

 bro-spinal centre, or of its various segments, it will be necessary to 

 give some account of the nerves which are connected with them. 



These nerves are described in two classes, the spinal and the en- 

 cephalic. The former class consists of all those which arise from 

 the spinal cord, and emerge from the spinal canal through orifices 

 in its wall. The latter consists of those which are connected with 

 the encephalon. 



Of the Spinal Nerves. There is a pair of spinal nerves for each 

 pair of intervertebral foramina on the same level, and for those be- 

 tween the atlas and occiput. We can thus enumerate in all thirty- 

 one pair of nerves having their origin from the spinal cord, exclusive 

 of the spinal accessory nerve, which is connected with the upper 

 part of the cervical region. 



The spinal nerves have the following very constant characters. 

 Each has its origin by two roots, of which the anterior is distinctly 

 inferior in size to the posterior (fig. 61, p, a, p. 222). The ligamen- 

 tum denticulatum is placed between these roots. Each root passes 

 out by a distinct opening in the dura mater. Immediately after 

 its emergence a ganglion is formed on the posterior root, and the 

 anterior root lies imbedded in the anterior surface of the ganglion, 

 and inclosed in the same sheath, but without mingling its fibres 

 with those of the ganglion. Beyond it, the nervous fibres of both 

 roots intermingle, and a compound spinal nerve results. The trunk 

 thus formed passes immediately through the intervertebral canal, 

 and divides into an anterior and posterior branch (fig. 61, ', p')> 

 The former is in general considerably the larger. The latter passes 

 backwards, and sinks in among the muscles of the posterior regions 

 of the trunk. The anterior branches in the cervical, lumbar, and 

 sacral regions form large and intricate plexuses, (cervical, axillary, 



