ROOTS OF THE NERVES. 



543 



The posterior or ganglionic roots (fig. 196, A, 6) are larger than 

 the anterior, and are formed by thicker and more numerous fibrils. 

 They are attached to the side of 

 the cord between the posterior 

 and lateral columns in a straight 

 line, which they preserve even to 

 the last nerve. 



In their course to the trunk of 

 the nerve the fibrils converge to 

 an aperture in the dura mater, 

 opposite the intervertebral fora- 

 men ; as they approach that aper- 

 ture they are collected into two 

 bundle* "(fig. 196, B, 6) which, 

 lying side by side, receive a sheath 

 from the dura mater, and enter 

 the two points of the intervertebral 

 ganglion. 



The inten'ertebral ganglion (fig. 

 196 A, c) is reddish in colour and 

 oval in shape ; and its size is pro- 

 portioned to that of the root. By 

 means of the previous dissection, 

 the ganglion may be seen to be 

 bifid at the inner end (fig. 196 B), 

 where it is joined by the bundles 

 of filaments of the root (6) ; or the 

 root might be said to possess two 

 small ganglia, one for each bundle 

 of filaments, which are blended at 

 their outer ends. 



Sometimes the first or subocci- 

 pital nerve is without a ganglion. 



The anterior or aganglionic roots 

 (fig. 196 A, a) arise from the side 

 of the spinal cord by filaments 

 which are attached irregularly 

 not in a straight line, and approach 

 near the middle fissure at the 

 lower end of the cord. 



Taking the same direction as 

 the posterior root to the inter- 

 vertebral foramen, the fibrils enter 

 a distinct opening in, and have a 

 separate sheath of, the dura mater. 

 In their farther course to the trunk 



of the nerve they are gathered into two bundles (fig. 196 B, a), 

 and pass over the ganglion without joining it. Finally, the anterior 

 root blends with the posterior beyond the ganglion, to form the 

 trunk of the nerve. 



Posterior 

 larger than 

 anterior. 



forms two 

 bundles 



that enter 

 the ganglion. 



FIG. 196. 



A. PLAN OF THE ORIGIN OP A 



SPINAL NERVE FROM THE 

 SPINAL CORD. 



a. Anterior root. 



b. Posterior root. 



c. Gangl iou on the posterior root. 



d. Anterior primary branch. 



e. Posterior primary branch of 

 the nerve-trunk. 



B. A DRAWING TO SHOW THE 



ARRANGEMENT OF THE 

 XERVK-ROOTS, AND THE FORM 

 OF THE GANGLION IN A LUM- 

 BAR NERVE. 



b, b. Posterior root gathered into 

 two bundles of threads. 



c. The ganglion, bifid at the 

 inner end. 



a, a. Filaments of the anterior 

 root, also gathered into two bundles. 



Anterior 

 root is 

 without 

 ganglion, 



pierces 

 dura mater 

 and joins 

 posterior 

 root beyond 

 ganglion. 



