378 



DISSECTION OF THE SPINAL CORD. 



ture in the dura mater, opposite the intervertebral foramen ; as they ap- 

 proach that aperture they are collected into two bundles (fig. 123 B, />) 

 which, lying side by side, receive a sheath from the dura mater, and enter 

 the two points of the intervertebral ganglion. 



Fig. 123. 



Plan of the origin of a spinal nerve from the spinal 



cord. 



Anterior root. 

 Posterior root. 



Ganglion on the posterior root. 

 Anterior primary banch. 

 Posterior primary branch of the nerve trunk. 



A drawing to show the arrangement of the nerve-roots, 

 and the form of the ganglion in a lumbar nerve. 



Posterior root gathered into two bundles of threads. 



The ganglion, bifid at the inner end. 



Threads of the anterior root, also gathered into two 

 bundles. 



The intervertebral ganglion (fig. 123). Each posterior root is provided 

 with a ganglion (c). The ganglia are reddish in color, and oval in shape 

 whilst they are surrounded by the dura mater ; and their size is propor- 

 tioned to that of the root. By means of the previous dissection, the gan- 

 glion may be seen to be bifid at the inner end (fig. 123 B), where it is 

 joined by the bundles of fibrils of the root (b) ; it might be said to possess 

 two small ganglia, one for each bundle of fibrils, which are blended at 

 their outer ends. 



Sometimes the first or suboccipital nerve is without a ganglion. 



The anterior or aganglionic roots (fig. 123 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 intervertebral 

 foramen, the fibrils enter a distinct opening in, and have a separate sheath 

 of the dura mater. In their further course to the trunk of the nerve they 

 are gathered into two bundles (fig. 123, B, </), and puss over the ganglion 

 without joining it. Finally the anterior root blends with the posterior 

 beyond tin- ganglion, to form the trunk. 



Characters of the roots. Besides variations in the relative size of the 

 two roots, the following characters are to be noted : 



Union of the fibrils. The fibrils of contiguous anterior roots may be 

 intermingled, and the fibrils of the neighboring posterior roots may be 

 connected in a like manner ; but the anterior is never mixed with the 

 posterior root. 



