588 



THE NERVOUS SYSTEM 



surrounding the cord; and directly after their emergence, where the roots lie 

 in the intervertebral foramen, a ganglion is found on the posterior root. The 

 anterior root lies in contact with the anterior surface of the ganglion, but none 

 of its fibers intermingle with those in the ganglion, figure 361. But imme- 

 diately beyond the ganglion the two roots coalesce, and by the mingling of 

 their fibers form a mixed spinal nerve; the spinal nerve, after issuing from 

 the intervertebral canal, gives off anterior and posterior (or ventral and dorsal) 

 branches, each containing fibers from both the roots. A third or visceral 

 branch of the spinal nerve, ramus communicans, joins the sympathetic 

 chain. 



The anterior root of each spinal nerve arises by numerous separate and 



Entering posterior 

 root 



Lissauer's tract 



anterior root 



FIG. 364. Diagrammatic Transverse Section of the Spinal Cord, Showing the Conduction 

 Paths and Groups of Cells. (Cunningham.) 



converging bundles from the anterior columns of the cord; the posterior root 

 by more numerous parallel bundles, from the posterior column. The 

 anterior roots of each spinal nerve consist chiefly of efferent fibers; the pos- 

 terior exclusively of afferent fibers. 



Course of the Fibers of the Spinal Nerve Roots. The Anterior 

 Roots. The anterior roots leave the cord in several bundles, which may be 

 called: i, Internal; 2, Middle; 3, External. All have their origin from the 

 groups of multipolar cells in the anterior columns. The internal fibers are 

 originated partly in the internal group of nerve cells of the anterior columns 



