COURSE OF THE FIBERS OF THE SPINAL NERVE ROOTS 



517 



the cord; and directly after their emergence, where the roots lie in the inter- 

 vertebral 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 immediately 

 beyond the ganglion the two roots coalesce, and by the mingling of their fibers 

 form a compound or mixed spinal nerve, which, after issuing from the inter- 

 vertebral canal, gives off anterior and posterior (or ventral and dorsal) branches, 

 each containing fibers from both the roots as well as a third or visceral 

 branch, ramus communicans, to the sympathetic. 



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

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



Entering posterior 

 root 



Lissauer's tract 



Emc 



; anterior root 



FIG. 362. Diagrammatic Transverse Section of the Spinal Cord, Showing the Conduction Paths 

 and Groups of Cells. (Cunningham.) 



by more numerous parallel bundles, from the posterior column, or, rather, 

 from the posterior part of the lateral column, for if a fissure be directed 

 inward from the groove between the middle and posterior columns, the pos- 

 terior roots will remain attached to the former. The anterior roots of each 

 spinal nerve consist chiefly of efferent fibers; the posterior 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 cornua. The internal fibers are 

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



