THE SPINAL NERVE. 



757 



root ganglion, from which they can be traced into the cord in two main bundles, 

 the course of which has already been studied (page 697). 



The anterior roots are smaller than the posterior, devoid of ganglionic enlarge- 

 ment, and their component fibrils are collected into two bundles near the inter- 

 vertebral foramina. 



The posterior roots of the nerves are larger, but the individual filaments are 

 finer and more delicate than those of the anterior. As their component fibrils pass 

 outward toward the aperture in the dura mater, they coalesce into two bundles, 

 receive a tubular sheath from that membrane, and enter the ganglion which is 

 developed upon each root. 



The posterior root of the first cervical nerve forms an exception to these 

 characters. It is smaller than the anterior, has occasionally no ganglion 

 developed upon it, and when the ganglion exists, it is often situated within the 

 dura mater. 



The Ganglia of the Spinal Nerves. 



A ganglion is developed upon the posterior root of each of the spinal nerves. 

 These ganglia are of an oval form and of a reddish color : they bear a proportion 

 in size to the nerves upon which they are formed, and are placed in the inter- 

 vertebral foramina, external to the point where the nerves perforate the dura 



Neuraxis of Peripheral 

 Sensory Neurone 



Nerve Trunk 



Spinal Ganglion 



Dendrite of 



Peripheral Sensory 



Neurone 



Neuraxis of Peripheral Motor Neurone 



Sympathetic Ganglion 



Neuraxis of 

 Sympathetic Neurone 



FIG. 407. Diagram to show the composition of a peripheral nerve-trunk. (Bohm and Davidoff.) 



mater. Each ganglion is bifid internally, where it is joined by the two bundles 

 of the posterior root, the two portions being united into a single mass externally. 

 The ganglion upon the first and second cervical nerves forms an exception to these 

 characters, being placed on the arches of the vertebrae over which the nerves pass. 

 The ganglia of the sacral nerves are placed within the spinal canal ; and that on 

 the coccygeal nerve, also in the canal, is situated at some distance from the origin 

 of the posterior root. 



DISTRIBUTION OF THE SPINAL NERVES. 



Immediately beyond the ganglion the two roots coalesce, their fibres inter- 

 mingle, and the trunk thus formed constitutes the spinal nerve ; it passes out of 

 the inter vertebral foramen, and divides into a posterior division for the supply of 

 the posterior part of the body, and an anterior division for the supply of the 

 anterior part of the body, each containing fibres from both roots. 



Before dividing, each spinal nerve gives off a small recurrent or meningeal 

 branch, which is joined by a filament from the communicating branch of the 

 sympathetic, which connects the ganglion with the anterior division. It passes 

 inward through the intervertebral foramen and supplies the dura mater, sending 

 branches to the bones and ligaments. 



