THE SPIRAL SERVE*. 



827 



Ganglia of the Spinal Nerves. 



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

 These cranglia 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 interver- 

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

 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, also, of the sacral nerves are placed within the spinal canal ; and 

 that on the coccygeal nerve, also in the canal, about the middle of its posterior root. 



DISTRIBUTION OF THE SPINAL XERYES. 



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

 mingle, and the trunk thus formed passes out of the intervertebral 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 con- 

 taining fibres from both roots. Before division each trunk gives off a recurrent 

 branch to the dura mater of the cord. 



The posterior divisions of the spinal nerves are generally smaller than the 

 anterior ; they arise from the trunk resulting from the union of the roots in 

 the intravertebral foramina, and, passing backward, divide into internal and 

 external branches, which are distributed to the muscles and integument behind 

 the spine. The first cervical, the fourth and fifth sacral, and the coccygeal 

 nerves are exceptions to these characters. 



The anterior divisions of the spinal nerves supply the parts of the body in front 

 of the spine, including the limbs. They are for the most part larger than the 

 posterior divisions. Each division is connected Avith the sympathetic by slender 

 filaments from which a communicating branch runs to the recurrent filament from 

 the trunk. In the dorsal region the anterior divisions of the spinal nerves are 

 completely separate from each other, and are uniform in their distribution ; but 

 in the cervical, lumbar, and sacral regions they form intricate plexuses previous 

 to their distribution. 



Points of Emergence of the Spinal Nerves. 



The roots of the spinal nerves from their origin in the cord run obliquely 

 downward to their point of exit from the intervertebral foramina, the amount of 

 obliquity varying in different regions of the spine, and being greater in the lower 

 than the upper part. The level of their emergence from the cord is within certain 



