5G2 SPINAL NERVES. 



GANGLIA OF THE SPINAL NERVES. 



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

 These ganglia are of an oval form, of a reddish color, bear a proportion in size 

 to the nerves upon which they are formed, and are placed in the intervertebral 

 foramina, external to the point wh^re 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 ganglia 

 upon the first and second cervical nerves form an exception to these characters, 

 being placed on the arches of the vertebras over which they 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. Imme- 

 diately beyond the ganglion, the two roots coalesce, their fibres intermingle, and 

 the trunk thus formed passes out of the intervertebral foramen, and divides into an 

 anterior branch for the supply of the anterior part of the body, and a posterior 

 branch for the posterior part, each branch containing fibres from both roots. 



ANTERIOR BRANCHES OF THE SPINAL NERVES. 



The anterior branches 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 branches ; this increase of size being proportioned to the larger extent 

 of structures they are required to supply. Each branch is connected by slender 

 filaments with the sympathetic. In the dorsal region, the anterior branches of 

 the spinal nerves are completely separate from each other, and are uniform in 

 their distribution ; bat in the cervical, lumbar, and sacral regions, they form in- 

 tricate plexuses previous to their distribution. 



POSTERIOR BRANCHES OF THE SPINAL NERVES. 



The posterior branches of the spinal nerves are generally smaller than the anterior, 

 they arise from the trunk resulting from the union of the nerves in the interverte- 

 bral foramina, and, passing backwards, divide into external and internal branches, 

 which are distributed to the muscles and integument behind the spine. The first 

 cervical and lower sacral nerves are exceptions to these characters. 



CERVICAL NERVES. 



The roots of the cervical nerves increase in size from the first to the fifth, and 

 then maintain the same size to the eighth. The posterior roots bear a proportion 

 to the anterior as 3' to 1, which is much greater than in any other region ; the 

 individual filaments being also much larger than those of the anterior roots. In 

 direction, they are less oblique than those of the other spinal nerves. The first 

 is directed a little upwards and outwards ; the second is horizontal ; the others 

 are directed obliquely downwards and outwards, the lowest being the most oblique, 

 and consequently longer than the upper, the distance between their place of origin 

 and their point of exit from the spinal canal never exceeding the depth of one 

 vertebra. 



The trunk of the first cervical nerve (suboccipital), leaves the spinal canal, between 

 the occipital bone and the posterior arch of the atlas; the second between the 

 posterior arch of the atlas and the lamina of the axis ; and the eighth (the last), 

 between the last cervical and first dorsal vertebras. 



Each nerve, at its exit from the intervertebral foramen, divides into an anterior 

 and a posterior branch. The anterior branches of the four upper cervical nerves 

 form the cervical plexus. The anterior branches of the four lower cervical nerves, 

 together with the first dorsal, form the brachial plexus. 



