GANGLIA CERVICAL NERVES. 633 



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 pro- 

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

 intervertebral foramina, external to the point where the nerves perforate the 

 dura rnater. 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 ex- 

 ception 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. Immediately 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. 



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 ex- 

 tent 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 ; but in the cervical, lumbar, and sacral regions, 

 they form intricate plexuses previous to 'their distribution. 



The posterior branches of the spinal nerves are generally smaller than the an- 

 terior ; they arise from the trunk, resulting from the union of the roots in the 

 intervertebral foramina, and, passing backwards, divide into external and in- 

 ternal 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, the roots of the cervical are less oblique than those of the other spinal 

 nerves. The first cervical nerve 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 be- 

 tween the posterior arch of the atlas and the lamina of the axis; and the eighth 

 (the last), between the last cervical and first dorsal vertebrae. 



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

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

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

 vical nerves, together with the first dorsal, form the brachial plexus. 



ANTERIOR BRANCHES OF THE CERVICAL NERVES. 



The anterior branch of the first, or suboccipital nerve, is of small size. It escapes 

 from the spinal canal, through a groove upon the posterior arch of the atlas. 

 In this groove it lies beneath the vertebral artery, to the inner side of the Rec- 



