THE SPINAL NERVES 



693 



The ganglia vary greatly in size; that of the first cervical nerve is scarcely as large as a hemp- 

 seed, while that of the eightli cervical is al)Out 2 cm. long and 1 cm. wide. On the large roots 

 connected with the cervical and lumbar enlargement of the cord there are multiple ganglia of 

 varying sizes interpo.sed in the cour.se of the root-hundles. The fil)(>rs of the dorsal roots arise 

 from the cells of the spinal ganglia; each cell gives oif a fiber which ent(M's tlie spinal cord and 

 another which passes into the nerve. 



The ventral (or inferior) root (Radix ventralis) contains fewer fibers than the 

 dorsal root, except in the case of the first cervical nerve. It arises from the ventral 

 surface of the spinal cord (Fig. 495) by means of numerous small bundles of 

 fibers which do not form a linear series but emerge from the cord over an area 

 three to five millimeters in width (ventral root zone). The fibers are processes of 

 the large cells of the ventral gray colunms of the spinal cord. There is no gang- 

 lion on the ventral root. 



In the cervical, thoracic, and anterior lumbar regions the Inmdles of both roots pass through 

 separate openings in linear series in the dura mater before uniting into a root proper. Further 

 back the bundles of each root unite within the dura. In the anterior part of the cervical region 

 and in the thoracic part of the cord there are intervals of varying length between adjacent roots, 

 but in some places the fibers of adjacent roots overlap and an exchange of fibers may be observed. 



iSpinal branch of inlercostal artery 



Spinal ganglion 



Dura mater 



Lig. deiiticulatiim 



or sal roof bandies 



Superior conimon ligament 



Conjugal lignnient 

 Fig. 519. — Vertebral Canal Opened by Sawing off the Arches. (After Schmaltz, .\tlas d. Anat. d. Pferdes.) 



Many of the roots are directed almost straight outward or incline slightly backward, but the pos- 

 terior lumbar, sacral, and coccygeal roots and nerves run backward to reach the foramina through 

 which they emerge. The distance thus to be traversed increases from l)cfore backward, so that 

 these nerves form a tapering sheaf around the conus medullaris antl filum terminale in the last 

 lumbar vertebra and tlie sacrum which is known as the cauda equina. 



The size of the spinal nerves varies greatly. The largest are connected with 

 the cervical and lumbar enlargements. 



In or immediately after its emergence from the intervertebral foramen each 

 spinal nerve gives off a small meningeal or recurrent branch (Ramus meningeus). 

 This is joined by a bundle of fibers from the ramus communicans and enters the 

 verteljral canal, in which it is distributed. Each nerve then divides into two pri- 

 mary branches, dorsal and ventral (Ramus dorsalis, ventralis). The dorsal 

 branches are smaller than the ventral, except in the cervical region. They are 

 distrihutod chiefly to the muscles and skin of the dorsal part of the body. The 

 ventral branches supply in general the muscles and skin of the ventral parts of the 

 body, including the limbs. Each nerve or its ventral branch is connected with an 

 adjacent ganglion of the sympathetic system ])y at least one small short branch 

 known as a ramus communicans. Many nerves have two and some have three 



