NERVOUS SYSTEM. 



foramen, the second leaves between the 

 arches of the atlas and axis, while all 

 the others leave the vertebral canal by 

 way of the intervertebral foramina. 

 Each nerve arises from the cord by a 

 dorsal and a ventral root. The dorsal 

 root is chiefly sensory, the ventral motor 

 in character. The dorsal root (radix 

 posterior) (Figs. 133, 135, and 136, a) 

 begins as a number (twelve or more) 

 of separate nerve-bundles which emerge 

 from the posterior lateral groove. These 

 roots lie nearly in a single plane and 

 pass laterad, converging to penetrate a 

 ganglion, the spinal ganglion (/>) (or 

 ganglion of the posterior root). All 

 the spinal ganglia except the first 

 and second are situated in the inter- 

 vertebral foramina or within the verte- 

 bral canal. The first and second are 

 situated among the muscles surrounding 

 the place of exit of the nerves. 



P The ventral root (radix anterior) 



(Fig 1 35, *") arises as a larger number of 

 small fibre-bundles which do not lie in 

 a single plane, so that in a transverse 

 section several rootlets may appear in a 

 single section. . The rootlets converge 

 to form a single mass which joins the 

 dorsal root just as it emerges from the 

 spinal ganglion. The nerve formed by 



si the junction of the ventral and dorsal 



FIG. I 3 6.-CAUIML PORTION roots is one of the S P inal nerves ' 



OF THE SPINAL CORD. The direction in which the nerves 



A lumbar enlargement; B, j eave ^ CQr( j var j es . J n the cervical 

 cauda equma; C, nlum termi- 

 nate; 5-7, fifth to seventh mm- region (Fig. 133) and cranial part of 



6, spinal ganglia; c 



rami; d, ventral rami. 



region it is nearly laterad; 

 dorsal at the cervical and lumbar enlargements 



