338 NERVOUS SYSTEM. 
4 | . Ls foramen, the second leaves between the 
\ gq arches of the atlas and axis, while all 
the others leave the vertebral canal by 
ia way of the intervertebral foramina. 
Hy tf i ’ Each nerve arises from the cord by a 
Banh dorsal and a ventral root. The dorsal 
‘I | \ root is chiefly sensory, the ventral motor 
| | \ 6 in character. The dorsal root (radix 
posterior) (Figs. 133, 135, and 136, a) 
Vi begins as a number (twelve or more) 
tN of separate nerve-bundles which emerge 
\ ¢ from the posterior lateral groove. These 
Mt roots lie nearly in a single plane and 
HE \s----7 pass laterad, converging to penetrate a 
| \ ganglion, the spinal ganglion (4) (or 
VF ganglion of the posterior root). All 
cee the spinal ganglia except the first 
MN and second are situated in the inter- 
vertebral foramina or within the verte- 
poll bral canal. The first and second are 
situated among the muscles surrounding 
the place of exit of the nerves. 
“2B The ventral root (radix anterior) 
(Fig 135, ¢) arises as a larger number of 
small fibre-bundles which do not lie in 
i) a single plane, so that in a transverse 
! section several rootlets may appear ina 
| ‘single section. The rootlets converge 
| to forma single mass which joins the 
’ | dorsal root just as it emerges from the 
| spinal ganglion. The nerve formed by 
| at the junction of the ventral and dorsal 
Fic. 136.—Caupan Portion TOOts is one of the spinal nerves. 
OF THE SPINAL’ CorD. The direction in which the nerves 
A, lumbar enlargement; 3, leave the cord varies. In the cervical 
cauda equina; C, filum termi- 
nale; 5-7, fifth to seventh lum- region (Fig. 133) and. cranial part of 
bar nerves. /-///, the three the lumbar region it is nearly laterad; 
sacral nerves. @, dorsal roots; : 
6, spinal ganglia; ¢, dorsal at the cervical and lumbar enlargements 
rami; @, ventral rami. 
