NERVOUS SYSTEM. 



■n 



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. 

 m 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 (radi.x 

 posterior) (Fi^s. 133, 135, and 136, a) 

 begins as a number (twelve or more) 

 of separate nerve-bundles which emerge 

 from the posterior lateral groo\'e. 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. 



The ventral root (radix anterior) 

 (Fig 135, i') 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 

 the junction of the ventral and dorsal 



Pig. i36.^c\viZ. Portion ''^ots is one of the Spinal nerves. 



OK TH1-: SriNAL CoKi). The direction in which the nerves 



A lumhar enlargement; B, jg^^g ^j^^ ^^^.^ varies. In the cervical 



Cauda eqmiia; c, tiluin ternii- 



nale; 5^7, liftii to seventh lum- region (Fig. 1 33) and cranial part of 



bar nerves. /-///. the tliree it 1 u • -i. • 1 1 ^ j 



sacral nerves. .. dorsal roots; ^I^e lumbar region it IS nearly laterad ; 

 fi, spinal ganglia; r, dorsal at the cervical and lumbar enlargements 



rami; </, ventral rami. 



B 



