THE NERVE SYSTEM 



POSTERIOR) 



NERVE - 

 ROOTS ) 



POSTERIOR 

 ROOTS 



ANTERIOR 

 NERVE 

 ROOTS 



LIGAMENTUM 

 DENTICULATUM 



DURA 

 'OPENED 



ANTERIOR 

 ROOTS 



SPINAL NERVE 

 IN ITS PIAL 

 SHEATH 



It will be observed that each group of nerves corresponds in number with the 

 vertebrae in that region, except the cervical and coccygeal. Sometimes there is no 

 thirty-first pair. Occasionally below the thirty-first pair there may be one or 

 even two filamentous pairs which do not pass out of the vertebral canal. 



Each spinal nerve arises by two roots, an anterior, ventral, or motor root and a 

 posterior, dorsal, or sensor root, the latter being distinguished by a ganglion termed 

 the spinal ganglion. 



The Anterior or Ventral Root (radix anterior}. The superficial origin is from 

 the antero-lateral columns of the cord, corresponding to the situation of the 

 anterior cornu of gray substance. Each root is composed of from four to eight 

 filaments. 



The deep origin can be traced from cells in the gray substance of the anterior 

 cornu of the same as well as of the opposite side. The majority of the axones 

 arise from the various groups of cells in the anterior cornu of the same side, 



while others arise from the large cells 

 of the anterior cornu of the opposite 

 side, the axones passing across the 

 median plane in the anterior white 

 commissure. The axone bundles, after 

 leaving the gray substance, penetrate 

 horizontally through the longitudinal 

 bundles of the antero-lateral column 

 to emerge as described above. 



The Posterior or Dorsal Root (radix 

 posterior). The superficial origin is by 

 filaments (fila radicularia\ from the 

 postero-lateral fissure of the cord. The 

 real origin of these fibres is from the 

 nerve cells in the posterior root gan- 

 glion, from which they can be traced 

 into the cord in two main bundles, 

 the course of which has already been 

 studied (p. 839). The posterior or 

 dorsal root of the first cervical nerve is 

 exceptional in that it is smaller than 

 the anterior; it is occasionally wanting. 

 Within the vertebral canal the nerve 

 roots are separated from each other by 

 theligamentum denticulatum (Fig. 750). 

 In the cervical region the spinal portion 

 of the spinal accessory nerve separates 

 the roots. 



The spinal ganglia are collections of 

 nerve cells on the posterior root of each 

 of the spinal nerves. Each ganglion is oval in shape and of a reddish color; 

 and its size bears a proportion to that of the nerve root upon which it is situated; it 

 is bifid internally where it is joined by the two bundles of the posterior nerve root. 

 The ganglia afe usually placed in the intervertebral foramina, ectad of the point 

 where the nerves perforate the dura. There are, however, exceptions to this 

 rule. Thus, the ganglia upon the first and second cervical nerves lie on the neural 

 arches of the atlas and axis respectively; those of the sacral nerves are placed 

 within the vertebral canal; and that on the coccygeal nerve, also in the canal, 

 is situated at some distance from the apparent origin of the posterior root. 



POSTERIOR 

 ROOTS 



ANTERIOR 

 ROOTS 



POSTERIOR 

 HOOTS ' 



LIGAMENTUM 

 DENTICULATUM 

 ANTERIOR 

 ROOTS 



SPINAL NERVE 

 IN ITS SHEATH 



FIG. 749 A portion of the spinal cord, showing its 

 right lateral surface. The dura is opened and arranged 

 to show the nerve roots. (Testut.) 



