364 THE SPINAL CORD. 



etc., hence the twitchings, spasms and convulsions. Their de- 

 struction causes flaccid paralysis (lower segment paralysis). In 

 spinal meningitis both the anterior and posterior roots are affected. 



The posterior root (radix posterior] is the sensory, or afferent 

 root (Figs. 100 and 104). It is larger than the anterior root, 

 except in the case of the first cervical nerve; and is composed of 

 from six to eight fasciculi, which also combine at once into two 

 bundles. The posterior root pierces the dura mater separately 

 from the anterior root. It unites with the anterior root in the 

 intervertebral foramen. Near the outer end, it presents a swell- 

 ing which contains large vesicular unipolar cell-bodies and is called 

 a spinal ganglion (ganglion s pinole). The ganglion (Figs. 100 

 and 128) and posterior root are occasionally absent on the first 

 nerve. The posterior root, external to the ganglion, is made up 

 of the dendritic processes (Cajal) of the ganglion cells. These 

 dendrites, which in appearance are axones, extend to the most 

 distant parts of the body; they are the sensory fibers of the spinal 

 nerves. On the proximal side of the ganglion, the posterior root 

 is composed of axones, which rise from the ganglion cells. Both 

 the axonic and dendritic processes are medullated. 



Apparent Central Termination (Fig. 104). The posterior roots 

 of the spinal nerves enter the posterior-lateral sulcus; and, at 

 once, divide into an outer set of small fibers and an inner set of 

 large fibers with some small ones interspersed. The fibers of each 

 set bifurcate into a large ascending and a smaller descending 

 branch. Collaterals rise from the parent axone and from both 

 branches. 



Real Central Termination, Terminal Nuclei (Fig. 104). The 

 ascending divisions of the outer set of fibers run a short distance 

 along the external surface of the posterior columna, and end in 

 ramifications about the cell-bodies of the substantia gelatinosa. 

 They form the marginal tract (of Lissauer). Probably their de- 

 scending branches have the same ending. The T-branches and 

 collaterals of the inner set of fibers from the posterior root run : 

 (i) To the gray matter of the cord, viz. : To all parts of the 

 posterior columna, to the center of the crescent, and to the anterior 

 columna on the same side, and, through the posterior commis- 



