THE NERVOUS SYSTEM 



of the root and enter the dorsolateral fasciculus or tract of Lissauer (Fig. 72).' 

 The medial division, on the other hand, consists exclusively or almost exclu- 

 sively of myelinated fibers. The fibers of the lateral division of the root divide 

 into ascending and descending branches, both of which, however, are very 

 short. The ascending branch, which is the longer of the two, does not extend 

 at most more than the length of one or two segments in the long axis of the 

 cord (Ranson, 1913, 1914). 



The dorsolateral fasciculus, or tract of Lissauer, lies between the apex of 

 the posterior column and the periphery of the cord, and varies greatly in shape 

 and size in the different levels of the cord (Figs. 55-58). It is composed of 



Medial division of dorsal root 



~^X. Fasciculus cuneatus 



Dorsolateral 

 fasciculus 



Lateral division of dorsal 

 root 



_ Dorsal spino- 

 cerebellar tract 



Dorsal spinocerebellar tract 



\< (' ^S=fe- ^^ J 



__. Ventral spino- 

 cerebellar tract 

 Lateral spino- 

 thalamic and 

 spinotectal tracts 

 Ventral spinothalamic 

 tract 



Fig. 72. Diagram of the spinal cord and dorsal root, showing the divisions of the dorsal root, 

 the collaterals of the dorsal root fibers, and some of the connections which are established by 

 them. 



unmyelinated and fine myelinated fibers, which are derived in part from the 

 lateral division of the dorsal root and in part arise from cells in the neighboring 

 gray matter (Fig. 63). 



AFFERENT PATHS IN THE SPINAL CORD 



We have been at some pains to make clear the course and distribution of 

 the dorsal root fibers within the spinal cord because all afferent impulses which 

 reach the cord are carried by them. Interoceptive fibers from the viscera, 

 proprioceptive fibers from the muscles, tendons, and joints, as well as extero- 

 ceptive fibers from the skin are included in these roots; and among the latter 

 group are probably several subvarieties, mediating the afferent impulses out 



