THE SPINAL CORD AND ITS NERVES 



129 



in Fig. 58. Figure 59 illustrates diagrammatically the ar- 

 rangement of the chief fiber tracts in the same region. 



The spinal cord has two main groups of functions, first, as a 

 system of reflex centers for all of the activities of the trunk and 

 limbs; second, as a path of conduction between these centers 

 and the higher correlation centers of the brain. The former 

 group is the more primitive, and there is evidence that in the 



Dorsal median septum 



Septum 

 Dorsal lateral groove 



Dorsal nerve root 

 Substantia gelatinosa 



Root-fibers entering gray 



matter 

 Processus reticularia 



Central canal 



Nucleus from which \ 



motor fibers for 



muscles of upper 



limb arise 



Ventral white commis- 

 sure 



Ventral nerve root 



Ventral median fissure 



Fig. 58. Cross-section through the human spinal cord at the level of 

 the fifth cervical nerve, stained by the method of Weigert-Pal, which colors 

 the white matter dark and leaves the gray matter uncolored. (From 

 Cunningham's Anatomy.) 



course of vertebrate evolution the higher centers, especially the 

 cerebral hemispheres, exert an increasingly greater functional 

 control over these reflex centers (see p. 280). The long conduc- 

 tion paths between the spinal cord and the cerebral hemispheres 

 are, accordingly, much larger in man than in lower vertebrates. 

 It is impossible in the space at our disposal to summarize even 

 the most important of the internal connections of the spinal 

 nerves; we can only select a few typical illustrative examples. 

 9 



