io6 



THE NERVOUS SYSTEM 



of the fiber tracts. In case of a complete transection of the spinal cord all the 

 ascending fibers whose cells are located below the cut will degenerate in the 

 segments above; while those descending fibers whose cells of origin are located 

 above will degenerate below the lesion (Fig. 75). Injury to the dorsal roots 

 proximal to the spinal ganglia causes a degeneration of the dorsal root fibers 



Dorsal spinocerebellar tract 

 f .fCorticospinal tract 

 i 



"Ascending branches of dorsal root fibers 



Fasciculus proprius 



Descending branch of dorsal root fiber 



Fig. 75. Diagram of the spinal cord to illustrate the principle of Wallerian degeneration. 

 The broken lines represent the degeneration resulting from 1, section of the ventral root; 2, 

 section of the spinal nerve distal to the spinal ganglion; 3, section of the dorsal root proximal to 

 the spinal ganglion, and 4, a lesion in the lateral funiculus. 



throughout their length in the spinal cord. Brain injuries may, according to 

 their location, result in the degeneration of one or more of the tracts which 

 descend into the spinal cord from above. 



By the study of a great many cases of injury to the central nervous system 

 in man and of experimentally produced lesions in animals a very considerable 



