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THE NERVOUS SYSTEM 



commissure approximately on a level with the cells; others have 

 decussated in the medulla, and come down in the crossed pyram- 

 idal tract on the same side as the cells. In both cases the fibers 

 originated in the brain on the side opposite the cells around which 



FIG. 77. Course of nerve fibers in spinal cord. (Kirkes after Schafer.} 



they arborize in the cord. This is the connection which exists 

 between the brain and the anterior root fibers. 



Not all fibers in the anterior nerve roots are thus prolonged 

 upward in the pyramidal tracts. The number of fibers in these 

 roots is much larger than in the pyramidal tracts, and conse- 

 quently some of them must end (originate) directly in the cells 

 of the anterior cornua. Furthermore, it seems that some fibers 



