152 SUTHERLAND SIMPSON 



Transverse section through eighth thoracic seginent {jig. 17). At 

 this level the tract is greatly reduced in size; it occupies a com- 

 paratively small area at the apex of the column. 



Transverse section through second lumbar segment {fig. 18). The 

 degenerated fibers are now found in close relation to the base 

 of the posterior horn; they have left the middle line and extend 

 along the mesial border of the gray matter, but no fibers have 

 been observed entering the gray matter at this or any other level 

 in the spinal cord. 



Transverse sectioii through fifth lumbar segment {fig. 19). All 

 that represents the crossed pyramid tract here are a few scattered 

 fibers lying close to the gray matter. In this particular animal 

 the degeneration cannot be followed farther than this segment, 

 but in one of the three squirrels used in these experiments some 

 fibers are still present in the last sacral segment. 



For the squirrel these results agree with those of Goldstein ('03) 

 who found that the decussation in the lower part of the medulla 

 oblongata is complete, all the fibers passing into the posterior 

 columns. With regard to the course of the tract in the spinal 

 cord he gives no details. He was chiefly concerned with the be- 

 havior of the fibers at the decussation. For this animal he 

 was the first to use the degeneration method and so to prove 

 that there does exist a cortico-spinal tract. 



Fig. 20 Brain of chipmunk, dorsal view, showing position of lesion in left 

 cerebral hemisphere. Magnified \. 



