PYRAMID TRACT IN SQUIRREL AND CHIPMUNK 



151 



Transverse section through fourth cervical segment {Jig. 14)- The 

 tract now occupies the apex of the posterior column being squeezed 

 in between the median septum and the base of the posterior horn. 

 The outline is still triangular but the base at this level is directed 

 backward and the apex forward while the mesial border is con- 

 siderably shortened. 



Fig. 

 Fig. 



Fig. 17 

 Fig. 18 

 Fig. 19 



Transverse section, seventh cervical segment. X 12. 

 Transverse section, second thoracic segment. X 12. 

 Transverse section, eighth thoracic segment. X 12. 

 Transverse section, second lumbar segment. X 12. 

 Transverse section, fifth lumbar segment. X 12. 



Transverse section through seventh cervical segment {fig. 15). 

 At this level there is little change; the tract is somewhat reduced 

 in size and the degenerated fibers are less numerous. 



Transverse section through second thoracic segment {fig. 16.) The 

 outline of the tract here resembles that seen in the second cer- 

 vical segment, being triangular in form with the base lying against 

 the posterior commissure and the apex pointing backward. Be- 

 tween this and the seventh cervical segment a large number of 

 fibers have disappeared. 



