416 



S. WALTER RANSON 



of the pyramidal with surrounding fibers as one sees in the human 

 cord. In the rat the tract stands out as sharply outlined in 

 the preparations as it is in the drawings. 



In the upper thoracic region the bundle changes its shape 

 somewhat, since the posterior surface forms an acute angle with 

 the medial surface; and the area occupied by the tract in sections 

 of this part of the cord has the shape of an eighth part of a circle. 

 Figure 5 was drawn from a Pal-Weigert preparation taken at 



Fig. 5 Fourth thoracic segment of the spinal cord. Ocu. 3, Obj. 3. 



about the level of the fourth thoracic segment and shows the 

 tract clearly outlined by its fainter staining from the remainder 

 of the white substance. 



In the mid thoracic segments the bundle becomes rounded or 

 oval in outline, and in the lower thoracic segments ( 7^.12) it 

 spreads out laterally along the posterior surface of the gray sub- 

 stance (fig. 6). In the upper lumbar region the outline of the 

 tract is no longer so sharply indicated, and the tendency to spread 



