422 S. WALTER RANSON 



on the normal side, a decrease which could be accounted for by 

 the presence of a few dorsal root fibers within the area of the 

 tract. Since the tract decreased so little in size and since there 

 were no other evidences of degeneration within its territory, it 

 is obvious that the non-medullatd fibers which it contains do not 

 belong to another system arising in the do-rsal root ganglia. 

 These experiments also serve to emphasize the sharpness with 

 which the regions occupied by the pyramidal tracts are limited 

 in the white rat. 



Watson ('03) noticed that in the Pal-Weigert preparations of 

 the spinal cord of the adult albino rat the pyramidal fasciculus 

 was only slightly stained and he attributed this to a supposedly 

 different chemical composition of the myelin in the sheaths of 

 these fibers. Miss King ('10) states that, when compared with 

 the Marchi preparations of the pyramidal fasciculus in the rabbit, 

 cat and dog, the Marchi preparations of this tract in the rat 

 re\'eal a striking paucity of fibers ''so that in this animal the so- 

 called primary motor path is probably only of secondary impor- 

 tance." In view of the incomplete medullation of the pyramidal 

 tract in the rat it is easy to understand Miss King's results. 

 Although there is an abundance of axons there are few well med- 

 ullated fibers, such as would respond readily to the Marchi stain. 

 Just how far the incomplete medullation of this tract is an indi- 

 cation of an incomplete development of its function is a matter 

 which it would be very difficult to decide. Attention has been 

 called to the peculiar light staining of this fasciculus in Weigert 

 preparations of the spinal cord of animals belonging to widely 

 separated groups. Ziehen ('99 and '00) mentions it as occurring 

 in the pseudochirus, the sheep and the rat. Driiseke ('04) observed 

 that in the mole the pyramidal fibers lose their myelin sheaths as 

 they pass from the medulla into the anterior funiculus of the 

 spinal ct)rd, into which they go without decussation. Here they 

 form a medially placed oval field somewhat ventral to the ante- 

 rior commissure. This oval area is very faintly stained in Weigert 

 preparations and is almost devoid of medullated fibers. Bischoff 

 ('00) states that in the hedgehog the pyramidal fibers are so fine 

 and possess so delicate a myelin sheath that the Marchi stain 



