A NOTE ON THE DEGENERATION OF THE FASCICULUS 

 CEREBRO-SPINALIS IN THE ALBINO RAT 



S. WALTER RAXSOX 



From the Aiuilomlcal Luboratory of the Northwestern Unieersity Medieal School 



ONE FIGURE 



The oerpbro-spinal or pyramidal tracts of the rat decussate 

 in the medulla and run through the spinal cord in the ventral 

 part of the posterior funiculi (Spitzka '86, Von Lenhossek '89, 

 Bechterew '90, Goldstein '04, Van der Vlort '06 and King '10). 

 More recently it has been shown that the pyramidal tract is 

 not well medullated in the adult rat and that it consists of fine 

 and medium-sized medullated fibers and great numbers of non- 

 medullated axons (Ranson '13). Because of its incomplete 

 medullation it stains a light grayish blue in Pal-Weigert j^rep- 

 arations, while in pyridine-silver preparations the closely packed 

 darkly stained axons give the tract a dark bro\Mi color which 

 clearly differentiates it from the remainder of the substantia alba. 



The degeneration of this tract after destruction of the motor 

 cortex has been studied in the rat with the Marchi stain by Gold- 

 stein, Van der Vlort and King. These studies have shown that 

 the medullated fibers in this tract are of cortical origin. In 

 my previous paper I assumed that the non-medullated fibers 

 of the tract have the same origin, namely, from cells of the motor 

 cortex. No evidence was presented to show that the motor 

 cortex was actually the source of these fibers, and there remained 

 open the possibility that the non-medullated fibers in the pyrami- 

 dal tract were not pyramidal fibers at all but a separate tract 

 arising from lower centers of the brain, joining the pyramidal 

 tract, decussating with it and accompanying it along its course 

 through the cord. While this possibility is indeed remote, it 

 seems worth while to present definite proof of the cortical origin 

 of the non-medullated fibers of the pyramidal tract. 



503 



