272 S. WALTER RANSON 



the case of the first sacral segment the non-medullated fibers sepa- 

 rate out along the septa separating the fascicles of the rootlet, 

 and run forward along these septa into the underlying Lissauer's 

 tract before the rest of the bundle has entered the cord. 



The non-medullated fibers of the dorsal root, then, enter the 

 tract of Lissauer, of which they form the chief and characteristic 

 part. They run for short distances in this tract chiefly in an 

 ascending direction and then probably pass forward into the 

 substantia gelatinosa. The close relation of Lissauer's tract to 

 this peculiar substance which caps the posterior horn, the fact 

 that fibers can be seen passing from one into the other, and 

 the fact that there is no other apparent outlet for the fibers oi 

 Lissauer's tract indicate that the substantia gelatinosa is the 

 probable nucleus of reception of these non-medullated fibers. The 

 fact that the substantia gelatinosa contains a large number of 

 very small nerve cells and many non-medullated nerve fibers is of 

 interest in connection with the probable relation of the two 

 structures. Experimental evidence is needed, however, to prove 

 this relation conclusively. 



So far as the function of the non-medullated fibers is concerned, 

 their course within the cord shows that they can have little or 

 nothing to do with the afferent impulses received from muscles 

 and joints which travel up the jjosterior funiculus. This does 

 not necessarily include muscle and joint pain. Their early ter- 

 mination within the gray substance would agree with the course 

 of the sensations of pain and temperature and probably also with 

 that of touch. But there are, of course, no data on which one 

 would care to hazard a guess as to their function, beyond the 

 statement that they can have little or nothing to do with those 

 sensations which are known to travel directly upward in the 

 posterior funiculus. 



