TRACT OF LISSAUER 111 



ventro-laterally. In case the fibers on the lateral surface of the 

 columna posterior were derived from the dorsal root, one would 

 expect such ol^liciue fibers, since the dorsal root fibers would have 

 to run \'entro-laterally in order to reach a position lateral to the 

 cohunna posterior. The absence of such oblique fibers leads one 

 to suspect that this lateral extension of the tract is of endoge- 

 nous origin. If this assumption is correct, the non-medullated 

 fibers of the tract of Lissauer are in part of endogenous and in 

 part of exogenous origin. It is, of course, possible that the non- 

 medullated fibers in the lateral part have a long course and are 

 displaced ventro-laterally as they ascend, just as the fibers of the 

 fasciculus gracilis are displaced medially. This, however, is 

 highly improbable. 



In the seventh cer\'ical segment the fasciculus cuneatus con- 

 tains large and small medullated axons, the fasciculus gracilis 

 only medium-sized medullated axons; so that the two tracts are 

 clearly dift'erentiated in the sections (fig. 4). But both fascicles 

 are very poor in non-medullated fibers. This was also found to 

 be true in the cat, and indicates in a negative way that the non- 

 medullated fibers of the dorsal roots become separated from the 

 medullated at their entrance into the spinal cord and pursue a 

 different course within it. The light stain of the cerebellospinal 

 fasciculus is due to the fact that it is composed almost exclusively 

 of large medullated fibers. 



It is possible to trace both fine medullated and non-medullated 

 fibers from the cervical dorsal root into Lissauer's tract. But the 

 number of medullated fibers taking this course is relatively small 

 (fig. 7, l.p.p.r.). In pyridine-silver preparations bundles con- 

 taining very large numbers of non-medullated fibers can be seen 

 leaving the peripheral part of an entering radicle and running 

 into the tract of Lissauer. These have been traced in great 

 detail in the paper on '^ Lissauer's tract in the cat," and numerous 

 illustrations given. Here we will content ourselves with one 

 illustration. The entering rootlet shown in figure 10 is sur- 

 rounded by a constricting ring of pia, through the upper part of 

 which near the upper surface of the rootlet the section was taken. 

 This constricting band is seen at two points in the drawing 



