TRACT OF LISSAUER 103 



upon the lateral surface of the columna posterior as in the mon- 

 key. It is characteristic of the tract in the thoracic portion of 

 the human cord that it is broken up by the entering rootlets, 

 which run through it toward the gray substance. 



In the third lumbar segment (fig. 3) the substantia gelatinosa 

 reaches much nearer to the surface than in the two levels just 

 described, and the tract of Lissauer is compressed between it 

 and the surface of the cord. Instead of being long and slender, 

 the tract at this level is short and broad. It is not sharply 

 defined on either side, but spreads out near the surface of the 

 cord into the lateral funiculus and even to a greater degree into 

 the i>osterior funiculus. It does not extend forward upon the 

 lateral surface of the columna posterior. The fila radicularia 

 pass through it, breaking it up into two or more divisions. 



Structure 



In Pal-Weigert preparations the tract is clearly outlined from 

 the other filler columns by its light color. It contains fine and 

 medium-sized meduUated hbers rather sparsely arranged. These 

 are for the most part vertical (in line with the long axis of the 

 cord), but there are also horizontal and oblique fibers. In my 

 preparations I was unable to see medullated fibers from the dor- 

 sal roots entering and becoming a part of the tract of Lissauer, 

 Large bundles of medullated fibers run through the tract on 

 their way to the fasciculus cuneatus and the columna posterior;, 

 but it is difficult to demonstrate indi\ddual fibers leaving these 

 bundles to become a part of the tract. A good set of serial Pal- 

 Weigert sections would probably show a few such fibers. Lesz- 

 Icnyi believes that such dorsal root fibers as do enter the tract 

 are horizontal and run directly into the substantia gelatinosa. 



In pyridine-silver preparations the tract of Lissauer is stained 

 much darker than any other part of the fiber columns of the 

 cord and is seen to be composed of closely packed, fine axons, 

 the majority of which are non-medullated. In the thoracic 

 cord, because of the intimate relation of the entering radicles 

 to the tract of Lissauer, it is more difficult to trace the non-med- 



