110 S. WALTER RANSON 



oblique fiber passing from this lateral part into the dorsal part 

 of the tract. Leszlenyi has made much of this spreading out of 

 the tract of Lissauer into the lateral funiculus. He saw in a 

 great variety of animals fibers running into Lissauer's tract pro- 

 per from this extension in the ground bundle of the lateral fu- 

 niculus, and concluded that many of the fibers of the tract were 

 derived in this way from the ground bundle. Leszlenyi was 

 working with Pal-Weigert preparations and was impressed with 

 the similar light staining and open structure of the two regions, 

 and he was led in this way to attempt to show a connection be- 

 tween the two. The similarity in Pal-Weigert preparations is, 

 however, not nearly so striking as in pyridine-silver preparations 

 where both are seen to be crowded with fine axons. Although I 

 can find no evidence in support of Leszlenyi's derivation of the 

 dorsal part of the tract out of oblique fibers from the lateral, I 

 do not doubt that the two regions are intimately associated, 

 and are best described together under the head of Lissauer's 

 tract. 



In pyridine-silver preparations, the tract of Lissauer is closely 

 packed with many very small and a few medium-sized axons 

 (figs. 4 and 9). The very small axons are non-medullated. If 

 one compares a pyridine-silver preparation (fig. 9) with a Pal- 

 Weigert preparation (fig. 8), one sees that the number of axons 

 is far in excess of the number of myelin sheaths, but that the 

 latter are about as numerous as the medium-sized axons. These 

 closely-packed, darkly-stained axons give the tract its charac- 

 teristic dark appearance in pyridine-silver preparations. As in 

 Pal-Weigert preparations, most of the fillers are vertical; but 

 there are some that are horizontal and oblique. In the extension 

 of the tract in the lateral funiculus the fine, non-medullated 

 axons are also very numerous. As has been mentioned, a few 

 large medullated fibers are found scattered through this lateral 

 area; and these give this region a lighter appearance than the 

 dorsal part, although between these large fibers the fine axons are 

 as closely packed as in the dorsal portion of the tract. 



There are fewer oblique or horizontal fibers in the lateral than 

 in the dorsal part of the tract, and practically none riuining 



