TRACT OF LISSAUER 119 



ward through the thin part of the layer on either side of the 

 substantia gelatinosa. There are also a very large number of 

 vertical fibers. It would seem from its position and structure 

 as if the stratum zonale served as a means for the passage of the 

 fibers of the tract of Lissauer to and from the substantia gela- 

 tinosa. In Pal-Weigert preparations (fig. 7, S.Z.) this layer con- 

 tains but very few fibers, most of which are horizontal and very 

 few vertical in their course. It is easy to see that these are 

 chiefly derived from the vertical and horizontal medullated fibers 

 of Lissauer's tract, and the impression is also gained in Pal- 

 Weigert preparations that this layer serves as a means of inter- 

 change of fibers between the tract of Lissauer and the substantia 

 gelatinosa. 



The second laj-er or substantia gelatinosa proper is somewhat 

 lighter in pyridine-silver preparations and contains a consider- 

 able amount of light-yellow intermediate substance, which, as 

 has been shown, the most recent authorities regard as an arti- 

 fact due to the destruction of protoplasmic elements. The pic- 

 ture which this technique gives of this region is therefore not to 

 be regarded as a complete one. This second layer contains, 

 however, a great number of very fine axons running in every 

 direction and forming a loose network. While the number of 

 fibers is large, it is much less than in either the layer just dorsal 

 or the layer just ventral to it, and for this reason it was repre- 

 sented rather light in the drawing to secure the proper contrast. 

 The number of medullated fibers in this region is very small. 



We should perhaps distinguish a third layer in the substantia 

 gelatinosa, or better describe a layer of fibers just ventral to it 

 and between it and the nucleus of the columna posterior. Here 

 the fiber plexus is especially dense and there is as an added 

 element a very large number of vertical fibers. In Pal-Weigert 

 preparations only a relatively few medullated fibers are seen, 

 and these are chiefly horizontal, running from the second layer 

 of the substantia gelatinosa toward the nucleus of the columna 

 posterior. ]Most of the fibers and especially of the vertical 

 fibers in this region 'are non-medullated. Rosenzweig has called 

 attention to this layer as a longitudinal conduction path com- 



