262 S. WALTER RANSON 



the cat's pyramidal tract is much better medullated and contains 

 in addition to non-medullated and small medullated axons also 

 large axons with thick myelin sheaths. This is not the place, 

 however, to enter into a discussion of the comparative histology 

 of the pyramidal tract. 



Lissauer's tract 



Pal-Weigert preparations. Lissauer's tract occupies the apex of 

 the posterior cornu, lying just dorsal to the substantia gelatinosa. 

 It occupies the entire apex, reaching to the surface of the cord, 

 except in the thoracic segments. Here the substantia gelatinosa, 

 capped by the tract of Lissauer is at some distance from the sur- 

 face; and the posterior part of the apex consists of a thin pial 

 septum. Because of the light stain which the tract takes in 

 Weigert preparations it is usually considered as a part of the 

 posterior cornu, although it is admitted by all that it properly 

 belongs with the longitudinal fiber columns of the cord. 



In Pal-Weigert preparations it is seen to consist of rather 

 sparsely arranged and uniformly fine medullated fibers. The 

 spacing is uniform, each fiber being separated from its neighbors 

 by a considerable interval. There is no grouping of these fibers 

 into bundles nor are there any large spaces devoid of fibers. The 

 fibers for the most part run vertically in the bundle, but some 

 have an inclination forward toward the substantia gelatinosa. 

 The obliquity of the fibers is most pronounced at the posterior 

 extremity of the tract and in the neighborhood of entering root 

 bundles. Starting in the region of an entering root bundle and 

 passing forward toward the substantia gelatinosa, one can often 

 see all gradations between horizontal fibers, and oblique fibers 

 and again between oblique and vertical fibers. This would be in 

 harmony with the generally accepted view that the medullated 

 fibers of this tract are derived from the dorsal root, a view which 

 has recently been called into question. In addition to the verti- 

 cal and oblique fibers, just mentioned, one sees horizontal fibers 

 of fine caliber, a few in each section running long distances through 

 the tract to enter the stubstantia gelatinosa. These are prob- 



