LISSAUER^S TRACT IN THE CAT 261 



darker brown according to the number of dark brown non-medul- 

 lated axons which they contain. Under higher magnification the 

 non-medullated axons are sharply differentiated from the faintly 

 yellow, granular neuroglia. The neuroglia fibers are not differ- 

 entiated. 



We wish briefly to call attention to those tracts which imme- 

 diately surround the posterior cornu. 



The cuneate and gracile fasciculi are composed very largely of 

 medullated fibers (fig. 1). But in the neighborhood of the pos- 

 terior commissure and posterior cornu there are numerous non- 

 medullated fibers probably of endogenous origin. On the whole, 

 however, these two fasciculi contain fewer non-medullated fibers 

 than any other portion of the substantia alba, with one exception 

 to be mentioned later. They are for this reason more lightly 

 stained than is the anterior and most of the lateral funiculus. 

 The number of non-medullated fibers in the fasciculus cuneatus 

 and fasciculus gracilis is not sufficient to account for an upward 

 continuation in these columns of the non-medullated fibers of the 

 dorsal roots, and indicates that one must look elsewhere for their 

 course within the cord. 



The dorsal spino-cerebellar tract is also composed chiefly of 

 medullated fibers, and is the most lightly stained of all the fiber 

 columns of the cord. It is indicated in figure 1, c, as a light area 

 contrasting sharply with the darker pyramidal tract (d) and the 

 still darker tract of Lissauer (6) . It is broadest near its posterior 

 medial extremity where it is sharply marked off from the latter 

 tract by a rather thick pial septum. It becomes gradually less 

 distinct in an antero-lateral direction. Ventro-medially from 

 this fasciculus and separated from it by no very sharp line is the 

 pyramidal tract, d. The area occupied by the latter is somewhat 

 rounded in outline and lies just lateral to the cervix and caput 

 of the posterior cornu. ' Sharply outlined by its dark staining 

 from the dorsal spino-cerebellar fasciculus, it is not so clearly 

 separated from the remainder of the lateral funiculus. Next to 

 Lissauer's tract the pyramidal tract is the darkest part of the 

 substantia alba, and contains a very large number of non-medul- 

 lated fibers. In comparison with the tract in the rat (Ranson '13), 



