lissauer's tract in the cat 267 



I 



in size from lower to high levels in the cord. But the tract seems 

 rather to be proportional in size to the entering rootlets; and 

 instead of a steady increase in size in an ascending direction, there 

 is a marked decrease in going from the lower lumbar into the 

 thoracic cord and again in passing from the lower cervical to the 

 upper cervical segments. These facts indicate that the majority 

 of the non-medullated fibers are short ascending fibers and in the 

 next section we will show that many, probably a great majorit}^, 

 are derived from the dorsal roots. 



Entrance of the dorsal roots into the spinal cord 



Pal-Weigert preparations. In 1885 Lissauer observed that fine 

 medullated fibers grouped themselves on the lateral side of an 

 entering rootlet and turning lateralward separated themselves 

 from the remainder of t^he rootlet to enter the apex of the pos- 

 terior horn, where they turned to run vertically in the tract which 

 now bears his name. Similar observations were made by Bech- 

 terew ('86), and have formed the basis of the standard text-book 

 accounts of this tract. It is an easy matter to confirm these 

 observations in Pal-Weigert preparations of the cat's cord, espe- 

 cially in the case of the larger cervical and sacral roots. There 

 can be no doubt that in the cat medullated fibers enter the tract 

 of Lissauer from the dorsal roots in considerable number, and in 

 exactly the manner described by Lissauer and Bechterew. Therd 

 can also be no doubt, on the basis of the pathological and experi- 

 mental evidence presented in preceding paragraphs, that these 

 mxedullated fibers from the dorsal root do not constitute all or 

 even the majority of the medullated fibers in this tract. 



Pyridine-silver preparations. To the medial side of the tract of 

 Lissauer is the entering root zone. In this region the medullated 

 fibers, which have just entered the cord, can be seen running 

 more or less obliquely (fig. 10, a). The fibers seen here are for 

 the most part large medullated ones; and, when one remembers 

 the large number of non-medullated fibers seen in the dorsal root, 

 one is impressed with the scarcity of these fibers in the entering 

 root zone. Somewhat further medialward large numbers of fine 



