AN EXPERIMENTAL STUDY OF LISSAUER'S TRACT 

 AND THE DORSAL ROOTS 



S. WALTER RANSON 

 From the Anatomical Laboratory of the Northwestern University Medical School 



FIVE FIGURES 



As a dorsal root enters the cord it divides into two parts. The 

 larger medial portion consists of medullated fibers and enters 

 the cuneate fasciculus; the smaller lateral portion consists of a 

 few fine medullated fibers with great numbers of non-medullated 

 fibers and enters Lissauer's tract. These and the following 

 introductory statements are made on the basis of our studies on 

 the tract of Lissauer, published in 1913 and 1914. In these 

 papers the related literature has been fully considered. 



The tract of Lissauer is composed of small, somewhat widely 

 separated, medullated fibers, and a great number of fine non- 

 medullated axons. The number of medullated fibers entering 

 the tract from the dorsal root is not sufficient to account for all 

 the medullated fibers found there. For this and other reasons 

 it seemed certain that the majority of the medullated fibers in 

 the tract were not derived from the dorsal root but were endoge- 

 nous. Since a much greater number of non-medullated fibers 

 enter the tract from the dorsal root, it seemed fair to assume that 

 a majority of these fibers in the tract came from this source. It 

 was shown, however, that some of these non-medullated fibers 

 were of endogenous origin, at least in certain animals. In the 

 rhesus monkey, for instance, the tract spreads out into the lateral 

 funiculus along the side of the columna posterior. Since no ob- 

 lique fibers were found running from the dorsal roots towards 

 this lateral expansion of the tract, the fibers, both medullated 

 and non-medullated, which were found in this part of the tract, 

 were considered to be of endogenous origin. It seemed probable 



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