lissauer's tract in the cat 269 



medially as one after another enters the cord. Figure 5 is a 

 diagrammatic representation of the level from which figures 6 and 

 7 were taken. At a is indicated the tract of Lissauer; b and c 

 represent connective tissue septa. In the high power drawings 

 the same lettering has been used. In figure 6 one sees that most 

 of the non-medullated fibers have separated out from among the 

 medullated and arranged themselves along the septa b and c. 

 At d and d' are seen bundles of non-medullated fibers arranged 

 along the inner border and the medial part of the posterior border 

 of the radicle. The fibers in bundle d can be traced at this level 

 into Lissauer's tract. The fibers in d' can be traced along the 

 surface of the cord for a short distance and then turn ventrally 

 into the same tract. Bundle c is composed of fibers which have 

 separated out from the two root fascicles between which it lies. 

 It is composed of two layers of fibers arranged one on each side 

 of a connective tissue septum. If one follow this bundle upward 

 in the serial sections its fibers are seen to turn ventrally and run 

 into the tract of Lissauer (fig. 7, c). These fibers along the con- 

 nective tissue septa of the roots are in size and staining reaction 

 exactly like the non-medullated fibers which farther distally are 

 scattered uniformly through the roots. They are also identical 

 in size and staining reaction with the non-medullated fibers of 

 the tract of Lissauer into which they have just been followed. 

 It seems that a clearer demonstration of the fate of the non- 

 medullated fibers of the dorsal roots could scarcely be desired. 



In the fifth lumbar segment of the cat's cord the entering 

 radicles are smaller. Only when they are covered by a thick 

 coat of connective tissue and bound down tightly to the surface 

 of the cord are the physical conditions satisfactory for the impreg- 

 nation of the non-medullated fibers. Figures 4 and 8 show such 

 a rootlet entering the cord. Notice that its fibers pass through 

 Lissauer's tract and separate off a small dorso-median portion 

 from the main tract. This unites again with the rest of the 

 tract above and below the entering root bundle. The constrict- 

 ing ring at the entrance of a radicle into the cord is well seen in 

 figure 8. Points a and c are joined in the thickness of this sec- 

 tion and the next by an arched band of connective tissue. The 



