c.a 



Fig. 4 From the seventh cervical segment of the spinal cord of the cat. Pyri- 

 dine-silver. X 40. Of all the tracts the cerebello-spinal fasciculus stains the 

 lightest. It is composed almost exclusively of large medullated fibers whose 

 axons are light yellow and whose myelin sheaths are colorless. The fasciculus 

 cuneatus, which is composed of large and medium sized medidlated fibers with 

 very few non-medullated axons, stains somewhat darker than the preceding tract. 

 The pyramidal tract, containing small and medium sized medullated fibers and 

 many non-medullated axons, stains still more darkly. Its outline is sharply 

 indicated posteriorly where it borders upon the cerebello-spinal fasciculus. 

 Ventrally and laterally its outline is less distinct. The tract of Lissauer stains 

 much darker than any of the others and is composed of scattered fine medullated 

 fibers and great numbers of non-medullated axons. These differences in the 

 structure of the various fasciculi of the cord have been discussed in detail by 

 Ranson ('13, '14). 



521 



