524 A. J. LINOWIECKI 



III th(^ pyridine-silver preparations the tract is seen to he 

 prominently set off from the rest of the white substance (fig. 6). 

 It is stained deep brown. The axons are densely packed in the 

 field and very small. It is due to their great numbers as com- 

 pared with the myelin sheaths, that the tract stains so heavily 



c c 



.c a 



-p.t. 



im.a. 



Fig. 6 From a section taken at about the first cervical segment of the spinal 

 cord of the mole (Scalopus aquaticus). Pyridine-silver. X 93. The pyramidal 

 tract is larger than in figure 5, is deeply stained, and sharply outlined from the 

 rest of the ventral funiculus. This deep staining is due to the closely packed 

 fine non-medullated fibers of which it is composed. 



and stands out so clearly from the rest of the white substance 

 which has a very light brown color. In tracing the tract caudal- 

 wards through a set of serial sections of the entire cervical cord, 

 it was found that the anterior median fissure bisected this oval 

 field only at certain levels; while at others, some axons extend 

 across the fissure thus connecting the two tracts by a bridge of 

 decussating fibers. Such a bridge across the anterior median 

 fissure would extend through about 13 consecutive sections of llju 

 thickness. In different sections the same bridge of fibers would 

 occupy a different antero-posterior level. At times it w^ould 



