518 A. J. LINOWIECKI 



ameters. This reduced number accounts for the Ughter staining 

 quaUty of the tract, which however was prominent enough to 

 leave no doubt as to its topography. 



The Pal-Weigert sections at this same level show the area 

 occupied by the tract to be of light blue color while the rest of 

 the substance has a somewhat deeper color. The outline of the 

 tract is very indistinct. The myelin sheaths are larger than 

 those seen in the rat cord and their number is quite small as 

 compared with the number of axons seen in the pyridine-silver 

 preparation. 



On tracing the tracts caudalwards the pyridine-silver prep- 

 arations show the tracts to have about the same shape at the 

 level of the fourth thoracic segment. At the level of the eighth 

 thoracic segment the tracts assume a crescent shape, and a very 

 diffuse, indistinct and very markedly decrease in size. There 

 is an evident decrease in the number of axons. When the level 

 of the twelfth thoracic segment is reached, the tracts, though 

 quite distinct, are smaller and consist of two compact groups of 

 axons which have become separated at the posterior median 

 septum. Some groups of axons are seen scattered throughout 

 the posterior funiculus. Proceeding caudalwards the tracts 

 become less distinct and at the level of the second lumbar seg- 

 ment the groups tend to move posteriorly and separate from each 

 other. They have no definite outline and stain very lightly. 

 From here on, the tracts narrow markedly and fade in color and 

 at the level of the fifth lumbar segment they consist of two narrow 

 strips on each side of the posterior median septum. They take 

 a very light stain, the fibers are markedly reduced in number 

 and the tract is barely visible. 



V. Lenhossek ('89) and Bechterew ('90) located the tract in 

 the posterior columns and mention the fact that it is not a com- 

 pact mass as in the rat, though it is more developed than in the 

 mouse, v. Lenhossek also expresses the area occupied by the tract 

 at the level of the middle cervical segment, as being 3 per cent 

 of the total transverse area of the cord. Rebeley and Simpson 

 ('09), who also located the tract in this region, state that the 

 fibers diminish rapidly in number as they travel caudalwards. 



