140 SUTHERLAND SIMPSON 



the margin of the ventral longitudinal fissure (direct ventral 

 tract). Some fibers are also found in the dorsal column of the 

 same side, forming a direct dorsal tract. 



In the brief summary of previous work on the subject given 

 above, no mention has been made of the methods employed, but 

 in the great majority of cases these were faulty, consisting as they 

 did in the examination of serial sections from normal histologi- 

 cal preparations. Particularly has this procedure been adopted in 

 the case of the smaller rodents and insectivors, where the dif- 

 ficulty of operating on the living animal is considerable. 



In this relation it should be kept clearly in mind that only 

 two methods are available for tracing the paths of fiber bundles 

 in the central nervous system, namely, the embryological method 

 of Flechsig and the Wallerian method of secondary degeneration. 

 The latter, when followed by Marchi staining, is always to be 

 preferred. As Edinger truly says ''Ein echter Tractus cortico- 

 spinalis ist nur durch Degenerations versuche zu erkennen. Diese 

 fehlen noch fiir allermeisten Sanger." 



Granted that in serial sections through the decussation in 

 normal preparations the fibers can be traced into one or other 

 of the columns of the spinal cord, it is begging the question to 

 say that these same fibers have their origin in the cerebral motor 

 cortex. They may have some other source and may have joined 

 the tract at a lower level, in which case they will not belong to the 

 pyramidal system and will certainly not be cortico-spinal fibers. 

 Again, where tke degeneration method is not used, it is impos- 

 sible to say whether the decussation is partial or complete. Take 

 as an example the case of the cat, dog, or monkey, where there is a 

 crossed lateral and also a direct lateral tract in the cord. When 

 the cortical lesion is unilateral only one pyramidal system under- 

 goes degeneration and at the decussation, if the Marchi method 

 has been used, it is plainly seen that while most of the fibers decus- 

 sate into the opposite lateral column, some pass into the corre- 

 sponding column of the same side without crossing the raphe. 

 If both pyramids were degenerated, or if the fibers were traced 

 in normal preparations, the presence of. this direct tract would 



