90 PEARL BRIGGS BULLARD 



to Hai'desty ('02), has a part at least of the pyramidal tract 

 situated on either side of the mid-line between the dorsal and 

 ventral lamina of the grey commissure. Believing that it corre- 

 sponds to the lateral or crossed pyramidal tract in man, he has 

 designated it 'fasciculus cerebro-spinalis internus' (fig. 1, C and 

 Th). Burkholder ('04) describes this tract in the sheep as oc- 

 cupying the same position as in the elephant and has termed it 

 the 'fasciculus cerebro-spinalis internus' after Hardesty. King 

 and Simpson ('10) state that the pyramidal fibers for the sheep 

 are situated in the reticular formation in the lateral aspect of the 

 dorsal horn. The specimen of sheep here studied, as well as 

 the ox, presents in all three regions a structure identical in posi- 

 tion to that described by Burkholder (figs. 3 and 7, C, Th and L). 

 Symington ('08) states that the kangaroo has the pyramidal tract 

 in the dorsal funiculus and the rabbit has the tract in the lateral 

 funiculus. 



I have compared sections through the pyramidal decussation 

 in the medulla of the agouti and opossum with those of the rat, 

 mouse and kangaroo, and am of the opinion that the pyramidal 

 tract in the former animals, as well as in the latter, is situated 

 in the dorsal funiculus. The agouti, like the rat, mouse and 

 guinea-pig, is a rodent, while the opossum, being a marsupial, 

 is related to the kangaroo. From an examination of sections 

 through the medulla of the raccoon and of the fox, the pyramidal 

 fibers appear to course in the reticular formation. However, the 

 experimental method is the only trustworthy one for determining 

 the position of any fiber tract. 



Comparison of funiculi. As is to be expected, all of the 

 cords here considered have, in each region, a dorsal funiculus 

 which is exceeded in actual area in transverse section by the 

 ventro-lateral funiculus (table 6). The comparative size of the 

 funiculi can be best expressed in the form of a ratio. Table 8 

 {a and b) record such ratios for each region, obtained by divid- 

 ing the area of the ventro-lateral funiculus by that of the dorsal 

 funiculus. It is clear that the higher the ratio, the smaller 

 relatively is the dorsal funiculus. For example, table 8a, col- 

 umn 4, gives man as having the lowest average ratio, 2.10, which 



