PRINCIPAL REGIONS OF SPINAL CORD 93 



the two fasciculi of which it is largely composed contain a large 

 proportion of spino-cerebral fibers ascending from all segments 

 of the cord and thus it must increase in size from below upward. 

 However, column 3, table 8a, shows the lumbar region of the 

 human cord to possess a larger relative size for the dorsal funicu- 

 lus than either of the other two regions. The pyramidal tract, 

 in the ventro-lateral funiculus, which has its maximum size in 

 the cervical region is one of the principal factors in reducing the 

 relative size of the dorsal funiculus in this region. Another fac- 

 tor in the lumbar enlargement is the large proportion of associa- 

 tion fibers in the dorsal fasciculi proprii of the dorsal funiculus. 



In those animals in which the crossed pyramidal tracts course 

 in the dorsal, instead of in the lateral funiculus, one would ex- 

 pect a relatively larger area of dorsal funiculus and a resultingly 

 smaller area in the ventro-lateral funiculus. Reference to these 

 animals in tables 8a and 8b does not show a relatively greater 

 area of the dorsal funiculus (smaller ratio of the ventro-lateral 

 funiculus) to be of distinguishingly constant occurrence. In 

 some cases, agouti, guinea-pig and rat, for example, the ratios for 

 the cervical region are approximately the same as those for the 

 lumbar region in spite of the fact that there are both ascending 

 and descending fibers in the dorsal funiculus which must in- 

 crease as the cord is ascended. 



In all mammals, there is a decrease in the absolute area of 

 the dorsal funiculus in passing from the lumbar to the thoracic 

 region. The horse, ox, bear, sheep, kangaroo, hog and lynx 

 show a very great decrease in the area of the dorsal funiculus 

 from the lumbar to the thoracic region (table 6) . The difference 

 in the area of the ventro-lateral funiculus in the two regions of 

 the above animals is very slight. This fact is expressed in an- 

 other form in columns 2 and 3, table 8b. The horse, for example, 

 has in the transverse section of the lumbar region a ventro-lateral 

 funiculus 2.31 times that of the dorsal funiculus, while in the 

 thoracic region, the ventro-lateral funiculus is 6.73 times the 

 dorsal. It is probable that in these animals an especially large 

 number of axones from the dorsal roots of the lumbar region 

 extend up the cord only a short distance and then terminate 

 around cell-bodies in the grey substance. 



