352 ANATOMY OF THE CENRTAL NEEVOUS SYSTEM. 



In the adult cord these relations are not discoverable. One must make use of 

 embryonic cords, in which the pyramidal fibers are as yet non-medullated, then stain 

 with silver after Golgi's rapid method, and prepare longitudinal and diagonal sec- 

 tions. In such sections one may often trace the collaterals, given off at right angles 

 from the pyramidal fibers and entering the gray matter (cf. Fig. 227). These branches 

 must later be medullated; for, in eases of degeneration of the pyramids, one finds 

 invariably the corresponding ventral horn poorer in medullated fibers than normally 

 (Furstner). The same branches show very distinctly, when one succeeds in staining 

 them with osmium during their degeneration (Fig. 228, sec. 5). 



Many difficulties oppose themselves to the study of the relations of the 

 posterior nerve-roots. Their fibers all, or nearly all, divide, immediately 

 after entering the cord, into an ascending and a descending branch. Prom 

 these arise numerous collaterals that pass partly to the gray matter, partly 

 into the posterior columns {vide Fig. 227). 



The fate of single divisions of the roots is very varied; their relations 

 are extremely complicated, so far as is novs^ knovifn. In view of this, it will be 

 well to refer frequently to Fig. 227 while considering what follows. This 

 figure represents what is actually known. It implies that which concerns 

 the multitude of fibers, and not any single section. Its purpose is merely 

 to elucidate the text. 



In a cross-section of the spinal cord one recognizes that the posterior 

 roots, at their entrance, are definable into at least five parts. The most 

 median bundles (1), mainly consisting of large fibers, nearly all enter the 

 posterior columns immediately (posterior root-zone). Here, as we have 

 learned, they turn upward toward the brain. The behavior of these roots, 

 upon secondary degeneration following their section, teaches that those 

 bundles which enter directly into the dorsal column are afterward pushed 

 toward the median line by those entering at a higher level, so that the 

 caudal root-fibers occupy above a position near the middle line,' in GoU's 

 column, and Burdach's column is largely made up of such fibers just enter- 

 ing and ascending diagonally (Fig. 28). We have also learned that, while 

 running thus diagonally, there are fibrils continually being given off, which 

 enter the gray matter. 



Immediately after entering the cord, before the fiber turns cephalad, a 

 branch is given off which turns caudad. Its course is now better known, 

 since examinations of fresh secondary degenerations were made by the 

 Marchi method (SchafEer, Lowenthal, and others). 



In general, the traces of secondary degeneration on examination by 

 this method appear so much more complicated than as represented in the 

 preceding chapter that it will be well to examine the accompanying figures 

 from cases described by Hoche (Fig. 228). 



The place of compression lies in the region of the seventh dorsal vertebra. The 

 degeneration at that point (3), as indicated by the osmium-blackened points, is 



