PBKIPHBEAL-lSrEKVE EOOTS, SPINAL GANGLIA, SPINAL COHD. 



347 



off from their ganglion-cells in the spinal ganglia. If one experimentally 

 divides these roots next to the cord, one produces exactly the same area of 

 degeneration. Just above the place of division hoth the external and the 

 internal posterior columns are degenerated; but farther iip, where new, 

 healthy root-fibers have entered, the latter lie external to those degenerated, 

 and, as one ascends, these affected fibers approach ever nearer the median 

 line. 



What we have just learned by an examination of the degenerated pos- 

 terior columns is reinforced by studying the development of the medullary 

 sheaths. It teaches, too, that there are at least two fiber-systems there: one 

 external, usually known as the prime bundle of the posterior columns; also 



Fig. 223. — Transverse section through the cervical cord of a newborn child. 

 The pyramidal tracts, minus meduUated fibers, appear translucent and clear. 

 The direct pyramidal tract extends far over into the antero-lateral column. 

 Wurgel-Zone, Eoot-zone. Kleinliirnseitenstrang-Uahn, Lateral cerebellar tract. 

 Grcnzschicht, Boundary layer or zone. Seitenstrang, Lateral column. Torder- 

 strang, Anterior column. Grnndbiindel, Ground-bundle. 



called the funiculus cuneaius, or column of Burdacli; and one internal, 

 called the 'funiculus gracilis, or column of Goll. In the normal cord of the 

 adult these two systems are separated from each other by a connective-tissue 

 septum only in the cervical portion, while in the lower sections they can only 

 then be distinguished when one or the other is diseased, when they differ 

 in color. The columns of Goll increase in volume from below upward, as far 

 as the lower dorsal cord, because they conduct portions of the continuously- 



