THE ROOTS OF THE PERIPHERAL NERVES, ETC. 



161 



anterior column can no longer be seen, because its fibres are lost 

 in the regions from which the motor nerves issue. In Fig. 100 

 the points 7 and 7' give a general idea of the pyramidal tract at 

 different levels of the spinal cord. 



The examination of spinal cords affected by secondary 

 degeneration throws still more light upon their structure. If 

 we make sections of spinal cord whose continuity has been in- 

 terrupted in the dorsal portion by pressure or any other violence, 

 we shall find, as might be expected from what has already been 



FIG. 98. 



Cross-section through the cervical cord of a newborn child. The pyramidal tracts 

 without medullary fibres appear glistening and clear. The direct pyrarui'dal tract iu the 

 anterior column encroaches markedly upon the antero-lateral column. 



Grenzechicht, Limiting layer. 

 G-rundbUndel. Ground-lmndle. 

 Klrinhirnxeitenstrutifj-Bfiltn, Lateral cerebellar tract. 



Sf.itenstrang, Lateral column. 

 Viirrlrrstranij, Anterior column. 

 Wursel Zone, Zone of the roots. 



said, that the pyramidal tracts on each side have become degen- 

 erated downward. But there is also a degeneration upward from 

 the level of the injury. At first this degeneration occupies the 

 whole area of the posterior column, but at a point a few seg- 

 ments higher up it is limited to that part of the column which 

 lies along the posterior median fissure. In such specimens we 

 can easily divide the posterior column into an inner and an 

 outer one. The parts affected by this ascending degeneration 

 (which extends into the oblongata) are fibres of the posterior 



