THE SPIRAL CORD 



839 



Another tract, usually described as belonging to the lateral column, but 

 functionally more intimately related to the' sensor neurone system of the dorsal 

 column is the fasciculus marginalis (of Spitzka and Lissauer, described on 

 page 840). 



The great majority of the axones constituting the dorsal column are the afferent 

 (sensor) axones arising from the spinal ganglion cells, entering the cord by the 

 dorsal roots. These dorsal root axones bifurcate in the region of the dorsal 

 horn, one branch ascending a little obliquely at first, then vertically, while the other 

 branch takes a similar downward course for a shorter distance (Fig. 613). As 

 additional groups of fibres are contributed by each 

 successive dorsal nerve root the mass of white 

 substance in the dorsal column accumulates as 

 the cord is ascended, though it must be noted that 

 not all of these afferent fibres traverse the whole of 

 the cord above, but end in relation with cells in 

 the gray substance at various levels. The succes- 

 sive accessions of afferent fibres are disposed in 

 a laminated manner so that the lumbar fibres 

 come to lie laterad of the sacral bundle, the 



thoracic laterad of the lumbar, and so on as the, 

 cord is ascended. A section of the cord at its 

 highest level would therefore traverse a collection 

 of bundles derived from all of the dorsal nerve roots 

 of the cord, arranged as shown in Fig. 612. 



In the upper segments of the cord it is possible 

 to distinguish a division of the dorsal column into 

 two principal fasciculi owing to the presence of 

 a distinct connective-tissue septum which passes 

 into the substance of the dorsal column along the 

 dorsopara median groove. These fasciculi are 

 termed the fasciculus gracilis, or Goll's column, and 

 the fasciculus cuneatus, or Burdach's column; in the 

 consideration of the external morphology of the 

 cord, these have already been referred to as the 

 funiculus gracilis and funiculus cuneatus, respec- 

 tively. 



It has been noted that even in the fresh cord, 

 when sectioned, the gracile bundle has a different 

 tinge and stains more deeply with carmine than 

 does the cuneate bundle. 



The caudal or descending branches of the bifur- 

 cate dorsal root axones are considerably shorter 

 thanthe ascending; branches. They terminate in 



Sacral 

 nerves 



FIG. 611. Formation of the fascic- 

 ulus gracilis. Spinal cord viewed from 

 behind. To the left, the fasciculus 

 gracilis is shaded. To the right, the 

 drawing shows that the fasciculus 

 gracilis is formed by the long fibres of 

 the posterior roots, and that in this 

 tract the sacral nerves lie next the 

 mesal plane, the lumbar to their outer 

 side, and the thoracic still more later- 

 ally. (Poirier.) 



the grav substance in relation with its cells and. 



by numerous collaterals which are shorter or longer 



and given off at various intervals, serve to asso- 



ciate different levels of the cord. Some of these 



collaterals cross the median line in the dorsal (gray) 



commissure to come into relation with neurones of the opposite side. Certain 



of the longer descending branches show a tendency to collect into a feebly marked 



bundle along the mesal border of the cuneate fasciculus, called, because of its 



outline in trans-sections as seen in cases of descending degeneration from 



injury at a higher level the comma tract of Schultze. A similar bundle, situated 



.along the dorsal septum, best demonstrable in the lumbar cord, and with its fellow 





