CONNECTIONS OF THE LONG PATHS OF THE CORD 871 



degenerated only at its outer border. Higher up degeneration will 

 be found to have involved the whole of the postero-median column, 

 and to have cleared away altogether from the postero-external. 

 The degeneration in the column of Goll may be traced along the 

 whole length of the cord to the medulla, although the number of 

 degenerated fibres diminishes as we pass upward. The explanation 

 of these appearances 'is as follows : It may be 

 seen in preparations of the cord impregnated by 

 Golgi's method that the fibres of the posterior 

 roots soon after their entrance into the cord 

 divide into two processes, one of which runs up 

 and the other down in the posterior column, or 

 in the adjoining portion of the posterior horn. 

 From both of these collaterals are given off at 

 intervals to the grey matter. The descending 

 branches run downwards only for a short dis- 

 tance, and the degeneration in the comma tract 

 seen after section 

 of the cord is due 

 to the division of 

 these branches. 

 Many of the as- 

 cending branches 

 pass up for a short 

 distance in the 

 postero-external 

 column, sweeping 

 obliquely through 

 it to gain the tract 

 of Goll. In this 

 tract some of them 

 run right on to 

 the medulla ob- 

 longata, to end by 

 arborizing among 

 the cells of the 

 nucleus gracilis. 

 Other fibres, both 

 of Coil's and of 

 Burdach's tract, 

 end at various 

 levels in the cord, 

 their collaterals, and ultimately the main branches themselves, 

 coming into relation with nerve-cells in the grey matter. When the 

 cervical posterior roots are cut, many of the degenerated fibres 

 remain in Burdach's column up to the medulla, where they terminate 



Fig. 348. Diagrams 

 of Degeneration at 

 Different Levels in 

 the Cord after Sec- 

 tion of a Number of 

 Posterior Roots of 

 Nerves forming the 

 Lumbo-Sacral Plex- 

 us (Mott). 



Fig. 349. Branching of Posterior 

 Root-Fibres in Cord (Donald- 

 son, after Cajal). Collaterals, 

 Col, are seen coming off from 

 the two main branches of the 

 root-fibres, DR, and ending in 

 arborizations. CC, cells in the 

 grey matter of the cord, whose 

 axons also give off collaterals. 



