162 



LECTURES ON THE CENTRAL NERVOUS SYSTEM. 



roots, which have been divided from their ganglion-cells in the 

 spinal ganglia. If we divide these posterior roots experiment- 

 ally just outside the spinal column (Singer) we shall produce an 

 exactly similar degeneration. Just above the divided point both 

 the outer and the inner posterior columns are degenerated; 

 farther up new and healthy root-fibres enter and arrange them- 

 selves to the outside of the injured ones, so that the area of 

 degeneration is gradually pushed farther and farther toward the 



median line as we pass higher up in the cord. 

 The study of the development of the 

 medullary sheaths confirms the conclusion 

 reached by the investigation of secondary 

 degeneration. It teaches that there are here, 

 at least, two sets of fibres, an outer one, 

 ordinarily called the fundamental bundle of 

 the posterior column, also called wedge-shaped 

 column, or column of Burdach, and an inner 

 one, which is called the slender column 

 (funiculus gracilis), or GolPs tract. In the 

 normal adult cord the two divisions of the 

 posterior column* are separated from each 

 other by a septum of connective-tissue only 

 in the cervical region. In sections made 



O 



lower down we can only distinguish them 



Secondary ascending i i i 



and descending degenera- wllCll O11C Ol* the otllCl' IS degenerated, and 

 tion following a trans- 



to^Sji*" So^ TO therefore is differently stained. Goll's tract 



eion. (After Striimpell.) / , i 10 



increases in size from below upward as lar as 

 the upper dorsal region, probably because portions of the pos- 

 terior nerve-roots are continually entering it on their way to the 

 medulla oblongata. It is not improbable that still further sub- 

 divisions of the posterior columns will be made in the future. 

 The manner of extension of certain diseases, and occasional rare 

 forms of secondary degeneration, lead us to anticipate this. 



" 



* Funiculus cuneatus and funiculus gracilis in Fig. 89 B, also called postero-external and 

 postero-internal columns. 



