CIT. XLTT.] 



DEGENERATION TRACTS 



017 



of the cord towards the lateral column. These originate from the 

 posterior longitudinal bundle of the medulla oblongata, and from 

 other sources to be described later. They end by synapses in the 

 anterior horn. 



(4.) The prepyramidal tract (Monakow's bundle). This is situated 

 just in front of the crossed pyramidal tract. Its origin is in the cells 

 of the red nucleus in the mid-^rain. Its fibres end by arborisations 

 in the grey matter about the middle of the crescent. 



(5.) Bundle of Helweg. The exact origin and destination of these 

 fibres are not known : they can be traced from the neighbourhood of 

 the olivary body in the medulla oblongata, and pass down in the 

 anterior part of the lateral column in the cervical region. 



(6.) Short tracts in the posterior column. These are (a) the Comma 

 tract ; though this degenerates downwards, it is in reality a sensory 

 tract, being composed, as we have already seen, of the branches of 

 the entering posterior root-fibres which pass downwards on entering 

 the cord. It is only found for a comparatively short distance below 

 the actual lesion. (b) Septo-marginal fibres; these are few in 

 number, and are mainly found near the median fissure, where they 

 constitute the oval bundle, and near the posterior surface, where they 

 form the median triangle bundle. These are doubtless short associa- 

 tion tracts, and are mixed with others, especially in the ventral part 

 of the posterior column, which have an " ascending " course. 



Tracts of Ascending Degeneration (fig. 451). 



(I.) Postero-medial column, or column of G-oll. This consists of fibres 

 derived from the posterior roots of the sacral, lumbar, and lower 



s tract 



Direct cerebellar 

 tract 



FIG. 451. Tracts of ascending degeneration, shown on one side of the cord only. (After Schafer). 



thoracic nerves. These fibres enter the postero-lateral column, and 

 gradually pass towards the mid-line, as already explained. They 



