THE CENTRAL NERVOUS SYSTEM 



765 



D. C 



which has received the name of the direct pyramidal tract 

 pyramidal, because higher up in the medulla oblongata it forms 

 part of the pyramid ; direct, because it does not cross over at the 

 decussation of the pyramids, but continues down on the same 

 side. The direct pyramidal tract is only present in man and the 

 higher apes. 



(2) A tract of degenerated fibres in the posterior part of the 

 lateral column. This is the lateral or crossed pyramidal tract, 

 and is much larger than the direct. In the medulla it also lies 

 within the pyramid, but, unlike the direct pyramidal tract, it 

 crosses to the opposite side of the cord at the decussation. The 

 pyramidal tracts are also 



called cortico - spinal to 

 indicate their origin and 

 termination. 



(3) A tract of scattered % 

 degeneration lying along 

 the margin of the cord in 

 the anterior portion of 

 the antero-lateral column, 

 and partly overlapping 

 the tract of Gowers. It 

 is called the antero-lateral 

 descending tract, or tract 

 of Loewenthal. 



(4) The prepyramidal 

 (or rubro - spinal) tract, 

 or Monakow's tract, lying 

 immediately in front of the 



V.R 



FIG. 315. SCHEME OF CROSS-SECTION OF 

 SPINAL CORD (DONALDSON, AFTER LEN- 

 HOSSEK). 



On the left side only the afferent fibres are 

 shown ; the efferent fibres and the spinal cells 

 on the right side. D.R., posterior (dorsal) root ; 

 V.R, anterior (ventral) root ; C.P, crossed 

 pyramidal fibres ; C, direct cerebellar tract ; 

 A.L, antero-lateral tract ; D.C, posterior 

 columns. 



crossed pyramidal tract. 



(5) A small, comma- 

 shaped island of degene- 

 ration (comma tract) can 

 be followed downwards for a short distance in the middle of 

 Burdach's column. It is only seen in the cervical and upper 

 thoracic regions. 



When we have deducted the long ascending and descending 

 tracts which have been described, there still remains in the 

 antero-lateral column a balance of white matter unaccounted 

 for. This white substance, which does not degenerate for any 

 great distance either above or below a lesion, is called the antero- 

 lateral ground-bundle, and lies chiefly in the form of an incomplete 

 ring around the anterior cornu. It is believed to consist of 

 fibres (endogenous or proprio-spinal fibres) which run only a 

 comparatively short course in the cord, and serve to connect 

 nerve-cells at different levels. Some of these endogenous fibres 



