THE CENTRAL NERVOUS SYSTEM 



677 



(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. 



(3) A tract of scattered degeneration lying internal to and 

 partly overlapping the tract of Cowers. It is called the 

 antero -lateral descending tract. 



(4) A small comma-shaped island of degeneration (comma 

 tract) can be followed 



downwards for a short D c 



distance in the middle of 



Burdach's column. It is 



only seen in the cervical 



and upper thoracic re- 



gions. 



When we have de- 

 ducted the long ascend- 

 ing and descending 

 tracts which have been 

 described, there still re- 

 mains, both in the an- 

 terior and in the lateral 

 column, a balance of 

 white matter unac- 

 counted for. This white 

 substance, which does 



D. P 



FIG. 240. 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 t posterior (dorsal) root ; 

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

 pyramidal fibres ; C, direct cerebellar tract ; 

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

 columns. 



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 



which run only a comparatively short course in the cord, and 



serve to connect nerve-cells at different levels. 



The next question which arises is : How are the long 

 tracts connected below, i.e., with the periphery, and above, 

 i.e., with the higher parts of the central nervous system ? 

 The answer to this question, partly derived from clinical 

 records and partly from experimental results, is in the case 



