THE TRACTS 



269 



which, however, are collected together again in the medulla, 

 where they form the ventrally placed 'pyramids. At the 

 lower end of the medulla the great majority of the fibres 

 cross over {decussation of the pyramids) and occupy an 

 area in the lateral columns of the cord (crossed pyramidal 

 tract) (Fig. 43, 1). They terminate at different levels by 

 passing into the grey matter and arborising around cells in 

 the anterior horn and at the roots of the posterior horn. 



s/^.L 



Fig. 43. — Diagram sho^nng the ascending (right pide) and the de- 

 scending (left side) tracts in the spinal cord (from Schafer's Essentials 

 of Histology). 



A few fibres {uncrossed lateral pyramidal tract) pass into 

 the lateral columns of the same side. 



Some fibres {direct pyramidal tract) pass into the anterior 

 columns of the cord on the same side (2). 



2. Prepyramidal or Rubrospinal Tract {Bundle of Mona- 

 how). — This bundle arises in the red nucleus of the mid- 

 brain, through which it gains connection with the cerebellum. 

 In the cord the fibres occupy a position anterior to the 

 pyramidal tract (4) and end in the grey matter, joining 

 the anterior and posterior horns. 



3. Tecto-spinal and Olivo-spinal Tracts {Bundle of 



