358 THE SPINAL CORD. 



of the cord and, ascending along the surface of the cerebello-spinal 

 tract to the medulla, it winds inward dorsal to the restiform body 

 and terminates in the nucleus of the descending root of the vestib- 

 ular nerve. 



The lateral pyramidal tract (fasciculus cerebro-spinalis 

 lateralis} forms a considerable part of the lateral column of the 

 spinal cord (Figs. 102 and 103). It is covered, superficially, by 

 the cerebeUo-spinal tracts in the cervical and thoracic cord; but 

 in the lumbar and sacral cord it forms part of the surface. Its 

 deep surface is in relation with the posterior columna of gray 

 matter, the lateral fasciculus proprius and the marginal bundle. 

 The fibers composing it are axones of cell-bodies in the anterior 

 central gyrus of the cerebral cortex. They rise with those of the 

 anterior pyramidal tract, and the two run as one tract down 

 through the genu and anterior two-thirds of the occipital part 

 of the internal capsule, the middle three-fifths of the basis pedun- 

 culi, the anterior longitudinal fibers of the pons and the pyramid 

 of the medulla. In the medulla the two tracts separate. The 

 lateral tract, comprising four-fifths of the pyramid, decussates 

 with its fellow through the anterior median fissure, pierces the 

 anterior gray columna and descends with some uncrossed fibers 

 in the lateral column of the cord. It terminates in relation with 

 the cell-bodies within the posterior columna, according to Schafer, 

 Collier and others. The anterior tract follows the anterior median 

 fissure as already described. Both end chiefly in the gray crescent 

 opposite to their cortical origin. According to Marchi, ten or 

 twenty per cent, of the fibers remain uncrossed. The pyramidal 

 tracts are the cerebral motor tracts. By them motor and inhibitory 

 impulses are carried to the cord. In the outer part of the lateral 

 pyramidal area is found the crossed descending tract of the red 

 nucleus, the rubro-spinal tract (Pawlow). 



The Rubro-spinal Tract (Fig. 102). It extends as far as the 

 first lumbar segment and ends in the center of the gray crescent. 

 Its origin in the nucleus ruber, its crossing through the ventral 

 tegmental decussation (Foreli) and its course down the brain 

 stem have been described. The rubro-spinal tract is descending 

 in direction. 



