THE NERVOUS SYSTEM 1329 



they arise to the opposite side. In the case of the crossed pyramidal 

 tract the crossing takes place in the lower part of the medulla 

 oblongata. In the case of the direct pyramidal tract the crossing 

 takes place in the ventral median fissure of the spinal cord along 

 the course of the tract. 



The uncrossed lateral pyramidal tract consists of a few fibres 

 which descend from the corresponding pyramid of the medulla 

 oblongata into the lateral column of the same side, where they mix 

 with the fibres of the crossed lateral pyramidal tract. It differs 

 from the crossed lateral, and direct, pyramidal tracts, inasmuch as 

 its fibres never cross to the opposite side. It is therefore a direct 

 motor path from the Rolandic motor area of the cerebral cortex of 

 the same side. 



The anterior marginal or ground-bundle of Lowenthal {fasciculus 

 anterior proprius B.) or tractus vestihulo-spinalis is situated in 

 the anterior column, where it lies superficially. Its fibres are 

 derived from the cells of the nuclei of Deiters in the medulla 

 oblongata, chiefly on the same side as the bundle. These nuclei 

 receive fibres of the corresponding vestibular nerve, and are 

 closety related to the vestibular nuclei. The bundle descends 

 through the meduUa oblongata and ventral column of the spinal 

 cord as low as the lumbar region, and its fibres terminate in the 

 anterior cornu of grey matter aroimd the ventral or motor cells. 

 The nucleus of Deiters and the vestibular nucleus, of either side, 

 are connected with small grey nuclei which lie in the white matter 

 of the cerebellum, and in this manner an indirect connection is 

 established between the cerebellum and the ventral or motor-cells 

 of the ventral grey cornu of the spinal cord, as foUows : The grey 

 nuclei within the cerebellimi are connected with the nuclei of 

 Deiters, and the axons of the cells of Deiters represent the origin of 

 the fibres of the anterior marginal or ground-bundle, which fibres 

 terminate around the ventral or motor-cells of the ventral grey 

 cornu of the spinal cord. 



The prepyramidal or rubrospinal tract, or bundle of Monakow, is 

 situated in the lateral column, on the ventral aspect of the crossed 

 pyramidal tract. Its fibres are chiefly derived from the red nucleus 

 of the tegmentum or dorsal part of the cms cerebri of the opposite 

 side, and they are regarded as terminating in the dorsal part of the 

 ventral cornu of grey matter .- 



The bulbo-spinal tract, or bundle of Helweg, is confined to the 

 cervical region of the cord, and is triangular. Its fibres are 

 regarded as arising in the medulla oblongata behind the olive, but 

 their mode of termination is not known. They lie near the surface 

 of the cord opposite the lateral cornu of grey matter. 



Ascending Tracts.— The dorsal spino-cerebeUo tract, or direct 

 cerebellar tract of Flechsig {fasciculus cerebello-spinalis B.), is 

 situated in the lateral colimin. It lies in front of the dorso-lateral 

 sulcus, between the crossed pyramidal tract and the outer surface 



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