XXX.] SPINAL CORD. 331 



ftifucttltis cuneatuSj or column of Bur dad i. In the upper part of the 

 cord these two tracts are mapped off from each other by a septum 

 of connective tissue (fig. 317). 



Tlic postero-wtfrnal tract is composed chiefly of rather small fibres, 

 derived from the fibres of the posterior roots and fibre of the pos- 

 tero-lateral column. They end above in grey matter in the nucleus 

 gracilis of the bulb. 



The postero-lateral trad is chiefly composed of nerve-fibres of the 

 posterior roots which run in it a certain distance before they pass 

 into the grey matter and Goll's column. They end in grey matter 

 in the cord and in the nucleus cuneatus of the bulb. 



In the postero-lateral column is a small zone which undergoes 

 descending degeneration, but only for a short distance, after section 

 of the cord the so-called comma trad. 



LixMuer's Tract, or " marginal bundle" lies near the entrance of 

 the posterior roots, either in the lateral column or postero-external 

 column. It is derived directly from the fibres of the posterior roots. ^ 

 It undergoes ascending degeneration. 



The antero-lateral column contains a large tract the crossed 

 pyramidal tract which lies external to the posterior half of the 

 grey matter, and in the greater part of its course is separated from 

 the surface of the cord by the direct cerebellar tract. It consists 

 of fibres descending from the central areas (motor,) of the cerebral 

 cortex, which have crossed at the decussation of the pyramids in 

 the bulb. It consists of moderately large and some small fibres. 

 Its fibres end by breaking up into fibrils, which form arborisations 

 around the nerve-cells in the anterior cornu. It gradually 

 diminishes in size as it passes down the cord, and can be traced as 

 far as the origin of the 3rd or 4th sacral nerve, where it reaches the 

 surface. 



The direct pyramidal tract or column of Turck bounds the 

 anterior median fissure, and consists of fibres coming from the 

 motor areas of the cerebral cortex, which do not cross at the bulb. 

 This tract gets smaller, and gradually disappears about the mid- 

 dorsal region. Its fibres perhaps cross in the cord. These two arc 

 descending tracts. 



Beginning at the lower dorsal region, and increasing in size as it 

 passes upwards, is a tract lying external to the crossed pyramidal 

 tract the direct cerebellar or dorso-lateral tract which con- 

 sists of large fibres derived from the cells of Clarke's column, 

 which pass up to the cerebellum, and enter it on the same side by 

 its inferior peduncle or restiform body. Near the surface of the 

 cord, and lying more anteriorly, is a tract which extends ventrally 

 into the anterior column the antero-lateral awndinrj tract of 

 Gowers. Sometimes the term ventro-lateral is applied instead of 



