THE SPINAL CORD. 41 I 



taining nerve-fibers which come from the pyramids of the medulla. 

 The majority of the pyramidal fibers cross from one side of the cord 

 to the other in the lower portion of the medulla, at the crossing of 

 the pyramids, and form a large bundle of nerve-fibers found in each 

 lateral column, which will receive attention later. Some of the 

 pyramidal fibers descend into the cord on the same side, to cross to 

 the opposite side at different levels in the cord. These latter fibers 

 constitute the narrow median zone, on each side of the anterior 

 median fissure previously mentioned, forming the anterior or direct 

 pyramidal tract, or the column of Tiirck. Between the direct 

 pyramidal tract and the anterior horn lies the anterior ground 

 bundle. 



In the lateral columns are found a number of secondary col- 

 umns, which may now be mentioned. In front of and by the side 

 of the posterior horn in each lateral column lies a large group of 

 nerve-fibers, forming a bundle which varies somewhat in size and 

 shape in the several regions of the spinal cord, but which has in 

 general an irregularly oval outline. These nerve-fibers are the 

 pyramidal fibers, previously mentioned, which in the lower part of 

 the medulla cross from one side to the other, and for this reason 

 are known as the crossed pyramidal fibers, forming the crossed 

 pyramidal columns. External to these columns and to the poste- 

 rior horns, and extending from the posterior horns half-way around 

 the periphery of the lateral columns, lie the direct cerebellar col- 

 umns, consisting of the neuraxes of the cells of the columns of 

 Clark, which have an ascending course. Lying just external to and 

 between the anterior and posterior horns is a somewhat irregular 

 zone, the mixed lateral column, containing several short bundles 

 of fibers, the anterior of which are probably motor ; the posterior, 

 sensory. In. the ventrolateral portions of the lateral columns, 

 between the mixed lateral and the direct cerebellar columns and 

 extending as far backward as the crossed pyramidal columns, lie 

 two not well-defined columns, known as the ascending anterolat- 

 eral or Gowers's columns and the descending anterolateral col- 

 umns ; the former are nearer the outer portion of the cord. 



In the posterior column we distinguish a median and a lateral 

 column. The former lies along the posterior median septum, and 

 may even be distinguished externally by an indentation ; its upper 

 portion tapers into the fasciculus gracilis. This is the column of 

 Goll, and it contains ascending or centripetal fibers. The lateral 

 tract lies between the column of Goll and the posterior horn, and 

 is known as the column of Burdach, posterior ground-bundle, or 

 posterolateral column. It contains principally the shorter tracts, or 

 bundles of longitudinal fibers connecting the adjacent parts of the 

 spinal cord with one another. 



Many of the nerve-fibers of the posterior column are the neu- 

 raxes of spinal ganglion cells which enter the spinal cord through 

 the posterior roots. The cell-bodies of the spinal ganglion or sen- 



