592 PHYSIOLOGY OF THE NERVE CELL AND THE SPINAL CORD 



descending branch all of which taken together make up the bulk of the 



posterior columns of the cord. 



Some of the fibers of the posterior roots pass into the gray substance of 



the spinal cord, and either, like their collaterals, unite with cells in the an- 

 terior and posterior horns and in 

 the substantia gelatinosa, or unite 

 with the cells of Clark's column. 

 The latter fibers, however, are re- 

 garded by some authors merely 

 as collaterals. Other fibers of 

 these roots ascend throughout 

 the whole length of the spinal 

 cord without passing to the op- 

 posite side. They shift their 

 position somewhat in that they 

 come to lie nearer the mid line 

 the higher they go, so that the 

 median part of the posterior col- 

 umns in the higher segments of 

 the cord contains the prolonga- 

 tions of the posterior lumbosacral 

 and lower thoracic roots, while 

 the higher thoracic root fibers lie 

 outside these. At the cephalic 

 end of the cord these different 

 divisions become separated exter- 

 nally by a strong connective-tis- 

 sue septum; the median division 

 is then known as GolPs column, 

 the lateral as Burdach's column. 

 The fibers of Goll's column end 

 in the gracilar nucleus, those of 

 Burdach's column in the cuneate 

 nucleus. There is authority also 

 for the statement that fibers from 

 both columns pass directly to the 

 cerebellum and end there. 



The secondary afferent tracts 

 arise from the nerve cells with 

 which the fibers of the posterior 

 roots and their collaterals unite. 

 The following are the better 

 known among them: (1) Fibers 

 from the gracilar and cuneate 

 nuclei pass to the opposite side of 

 the medulla and continue forward 



in the fillet. (2) Long fibers arising from cells of the posterior horn traverse 



the anterior and lateral columns of the same and of the opposite sides as the 



FIG. 265. Diagram of the course of the sensory con- 

 ducting pathways after Striimpel. A, entrance 

 of the posterior sensory root fibers in the lum- 

 bar cord; gi, spinal ganglion; rp, posterior root. 



