746 



COURSE OF THE TRACTS FOR CONSCIOUS SENSATION. 



sensibility pass through the fillet and the ventral portion of the reticular 

 formation. 



The connections of the posterior roots of the nerves of the spinal cord, 

 through which sensibility is transmitted, are, according to recent inves- 

 tigators, as follows: 



The posterior columns transmit impulses from the afferent poste- 

 rior roots upward. A lateral and a median bundle can be recognized 

 in the posterior root. The median bundle of each afferent root in its 

 course upward in the posterior column is generally situated to the outer 

 side close to the posterior horn (Fig. 257, 2). Each root as it enters at a 

 higher level (i) displaces further and further inward the fibers derived 

 from the roots situated at a lower level. Therefore, the sensory fibers com- 

 ing from the lower extremities are, in the cervical cord, situated princi- 

 pally in the columns of 

 Goll, while the columns 

 of Burdach still contain 

 many fibers from the 

 upper extremities. As- 

 cending, the fibers of 

 the posterior columns 

 terminate above in the 

 medulla oblongata, in 

 the formations (nuclei of 

 the gracile and cuneate 

 columns) known as the 

 nuclei of the posterior 

 columns. From these 

 nuclei many fibers pass 

 into the fillet (L) of the 

 opposite side. Other 

 fibers pass to the cere- 

 bellum. The lateral 

 fibers, coarse and fine, of 

 the posterior root (3, 4) 

 enter the delicate plexus 

 of the posterior horn, in 

 which the ganglion-cells 

 of the posterior horn are 

 lodged. From the plexus 

 of the posterior horns 

 there arise numerous 



fibers that pass forward through the gray matter, undergo decussa- 

 tion, and then continue toward the cerebrum in the anterior and lateral 

 columns. At a higher level these fibers, with their original accom- 

 paniments, reunite (at L), so that almost all of the posterior root-fibers 

 (decussated) again lie together in the fillet or the intermediary layer of the 

 The further course of these fibers to the cerebral cortex is dis- 



FIG. 256. Course of the Motor and Sensory Paths through a Trans- 

 verse Section of the Spinal Cord: i, Anterior pyramidal tract; 

 3, lateral pyramidal tract; 4 and 5, decussating sensory paths in 

 the spinal cord; 6, ascending sensory paths not decussating in the 

 spinal cord; 7, sensory path to the columns of Stilling and Clarke, 

 and thence undecussated upward through the lateral cerebellar 

 tracts; 2, origin of a motor fiber as a neurite from a ganglion-cell 

 of the anterior horn. 



olive. 



cussed on p. 80 1. A portion (5) of the fibers of the posterior roots, which 

 are not connected with the cells of the spinal ganglia, terminate in the 

 cells of the column of Stilling and Clarke, which are at the same time 

 the trophic centers for those fibers. The fibers turn outward from the 

 .s and ascend in the lateral cerebellar tract. Their further course is 

 upward to the restiform body, and thence to the cerebellum. These 



