412 HISTOLOGY 



iculi of rodents but in the lateral and ventral funiculi of the human cord. 

 In man most of these fibers, in descending from the brain, cross to the 

 opposite side in the medulla oblongata and complete their descent in the 

 lateral funiculus of the cord, where they form the lateral cerebro-spinal 

 fasciculus; they terminate in relation with motor cells on the same side 

 of the cord. A smaller number of these fibers fail to cross in the medulla, 

 and descend in the ventral funiculus as the ventral cerebro-spinal fascicu- 

 lus; these fibers cross to the opposite side in the cord, passing through 

 the ventral commissure, and then terminate in relation with the motor 

 cells. Thus the cerebro-spinal fibers all cross, but the decussation may 

 take place either in the medulla or in the cord. 



The fibers which convey tactile stimuli to the brain enter by the 

 dorsal roots and pass into the gray substance of the cord, where they 

 terminate in relation with small cells dorsally placed. Fibers from these 

 cells cross to the opposite side of the cord through the gray commissure, 

 and then enter the white substance of the lateral funiculus in which they 

 ascend to the brain. One of these fibers and a descending fiber of the 

 lateral cerebro-spinal fasciculus are shown in the diagram, Fig. 123, p. 131. 



In addition to fibers of the long tracts, such as pass between the spinal 

 cord and the hemispheres, cerebellum and other parts of the brain, the 

 ventral and lateral funiculi contain fibers which emerge from the gray 

 substance of the cord at one level and re-enter it at another, thus placing 

 the cells at different levels in communication. The fibers of these " ground 

 bundles" or fasciculi proprii generally remain close to the gray substance. 

 Their entrance and exit along the lateral concavity of the gray substance 

 causes it to be broken up into zformatio reticularis (Fig. 424). 



The dorsal funiculi in the upper part of the cord are each subdivided 

 into a slender medial fasciculus gracilis (column of Goll) and a wider 

 lateral fasciculus cuneatus (column of Burdach), which are partially sepa- 

 rated from one another by a septum. These fasciculi are composed 

 chiefly of the fibers of "muscle sense," which enter by the dorsal roots 

 and divide into ascending and descending branches. Many of these pass 

 into the gray substance of the cord after traveling varying distances in 

 the dorsal funiculi. Some of the ascending fibers, however, are very long 

 and extend to the medulla oblongata, gradually approaching the median 

 septum in their ascent. The gracile fasciculi are composed of these long 

 ascending fibers, and since they are not segregated in a distinct bundle in 

 the lower portion of the cord, this fasciculus is absent from the lumbar 

 region. In addition to the fibers of muscle sense, the dorsal funiculi con- 

 tain some fibers of general sensation, a limited number of association 

 fibers, and others. 



The description of the fiber tracts in the spinal cord and brain is the 

 subject of special text-books; they are briefly and clearly described by 



