THE SPINAL CORD Ig 



VI. Lateral pyramidal tract contains fibres from the motor cortex of the opposite hemis- 

 phere which have come through the pyramid of the medulla and have decussated in the 

 medulla. These fibres descend and give off many collaterals, which, like their terminals, 

 turn inward and forward and terminate in a plexus of fine fibrils about the cells of the 

 anterior horn. They transmit voluntary motor impulses. 



VII. Lissauer's column is a small collection of white fibres of short course derived from 

 the posterior nerve root, which lies on the apex of the posterior horn. These fibres bifur- 

 cate on entering the column and pass up and down for a short distance, finally entering the 

 posterior horn, to which they give also many collaterals. The fibres terminate in brush-like 

 expansions about the cells of the posterior horn. 



VIII. The column of Burdach consists of three divisions: (i) the root zone near the pos- 

 terior horn, through which pass many of the posterior root fibres which bifurcate on entering the 

 zone and turn up and down, giving off numerous collaterals which enter the posterior horn 

 through the root zone ; (2) the median portion of the column which contains long fibres passing 

 from the posterior nerve root up to the cuneate nucleus of the medulla ; (3) a peripheral zone 

 containing other long fibres passing chiefly upward, but finally turning inward to the posterior horn. 

 Mingled among these three divisions are many association fibres whose origin, termination, and 

 collateral destination are in the posterior horns. These fibres are all sensory in their function. 



IX. The column of Goll consists wholly of long fibres which have entered the cord in 

 the posterior nerve roots of the sacral, lumbar, and lower dorsal regions and pass upward to 

 the nucleus gracilis of the medulla. They transmit sensory impulses. 



The constituents of the posterior nerve root require to be mentioned, a number of 

 different destinations being shown in the figures. These root fibres all bifurcate on entering 

 the cord, their divisions turning upward and downward. The downward division is short, and 

 soon turns into the gray matter, terminating in a brush-like expansion either in the posterior 

 or median gray matter about the intrinsic cells of the cord. The upward division is long, 

 and passes a varying distance toward the medulla, some fibres extending up the entire length 

 of the cord. Both divisions give off numerous collaterals which terminate like their true 

 ends. Some collaterals pass directly into the posterior gray horn and end there ; others pass 

 to the Clarke column of cells ; others pass by way of the posterior commissure to the other 

 half of the cord to terminate in the median gray matter; others pass directly through the 

 median gray to the anterior horns ending near the motor cells. These last are the paths 

 of reflex action. Impulses entering the cord thus are transmitted to the vicinity of the 

 intrinsic cells of the cord, which then take them up and send them on to the brain by 

 various tracts lying in the different columns already described. 



