MOTOR PATHS IN THE CORD 243 



anterior fundamental fasciculus anteriorly external to the 

 column of Goll and internal to the posterior cornu. Its fibers 

 reach the cerebellum through the inferior peduncles, having 

 passed through the restiform bodies. 



Functions of the Columns. Remarks already made touch- 

 ing the direction of degeneration in the separate columns throw 

 some light upon the physiological function of the fibers in each. 



Motor impulses pass downward from the brain through cer- 

 tain fibers to the cells of the anterior cornua of gray matter in 

 the cord, and are sent thence through the spinal nerves to the 

 muscles. The paths in the cord conveying these impulses are 

 found to be the columns of Turck and the crossed pyramidal 

 tracts, and these are the only parts of the cord known so to act. 

 Impulses to the upper segment of the cord may be conveyed by 

 either of these columns, but impulses to the lower segment must 

 follow the crossed pyramidal tract, since the column of Turck 

 ceases to exist in the dorsal region. Only some 3-7 per cent, 

 of motor fibers from the cortex are thought to enter the columns 

 of Turck. The others decussate in the medulla and enter the 

 crossed pyramidal tracts. In any case motor impulses originat- 

 ing in the brain and so conveyed are manifested on the side 

 opposite their cerebral origin, since the fibers in both these 

 tracts decussate in passing downward. It is a well known patho- 

 logical fact that lesions of motor areas in the brain, or section of 

 one lateral half of the cord, are followed by paralysis on the side 

 opposite the lesion. 



Following a motor fiber (A, Fig. 77) through the anterior root 

 of a spinal nerve, it is found to originate from one of the large 

 multipolar cells (3) in the anterior cornu of gray matter. Around 

 these anterior horn cells (i, 2, 3, 4) arborize the end filaments 

 of fibers which have come down through the cord from the 

 brain. Some fibers have come down in the uncrossed pyramidal 

 tract (column of Turck) on the side opposite the cells, i, 2, 3, 4, 

 and crossed over to the same side through the anterior white 



