CH. XLIL] 



ROOTS OF THE SPINAL NERVES 



613 



derived from the fibres of the pyramidal tract P, which comes down 

 from the brain. 



According to Schafer's recent work, the pyramidal fibres really 

 terminate around the cells at the base of the posterior horn ; these 

 cells therefore act as intermediate cell-stations on the way to those 

 in the anterior horn. This is not shown in the diagram. 



A fibre of the posterior root is also shown ; this originates from 

 the cell G of the spinal ganglion ; the process of this cell bifurcates, 



Fio. 448. Course of nerve-fibres in spinal cord. (After Schafer.) 



one branch (B) passing to the periphery, where it ends in an arbor- 

 escence in the skin (S) ; the arrow by the side of this branch 

 represents the direction of conduction of the sensory impulses from 

 the skin. An arrow in the opposite direction would indicate the 

 direction of its growth. The other branch C passes into the spinal 

 cord, where it again bifurcates; the branch E, a short one, passes 

 downwards and ends in an arborisation around one of the small cells 

 Pj of the posterior cornu; from which a new axis-cylinder arises, 

 and terminates around one of the multipolar cells (4) of the anterior 

 horn. 



The main division D travels up in the posterior column of the 

 cord, and ends in grey matter at various levels. Some collaterals (5) 



