THE BRAIN AND SPINAL CORD 111 



have shown that the axons of the white matter oeeur in strands of 

 well-defined location. The axons of the dorsal columns carry sen- 

 sory impulses up the cord; those of the ventral columns carry motor 

 impulses down the cord; and the lateral cohmins are suhdi\ided 

 into tracts, some of which are sensory and some motor. The fjray 

 matter of the cord consists of neurogHa; axons entering from the 

 columns; entire short neurons; cytons, dendrites, and the initial 

 portions of axons which extend further beyond the gray matter into 

 the ventral roots of spinal nerves and on out into such nerves. The 

 neurons of the gray matter are multipolar in type and have already 

 been described. Axons of some gray matter neurons extend out 

 into the white matter and are incorporated as part of a white 

 column. 



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