CH. XLV1IL] AFFERENT TRACTS TO THE CORTEX 



701 



tion unit (4) in the superficial layer of the grey matter. Its 

 intervening course from spinal ganglion to optic thalamus is, to save 

 confusion in the diagram, represented by a dotted line. The diagram 

 on the next page (fig. 439) fills in the details of the sensory path. 

 Beginning at the lower part of the diagram (fig. 439) on the right- 



FACE MUSCLE 



Fia. 488. Diagram of the principal efferent channels. 



hand side, we see one of the cells of a spinal ganglion. Its central 

 axon enters the cord, runs up the posterior column, and terminates in 

 one or other of the dorsal column nuclei (gracilis or cuneatus) ; the new 

 axons arising there, called arcuate fibres, cross the middle line and 

 ascend as fibres of the main fillet to the optic thalamus ; from which, 

 as we have seen, a new relay carries on the impulse to the cortex. 



