LOCALISATION OF FUNCTION. 



253 



corresponding hemisphere. In this crude manner the 

 impulses may be pictured as distributing themselves 

 within the central system by means of the incoming 

 fibres and their colla- 

 teral branches, aided 

 by the central cells. 

 The expansion of the 

 nucleus of a motor 

 nerve through several 

 segments is, by com- 

 parison, centralisa- 

 tion in a high degree 

 when contrasted with 

 the manner in which 

 a sensory pathway 

 thus extends itself 

 over a large part of 

 the central system. 

 It is well to bear in 

 mind that the cranial 

 nerves, so far as they 

 mediate afferent im- 

 pulses, have, like the 

 sensory nerves of the 

 spinal cord, primary 

 centres at the points 

 where theyterminate 

 in the axis, and that 

 from those primary 

 centres they esta- 

 blish secondary con- 

 nections with the 

 cerebral hemispheres. 



FIG. 51. Schema showing the path- 

 way of the sensory impulses. On 

 the left side, S, S', represent afferent 

 spinal nerve fibres ; C, an afferent 

 cranial nerve fibre. This fibre in 

 each case terminates near a central 

 cell, the neuron of which crosses the 

 middle line, and ends in the opposite 

 hemisphere. (Van Gehuchten.) 



They resemble the 



sensory nerves of the spinal cord also in the fact that the 



