CHAP. XXX.] HIGHER CEREBRAL FUNCTIONS. 677 



been lost by a unilateral damage of the same definite and 

 extremely limited region of the Hemisphere. 



Thus it would follow, that the motor incitations suffic- 

 ing to call the articulatory centres into activity during 

 Speech, are accustomed, in the large majority of cases, to 

 emerge from the third frontal gyrus of the left side: though 

 in a small minority of persons it may happen that the 

 effective motor stimuli are wont to pass off instead from 

 the right third frontal gyrus. The halves of the bilateral 

 Articulatory Centres in the Pons, Medulla, and upper 

 part of the Spinal Cord are so welded together by com- 

 missures that each of them practically constitutes one double 

 Centre. And these may (after the manner of such bilateral 

 Centres) be incited to action by stimuli coming through the 

 Corpus Striatum either from the left or from the right 

 Cerebral Hemisphere though, as a matter of fact, as 

 above stated, such stimuli seem to reach it, in the large 

 majority of persons, from the left side of the Brain. 



But if bilaterally-acting muscles are always in associa- 

 tion with closely welded bilateral Motor Centres, and if 

 such Centres may generally be called into activity by 

 stimuli reaching them from either side or from both sides 

 simultaneously, then the habitual excitation of the Speech 

 Centres and their related muscles from the left side, must 

 be regarded as a remarkable peculiarity. 



There is, however, some reason for believing that if the 

 habitual outgoing channels of the left side are damaged 

 (so that Speech has been lost), the route for stimuli from 

 the right third frontal gyrus to the corresponding Corpus 

 Striatum may, under certain circumstances, be more effect- 

 ively opened up, so that the power of Speaking is after a 

 time regained. In such a case the stimuli would, of 

 course, impinge upon the right rather than upon the left 

 side of the lower bilateral Articulatory Centres. 



