The Excitable Cortex of the Chimpanzee, Oraii^-rtan. and Corilla 159 



Remarks on the Grouping of the Responses 

 of the Motor Cortex. 



An occurrence met in some of our <*xporimonts was that in the course 

 of examination of gyrus centralis anterior some small art-a of its surface 

 might exist whence the faradisation failed to evoke responses. An in- 

 stance is figured in fig. 2, B, close to the genu inferius of sulcus centralis. 

 The appearance of the cortex at such a place would reveal to inspection no 

 obvious circulatory disturbance : nor so far as we were aware had any 

 damage been inflicted there. But in many experiments the whole motor 



Fig. 8.— Orang 2. A, left hemisphere; B, right hemisphere reversed for comparison with A. 

 Some only of the responses obtaineil are entered ou the map. 



field systematically explored revealed no obvious gap in it. Beevor and 

 Horsley in the brain of the orang they stimulated met with relatively 

 large and numerous gaps of this kind, and supposed them characteristic 

 of the motor area of the anthropoid brain. Franz records meeting with 

 small areas not yielding responses in the motor field of the macaque 

 monkey. In our experience, a return later in the experiment to the small 

 area which had not yielded responses found it still unyielding of response. 

 Such an area was on several occasions ascertained to have no counterpart 

 that we detected in the hemisphere of the opposite side. Nor were the 

 places of occurrence of such seemingly non-stimulable gaps the same in 

 hemispheres of different individuals, a finding in conformity with that of 

 Franz in macacus. In our experience, such a gap was perhaps less infre- 

 quent than elsewhere about the region where face area meets arm area. 

 VOL. XL, NO. 2. — 1917. H 



