156 



Ley ton and 8liorringtoii 



And we have obtained movements of neck and trunk respectively by 

 actual faradisation of the anterior wall of the fissure at those two places. 



The fissure being- of considerable depth, exceeding 12 mm. in several 

 places both in the chimpanzee and orang (we have not explored it in the 

 gorilla), the amount of excitable area contributed by it to the motor field 

 of the cortex in the anthropoid is quite large. Fig. 15 (vide infra, p. 171) 

 illustrates this. It is schematic, but not wholly so ; it was prepared from 

 a chimpanzee hemisphere, in which a number of points of the buried motor 

 cortex were actually determined by faradisation, and the depth to which 

 the fissure was excitable was tested at a series of places. With these as 



'"\tA''7^ 5^)\ 



Fig. 6.— a, chimpanzee 11; left hemisphere, showing lesponses obtained at opened-up parts of 

 some sulci. On the free face of the convolutions some of the responses evoked there are marked 

 into the map to serve for orientation. B, chimpanzee 15 ; right hemisphere reversed, re- 

 sponses from opened-up parts of sulci and from free surface. The animal was of the variety 

 Troglodytes calvus, and very intelligent. 



a basis, the rest of the deep contour is given by interpolating determina- 

 tions obtained in other chimpanzee hemispheres. In our observations the 

 posterior boundary of the motor cortex lying hidden in sulcus centralis 

 seems to be more abruptly and sharply delimited than is the anterior 

 margin of it, lying largely on the free surface of the hemisphere. 



The motor responses yielded from points buried in sulcus centralis 

 corresponded for the most part rather closely with the motor responses 

 yielded by the free surface of centralis anterior of about the same 

 horizontal level. A good deal of the local area for pinna seems to lie 

 buried in the sulcus close below inferior genu, and we have obtained pinna 

 movements from the anterior wall of the sulcus at that place in specimens 

 where we could not elicit them from the free surface of the gyrus. The 



