The Excitable Cortex of the Chimpanzee, Orang-Utan, and Gorilla 205 



and explored by faradisation from point to point. It nowhere yielded any 

 regularly recurring results as far as could be seen except, in upper and fore 

 part, opt'uing <»l" eyon; in most parts of it excitation was not followed by 

 any visible result whatever. The larynx was kept under laryngoscopic 

 examination for the greater part of the time that this area was being 

 explored by the electrode. From points in the precentralis behind this area 

 it had been ascertained in' laryngoscopic examination that faradisation 

 evoked regularly adduction of the vocal cords; the topography of those 

 points is recorded in the map (tig. 27). From the tield explored forward of 

 the precentralis, however, no movement of vocal cords, larynx, lips, or 



I cm 



Fig. 27. — Map of the left hemisphere of cliimpanzee 14 ; a number 

 of the resj)onses obtained to faradisation both at the time of the 

 ablation-operation and at the subsequent final exploration are 

 mapped. The shaded area limited by sulci and dotted lines shows 

 the ablated area of the cortex. Ablation-experiment 7. 



tonorue was elicited. The larger portion of this latter field was then 

 ablated to a depth of about a centimetre and for the area enclosed by 

 the dotted line in fig. 27. There was little hsemorrhage. The dura was 

 stitched together, and the skin wound closed. Aseptic precautions had 

 been adopted throughout the operation. 



On recovering from the operation narcosis the animal showed no facial 

 or other paresis, and no impairment of its vocalisation was detected. It 

 was excited somewhat after coming round from the anaesthetic, and uttered 

 a variety of vocal sounds. The pitch of its voice was thought to be rather 

 higher than had been usual, but this may have been an after-result from 

 the inhalation of the anaesthetic, and was not observable later in the after- 

 noon nor subsequently. 



Next day : " animal seems irritable ; he screams, and is more noisy than 



