The Excitable Cortex of the Chimpanzee, Orang-Utan, and Gorilla 211 



systematically examined by the electrodes, revealed nothing abnormal in 

 its resj)onses, either in the direction of excessive or of defective response. 

 The animal was then destroyed by chloroform. 



In another experiment (tig. 2S) the lower part of the gyrus was exjjosed, 

 and after point-to-point examination of it with the electrodes had been 

 found to yield no motor or other detected responses the gyrus was ablated 

 with the knife from close above inferior cjenu downward for one-half of its 

 length below that genu. The anterior boundary of the ablation was made 

 by thrusting the knife between the lips of that part of sulcus centralis and 

 sloping it downward and backward through the posterior wall of the fissure 



.Cf- 



Fio. 28. — Lesion in gyrus centralis posterior giving no symptoms and no degeneration in bulb 

 or spinal cord ; chimpanzee, ablation-experiment 10. 



thus avoiding the floor of the sulcus and the deepest portion of the posterior 

 wall. The width of the ablated portion in its upper part extended back to 

 the lower spur of the post-central sulcus, and below that parallel with sulcus 

 centralis and 15 mm. behind it. The lowest boundary ran horizontally from 

 sulcus centralis to the posterior cut behind. 



On recovering from the anaesthetic the animal showed no trace of 

 paresis either in hand or face, no impairment in mastication or drinking 

 or swallowing, in short, no detected departure from normal motility. The 

 skin of the right half of the face could feel, but it was not possible to 

 assure oneself that its sensation was undisturbed and actually normal. 

 Fifteen days later the animal was used for systematic examination of the 

 motor cortex, and the precentral gyrus throughout its facial as well as its 



