The Excitable Cortex of the Ciiiinpanzee, Orang-Utan, and Gorilla 207 



The paresis of the limb whose corresponding motor cortex area had 

 been heavily damaged by al^lation was severe, as evidenced by imperfection 

 of willed movements attempted to be executed by it in the early days 

 following upon the inllicting of the lesion. But this paresis was largely 

 temporary. Improvement in the willed actions of the limb set in very 

 early, and progressed until the limb was finally used with much success for 

 many purposes even of the finer kind. Thus after destruction of the 

 greater part of the arm areas of both hemispheres the two hands were 

 freely and successfully used for breaking open a banana and bringing the 

 exposed pulp of the fruit to the mouth. And again, after considerable 

 destruction of one leg area the foot was successfully used for holding on 

 the bars when climbing about the cage. As we said in our preliminary 

 communication, the absence of recrudescence of the hand paresis on ablating 

 the remaining intact part of the arm area showed that that latter part of 

 the cortex had not taken over the functions, at least not to any marked 

 extent, of the ablated portion. " In accord with the absence of recru- 

 descence of the hand paresis on ablating the remaining intact part of arm 

 area was the finding that faradisation of that part (elbow and shoulder) 

 provoked as usual movements of elbow and shoulder, but not of hand 

 itself, or only of hand late in a general arm movement, and that very 

 rarely. In short, neither the ablation or excitation methods gave any 

 evidence that the remaining part of the arm area had taken on the func- 

 tions of the ablated hand area. Neither was the gyrus centralis posterior 

 appreciably altered under exploration, and had not become a stimulable 

 area for arm, hand, or other movements." And recently it has been found 

 by T. Graham Brown and one of us, and by the former in independent 

 observations, that subsequent ablation of the adjoining centralis posterior 

 does not cause recrudescence of the arm paresis. Further, as pointed out 

 in our preliminary communication, the double arm area lesion showed 

 clearly that the regaining of ability to use the limb could not be attributed 

 to the arm area of one hemisphere taking over the functional powers of 

 the arm area of the other hemisphere after the latter's ablation. This 

 confirms for the anthropoid the result obtained in the dog by Francois 

 Franc k (15), and is itself confirmed by an experiment on the chimpanzee 

 published by T. Graham Brown and one of us (7) much more recently. 

 On the other hand, that in the movements of some parts the motor 

 cortex of one hemisphere is supported in its function by the correspond- 

 ing part of the motor cortex of the other hemisphere is indicated by our 

 ablation-experiment on the eye-closure area. In it the ablation of the 

 area from one hemisphere produced very little paresis of the movement, 

 but a rapidly successive ablation of the corresponding area from the other 

 hemisphere brought about distinct paresis. In this instance the movement 

 impaired tends usually to be a bilateral one : and that seems the main 

 factor accounting for the different result. 



The absence of obvious symptoms resulting from destruction of a large 



VOL. XL, NO. 2. — 1917. 14 



