220 Leyton and Sherrington 



response just previously given from centralis anterior, and soon dies out 

 under repetition of the stimulus to gyrus centralis posterior, unless stimula- 

 tion of gyrus centralis anterior is repeated to renew it. 



12. Stimulation of the middle and posterior parts of the inferior frontal 

 convolution of left hemisphere failed in chimpanzee, orang, or gorilla to 

 evoke any vocalisation. Ablation of a large portion of that area in one 

 chimpanzee, chosen because it was a noisy and vociferous animal, produced 

 no obvious impairment or change in vocalisation. 



13. Faradisation of the surface of the insula failed, to evoke any 

 detectable results. 



14. Unipolar faradisation of the cut cross-face of the crusta (orang) 

 evoked responses separately in toes and ankle, hip, trunk, arm, and face 

 from a series of points taken in order from without inward (mesially). 

 From the cut cross-face of the pyramidal bundles in the pons (gorilla), 

 unipolar faradisation evoked toe movement predominantly from the most 

 lateral, face-tongue movement predominantly from the most mesial, and 

 finger movements predominantly from the intermediate. 



-^15. Ablation of the cortex of the larger portion of an arm or leg area 

 in gyrus centralis anterior produced heavy paresis of the corresponding 

 limb, but this paresis quickly lessened, and the limb soon regained in large 

 measure its volitional motility, and became successfully used for climbing, 

 picking up food, picking the teeth, etc. Ablation further of the greater part 

 of the arm area of the second hemisphere, after previous ablation of the 

 greater part of that area from the other hemisphere, induced no recrude- 

 scence of paresis in the already paretic and partly recovered arm. After 

 the double lesion considerable recovery of the volitional use of both limbs 

 somewhat rapidly ensued, the hands, for instance, being used freely in 

 climbing, picking up food, etc. 



16. The degenerations in the spinal cord following on limb-area lesions 

 exhibited a large crossed pyramidal tract, extending more to the edge of the 

 lateral column than in man, and in this respect resembling a feature seen in 

 the macaque cord. There was obvious also a slight ipsilateral pyramidal 

 tract in the ipsilateral lateral column, derived from a small portion of the 

 fibres of the pyramid passing not to the lateral column of the crossed side, 

 but to that of the ipsilateral side. There was also evident in two of the chim- 

 panzees an ipsilateral ventral pyramidal tract similar in position and relative 

 size to that ("direct Py. T.") commonly seen in man ; this is not existent in 

 the macaque. The pyramidal-tract degeneration after the arm-area lesions 

 descended beyond the brachial enlargement of the cord, but did not reach 

 the lumbo-sacral enlargement. The pyramidal-tract degeneration ensuing 

 on the leg-area lesions descended the whole length of the cord. Many fine 

 degenerate fibres (collaterals) were visible in the ventral horn of grey 

 matter among the motor perikarya on the side contralateral to the cortical 

 lesion in the brachial segments of the arm-area lesion and in the lumbo- 

 sacral enlargement in the leg^-area lesion. 



