The Excitable Cortex of the Chimpiinzee, Oranf;-rtan. and Ciorilla 197 



area yielding ankle movement and toes movement. Uyrus centralis 

 posterior was faiadised at points over the whole of its exposed surface, and 

 yielded no movements. The leg area was hounded in front by an ascend- 

 ing limb of precentralis superior tissure, and aljove that by a small vertical 

 fissure lying farther forward. Large veins entering the superior longi- 

 tudinal sinus near the mesial border of hemisphere precluded satisfactory 

 examination of that actual l)order. An incision parallel with the mesial 

 border, and only a few millimetres from it, was made to a depth of about S mm. 

 along the whole antero-posterior extent of the leg area ; and another along 

 precentralis fissure, and from it to the anterior end of the mesial incision ; 

 and another along the centralis sulcus, meeting posterior end of the mesial 

 incision ; and tinally, a transverse incision across centralis anterior close 

 above the large vein at the genu superius. Beginning from the mesial 

 incision, the cortex of the whole area enclosed by these incisions was then 



Fig. '24. — Map showing the limits of an ablation in the leg area of 

 the left liemis])here of a chimpanzee, ablation-expeiiinent 4. The 

 numerals refer to the motor resj)onses obtained; vide "list of 

 motor responses," ])p. 148 seq. , supra. The double ruled line 

 indicates the position of the mesial border of the hemisphere. 



removed to a depth of about a centimetre, so as to include buried portions of 

 leg area cortex in the side fissures (fig. 24). A transverse strip of cortex next 

 below this lesion, which had previous to the ablation given hip movements, 

 evoked after the ablation no movements of hip or leg, but gave instead 

 brisk movements of the abdominal wall, as did the strip of cortex immedi- 

 ately below it, which had yielded them prior to the ablation. Centralis 

 posterior after the ablation was irresponsive, as it had been before. 



The dural flaps were brought together and stitched ; the skin was 

 closed, and the whole operation completed, as it had been prosecuted, under 

 full asepsis. 



On recovering from the operative narcosis the animal showed slight, but 

 distinct, paresis of the right leg ; the leg could not support the animal on 

 the vertical bars of the cage so well as did the left leg. On landing on 

 floor from descending the bars of the cage the right leg did not seem able 

 for a moment to support the weight of the body, but yielded under it, so 

 that animal lurched to that side, and once rolled over. The weakness 

 appeared chiefly in the right ankle. There was apparently clumsiness in 



