The Excitable Cortex of the Chimpaiu.ee, Orang-Utan, and Gorilla 219 



macaque, permanent individual differentia existing from hemisphere to 

 hemisphere. 



(i. The motor responses obtained by faradisation from a baby chimpanzee 

 ei|ualled in ditierentiation, as far as could be seen, the average of tiiose 

 obtained from the adult of any of the three anthropoid species examined. 

 And '■ epilepsy " was produced neither more nor less easily than in those. 



7. The anterior edge of the motor area seems to fade away somewhat 

 gradually into inexcitable cortex. Farther forward still is a large diffuse 

 field, from scattered points of which, in the middle and inferior frontal 

 convolutions not extending to their more anterior parts, conjugate devia- 

 tions of the eyeballs and opening of both eyes are elicitable. But stronger 

 faradisation is recjuired for these, nor are the results so regular as with the 

 responses of the motor area proper. 



8. Eyeball movements similar to those just mentioned are likewise 

 obtainable from the occipital pole and from the calcarine region. 



9. The motor area for face and tongue movements seems, relatively to 

 the rest of the motor area, more extensive in orang than in chimpanzee. 

 Apart from that distinction, there seemed no clear difierence between the 

 motor area from species to species of the anthropoids examined. The 

 largest and most highly developed brain we examined was that of a gorilla, 

 and the motor area in that specimen appeared to be, on the whole, the 

 most extensive and differentiated of those experimented upon. 



10. The motor cortex may be regarded as a synthetic organ for 

 compounding and re-compounding in varied ways movements of varied 

 kinds of scope from comparatively small, though in themselves well 

 co-ordinate, fractional movements. For this synthesis the motor cortex is 

 provided with, i.e. has at call, these partial or fractional movements and 

 postures. The cortex obtains these partial movements, perhaps by analytic 

 powers of its own, from the bulbo-spinal mechanisms, but the higher of the 

 synthetic results of the bulbo-spinal mechanism exhibit, as judged from cat 

 and dog, certain only of the kinds of compound movements which the 

 motor cortex gives. From the recomposition of these partial movements 

 into wholes of varied pattern and sequence there result motor acts which, 

 taken in their entirety, making use of the same fractional pieces, attain 

 with them aims of varied scope by varying the spatial and temporal 

 combinations of them. 



11. The free surface of gyrus centralis posterior was found to difi'er 

 from that of gyrus centi-alis anterior in not being similarly excitable by 

 faradisation. Faradisation behind the sulcus centralis can, under certain 

 circumstances, evoke reactions from the cortex, but these are doubtful 

 for acceptance as equivalent to " motor-area " reactions. They appear as 

 'echo-responses" when the faradisation is made to follow directly and 

 quickly on faradisation of gyrus centralis anterior in the near neighbour- 

 hood, i.e. about the same horizontal level and not far from sulcus centralis. 

 The " echo-response " thus obtained from gyrus centralis posterior repeats a 



