Page:Proceedings of the Royal Society of London Vol 69.djvu/220

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We have been engaged for some time past on inquiry into the physiology of the cerebral cortex of the anthropoid apes. We are able to lay before the Society some new facts regarding the topo- graphical distribution of function in the anthropoid brain. Our experi- ments have been carried out on individuals representing the four, species Pitliecus satyrus (Orang), Troglodytes gorilla (Gorilla), Troglodytes niger (Chimpanzee), and Troglodytes calv-us (Chimpanzee). The speci- mens so far have included ten adult individuals. Of Troglodytes niger one individual used was only a few months old.

The method of excitation employed for the cortex has been unipolar faradisation, in the manner previously adoped by one of us in examining the cortex cerebri for ocular reactions. This method allows of finer localisation than that possible with the double-point electrodes ordinarily used. The inductorium (Kronecker's pattern and scale) has been Helmholtzed.

This area we find to include continuously the whole length of the precentral convolution. It also enters into the whole length of the sukus centmlis, with the usual exception of its extreme lower tip and its extreme upper tip.

In all the animals examined, we have found the " motor " area not to at any point extend behind sulcus centralis. Feeble reactions can occasionally, under certain circumstances, be provoked by strong faradisation behind the sulcus cent rail*, but these are equivocal, and appear under conditions that exclude their acceptance as equivalent to " motor-area " reactions.

On the mesial surface of the hemisphere the " motor " area has extended less far down than was expected. It has riot extended to the calloso-marginal fissure. Certain areas near that fissure have yielded us movements, e.g., of shoulder, body, wrist, and fingers ; but