Page:Proceedings of the Royal Society of London Vol 69.djvu/222

208 remarkably regained in the hand, so that it was once more used for climbing, &c. The animal ultimately not unfrequently fed itself with fruit, making use of that hand alone. Even small ablations in the precentral gyms have led to severe though quickly diminishing pareses. On the other hand, ablations of even large portions of post- central gyrus have not given any even transient paresis.

Our observations indicate that the frontal region, yielding conjugate deviation of the eyeballs, presents such marked differences of reaction from the "motor" area of the Rolandic region that we hesitate to include it with the so-called " motor " cortex ; it seems necessary to distinguish it in a physiological category separate from that. Spatially it is wholly separated from the Eolandic " motor " area by a field of " inexcitable " cortex.

As to the occipital lobe, only from the extreme posterior apex of the lobe and from its actual calcarine region has faradisation yielded any movement (eyes), and then not easily.

"VVc hope at no long distance of time to be able to lay before the Society a detailed account of the completed investigation. Some of our experiments are still in progress.

It is a pleasure to record here our indebtedness to Dr. L. Mond, F.E.S., for enabling us to bring these experiments to their present stage.

Brain of a Chimpanzee (Troglodytes niger). Left hemisphere viewed from side arid above so as to obtain as far as possible the configuration of the sulcus centralis area. The figure involves, nevertheless, considerable foreshortening about the top ar.d bottom of sulcus centralis. The extent of the "motor" area on the free surface of the hemisphere is indicated by the black stippling, which extends back to the sulcus centralis. Much of the "motor" area is hidden in eulci ; for instance, the area extends into the stile, centralis and the side, precentrales, also into occasional sulci which cross the precentral gyrus. The names printed large, in red, oa the stippled area indicate the main regions of the "motor" area; the names printed small, in red, outside the brain, indicate broadly by their pointing lines the relative topography of some of the chief sub-divisions of the main regions of the " motor " cortex. But there exists much overlapping of the areas and of their sub-divisions which the diagram does not attempt to indicate.

The shaded regions, marked " Eyes," indicate in the frontal and occipital regions respectively the portions of cortex which, under faradisation, yield conjugate move- ments of the eyeballs. But it is questionable whether these reactions sufficiently resemble those of the "motor" area to be included with them. They are therefore marked in vertical shading instead of stippling as is the " motor " area. S.F. = superior frontal sulcus. S.Pr. = superior precentral sulcus. I.Pr. = inferior precentral sulcus. and Slwr/ingfon.