208 On the Cerebral Cortex of some of the Higher Apes. 



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. 



III. Other Regions of Cortex. 



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. 



DESCRIPTION O1T PLATE 4. 



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 pre- 

 central sulcus. 



