OBSERVATIONS ON IHE HXCITABLh: C(JKTEX OF THE 

 CHIMPANZEE. ORANG-UTAN. AND GORILLA. By A. S. F. 

 Levton and C. S. ShekriX(;ton. ( With thirty figures in the text.) 



(Reoiived for publication (Jrtoher 4, 19IH.) 



CONTENTS. 



I. Introddction, and Mkthods Employed ..... "^^35 

 II. Experiments by Stlmclation • . . . . 137 



1. Prefatory remarks ou " localisatiou" of point.< in the motor cortex ; 



functional instability of the motor points a>^ evidenced bv facilita- 

 tion, reversal, and deviation of response " . 137 



2. List of motor responses observed, and the topography of their cortical 



points ; " buried " portion of the motor cortex : remarks on the group- 

 ing of the cortical motor points ; inferences as regards the functions 

 of the motor cortex . . . . . . .144 



III. E.XPERIMENTS BY ABLATION ....... 180 



Protocols of experiments and degenerations of the pyramidal tracts 



observed . . . ". .180 



Remarks on the ablation experiments ..... :>06 



IV. Experiments on Gyrus centralis posterior .... 208 



V. Stimulation of Surface of Insula . . . . .212 



VI. Cortical Thre.^hold to Faradisation in Arm Area of C.\t. Macaque, 



AND Chimpanzee compared . . . . . .212 



VII. Influence of Local Cold and Warmth applied to Scalp on Tempera- 

 ture OF Cortex (Chimpanzee) . . . . . i>i4 



^ III. Closure of Carotid Arteries and Excitability of Cortex 



(Chimpanzee) . . . . . . . .215 



IX. L.JCALISATION OF FiBRES OF THE PYRAMIDAL TRACT IN CrUSTA (OraNG) 



and in Pons (Gorilla) ....... 216 



X. Summary of Conclu.sions ....... 2I8 



References . . . . . ogi 



L IXTRODUCTIOX. 



The inve.stigation the results of which are liere recorded arose from an 

 observation, which chance opportunity afforded us. of examining by stimu- 

 lation the cerebral cortex of a chimpanzee. That anthi'opoid species had 

 not at that time come under experimental examination. On faradising the 

 cortex we found, contrary to our expectation, that, although the gyrus 

 centralis anterior yielded motor responses readily, we obtained none such 

 from gyrus centralis posterior. A second similar opportunity arising, we 

 repeated our experimental tests, and the results contirmed our former ones. 

 Obtaining then a .specimen of gorilla, an anthropoid also not previously 

 experimented on, results were again met confirmatory of our tirst. It was 



