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Motor Localisation in the Brain of the Gibbon, correlated with a 

 Histological Examination* 

 By F. W. Mott, Edgar Schuster, and C. S. Sherrington. 



(Communicated by Prof. C. S. Sherrington, F.R.S. Received March 28, — 

 Read May 4, 1911.) 



Motor localisation in the Gibbon has not been hitherto determined 

 experimentally, probably owing to the difficulty of obtaining a suitable 

 animal. It appeared to be desirable, therefore, to see whether the habits 

 and mode of life of this animal could be correlated with an increased 

 development of the motor cortex. One of us (F. W. M.) had some years ago, 

 by a comparative study of the convolutional pattern of the brains of Lemurs 

 and Apes, made the following deduction :f " The remarkable use this animal 

 makes of its arms and hands can be correlated with a remarkable expansion 

 of the cortex in the precentral region, as shown by the development of 

 a broad gyrus extending from the middle of the precentral region to form the 

 second frontal convolution. Now if we turn to the Ape's brain (Macacus), 

 and see what the effect of this development would be, we observe that it 

 would push forwards and downwards that portion of the cortex which on 

 stimulation gives rise to movement of the head and eyes, particularly that 

 which gives rise to eye movements, etc." Figures were shown to indicate 

 that the sulcus arcuatus would be pushed down to join the sulcus rectus. 

 The following experiments by stimulation, correlated with a complete 

 histological examination of the cortex in front of the central sulcus, have 

 confirmed this deduction. 



The animal used for the experiments was a male and black in colour ; it 

 was remarkably agile ; when standing or running on the ground it main- 

 tained almost an erect posture, using its long arms to balance itself very 

 much as a man would walk on a tight rope with a balancing-pole. It was 

 kept for some days before the experiment in the animal room of the 

 Physiological Laboratory, Liverpool, and it was frequently heard to utter 

 vocal sounds of very varying pitch and quality. Thus it could imitate the 

 shrill high-pitched whistles of the guinea-pig and the relatively low-pitched 

 bark of the dog. A short account of the larynx of this animal will be made 

 the subject of a future publication. 



* A portion of the expense of this research has been defrayed by a Government Grant 

 from the Royal Society. 



t "On the Physiological Significance of the Convolutional Pattern in the Primates,"' 

 ' Brit. Med. Journ./ 1906. 



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