174 Ley ton and Sherrington 



alone was, however, obtainable occasionally, and notably in two very young 

 chimpanzees. Isolated movement of annulus was never obtained. Closure 

 of the whole hand was usually easily obtained, but the degree of separate- 

 ness of the representation of the fingers as a group from that of thumb 

 was marked. Over and over again all the fingers were extended or flexed 

 without accompanying movement of thumb. 



Wrist. The motor field for wrist is extensive, and both flexion 



and extension are readily elicitable, the foci for the two lying not 

 too-ether, although near one another. The responses of wrist are closely 

 bound up with those of fingers, but the former's focal field lies higher up 

 the convolution. Wrist responses sometimes were obtainable from points 

 very far forward, in front of precentral sulci, e.g. fig. 6, and then commonly 

 in association with index and thumb ; but there also the wrist tended to 

 have its representation higher upon the face of the hemisphere than either 

 thumb or index. There appears no great predominance in representation 

 of flexion over extension or extension over flexion in regard to wrist when 

 observations made in a number of hemispheres are taken together, although 

 in a single experiment on a single hemisphere one or the other ma}^ appear 

 to predominate. 



Elbow. — Elbow has a large focal field, situate higher up centralis 

 anterior than is wrist's, and below the shoulder's. Flexion of elbow 

 predominates over extension in its representation. The two focal fields 

 are commingled, but the smaller extension focus, in our experience, lies 

 posterior to that for flexion ; some of it lies buried in sulcus centralis. 



Shoulder. — These movements are, as was to be expected, represented in 

 a wide focal area, occupying their well-known position at the top of arm 

 area. Their area extends into both central and precentral sulci. Genu 

 superius varies much in prominence, and not rarely a small spur fissure, 

 generally cutting into centralis anterior from behind, but sometimes from 

 in front, lies partly, or rarely wholly, across the convolution at level of the 

 o-enu. Into the lower wall of this spur fissure shoulder area sometimes 

 dips. Shoulder area merges somewhat gradually into elbow area below 

 and into a chest-wall area above. 



4. Trunk Area. 



Chest Wall. — ^There is a small area focal for movements of the 

 contralateral chest wall. This lies opposite or close below genu superius 

 of sulcus centralis. It lies partly buried in anterior wall of that sulcus, 

 and in the spur fissure usually when tliat is present. It merges upward 

 quickly into an area focal for movements of the abdominal wall. 



Abdominal Wall. — Movements of the contralateral abdominal wall are 

 very regularly elicitable from a small area situate at the genu superius 

 level. The area merges in chest- wall area below and hip area above. The 

 movements are, in our experience, always unilateral and contralateral. 

 Some of the area commonly lies buried in sulcus centralis, and in the spur 



