MINUTE ANALYSIS OF CORTICAL CENTRES. 
1G1 
We would first draw attention (see fig. 5) to the fact that the movement of simple 
extension is alone represented in the posterior extremity of the middle frontal 
convolution (according to our view), viz., at centres 12, 13, 12', and 13' (see Table 3 
and fig. 5). It will be observed, on Table 3 that in three instances we noted 
interosseal flexion in this region. Discussion of the relation between interosseal 
flexion and extension of the digits we shall enter into further on. 
As regards the movement of flexion, we find that it is represented over the whole 
of the area which has been the subject of our investigations, with the exception of 
the centres above mentioned, viz., 12, 13, 12', and 13'. We have now to draw 
attention to some extremely important considerations concerning the relative repre¬ 
sentation of the movements of flexion and extension. We have just seen that pure 
extension was limited to certain centres ; we have now to add that we have only seen 
pure flexion at centres 1, 1', 4, and 4'. We are not inclined to lay much stress on 
this limitation of the representation of the movements of pure flexion and extension, 
but we note the foregoing facts for the purpose of recording them. 
We will now consider what appears to us the much more important co-operation of 
these two movements of flexion and extension of the digits. On this point we have 
obtained the exceedingly definite result that both movements are represented in the 
middle ^ of the ascending frontal and parietal convolutions, and that, while in the 
ascending frontal convolution extension precedes flexion, in the ascending parietal 
convolution this order is reversed, and so extension follows flexion. In view of the 
fact that pure extension is only represented in 12, 12', 13, and 13', i.e., in those 
centres which are immediately in front of the middle ■§- of the ascending frontal 
convolution, we readily understand how it comes about that in the ascending frontal 
extension 'precedes flexion, whereas behind the fissure of Rolando it follows flexion. 
We have observed interosseal flexion to precede long flexion in three cases, and only 
in the centres 8', 2, 2', 12, and 3. It is obviously possible that this interosseal flexion 
of the digits, consisting of flexion of the metacarpo-phalangeal joints and extension 
of the phalangeal joints, should co-exist in perfect harmony with long extension of the 
digits. It must not be understood that in all the remaining cases interosseal exten¬ 
sion of the phalanges leads the way for the action of the long extensors; indeed, in 
many instances it appeared to us that preliminary extension of the digits was so 
sharp and complete as to be explained only by rapid and perfect action of the long 
muscles. TVe must add, however, that, although this preliminary extension of the 
fingers was extremely well marked, it was of very brief duration, whereas the 
subsequent flexion was very powerful, and was maintained as long as the electrodes 
were applied to the cortex. 
Although we have thus written at some length on the relation between flexion and 
extension of the digits, we do not consider that the results were sufficiently absolute 
to permit of our speaking dogmatically, and we hope that further research will 
ultimately solve this problem. 
MDCCCLXXXVir.-B. Y 
