138 Ley toil and Sherrington 



repetition of the stimulus he did not feel sure that the movement then 

 obtained was the same as that seen previously. In some instances words of 

 description were entered down which were equivocal, thus "ankle flexion," 

 leaving it uncertain whether the movement was dorsal flexion or plantar 

 flexion. But these imperfections where occui-rino- have not been allowed 

 to exclude the observation from the list. 



The main object in view being to ' localise " the motor function of each 

 cortical point yielding motor responses, the stimuli applied were systematic-* 

 ally kept of weak strength and not far above threshold value, and each 

 stimulus was applied usually quite briefly, e.g. l"-2" or little more. The 

 sequences of movement are therefore short, our intention being to determine 

 chiefly the primary movement yielded by the cortical point. 



We had supposed at commencement of our experiments that the 

 identification of exactly corresponding points in the two hemispheres of an 

 individual and in the hemispheres of diflerent individuals could be much 

 more nearly possible than our experience has left us with the impression 

 that in fact it is. The dissimilarity of the convolutional pattern of the 

 hemispheres even in individuals of the same species (Troglodytes niger), 

 and the seemingly variable relation of analogous functional points to sulci 

 of corresponding name, makes it practically impossible to decide with 

 sufficient exactitude what point on the hemisphere of one individual is 

 identical with a given point upon another hemisphere. But in spite of 

 this inability to determine what point on one hemisphere is anatomically 

 identical with some particular point on another hemisphere, our series of 

 experiments as they proceeded, each resulting in a detailed localisation 

 map, showed us clearly that in very many cases, probably in most, the 

 corresponding anatomical points in diflerent individual hemispheres did 

 not, as examined by faradisation in the course of experiment, yield motor 

 responses so nearly similar as to be noted as the same movement in our 

 movement list. Of this many illustrations can be fomid if the maps with 

 number references furnished in this paper are turned to. The movements 

 so obtained were related movements, often or indeed usually closely related 

 movements, but not identical, not rarely movements of opposite sense, 

 although of the same part. And many instances may be found in the 

 maps where one and the same movement, as noted by the observer, was 

 obtained in one hemisphere from some point which was clearly not that 

 at which it was obtained in another heujisphere, either the opposite hemi- 

 sphere of the same individual or the hemisphere of the corresponding side 

 in another individual. Our experience is thus clearly in harmony with 

 that of Shepherd I. Franz (17) on the macaque. Summarishig the 

 observations described in section ii. of his paper, he writes: "The data 

 show in diff'erent animals," i.e. different individuals of the same species, 

 Macacus rhesus, "and in different hemispheres a variety of distribution 

 of the areas concerned with the movements of the individual segments of 

 the leg and arm." 



