158 
DIE C. E. BKEY'OR AND PROFESSOR Y. HORSLEY ON A 
Since in all the brains we have experimented upon the positions of the principal 
sulci were perfectly constant, we regarded them as definite landmarks by which we 
could accurately ascertain in different brains the position of each centre. 
Thus, commencing above in the ascending frontal convolution, we took as our first 
landmark the sulcus x, and in the horizontal line behind it we placed our two first 
centres, 1 and 1' (these to be explained directly, see fig. 1), and then placed opposite 
the level of the upper end of the prsecentral sulcus the centres 3, 3'. Dividing the 
interval between these points (which in the average brain of the animals we employed, 
i.e., nine out of the ten experiments, was 1 cm. in length) into two equal parts, we 
designated the point of division by the ciphers 2 and 2'. Below 3 and 3' we placed 
4, 4' and 5, 5' at distances equal to that between 2, 2' and 3, 3'. 
(The distance between the electrodes was 2 millimetres, and they were applied 
parallel to the longitudinal fissure at the points designated by the figures described 
above. These points or centres were about 4 mm. apart. Thus a considerable 
interval was left between the centres, which we explored in the same way, but we 
have not deemed it necessary to give the results of exciting the cortex at these 
intervals, since in every case they simply corroborated the effects obtained by stimu¬ 
lating the parts bounding them.) 
We further found that the ascending frontal and middle-frontal gyri were so broad 
as to necessitate a vertical subdivision. To meet this contingency, we employ the 
plain figures for the centres of the posterior half, and figures dashed thus, 1', for the 
anterior half; both, of course, being on the same horizontal level. 
On reference to Table 3 it will be seen that, with the exception of the fingers and 
thumb, the absolute number of times that any movement is produced is much less in 
the ascending parietal than the ascending frontal convolutions, and further that the 
representation of even the thumb and index decreases as the gyrus is explored from 
below upwards. 
From our experiments it appears to us that the ascending parietal convolution has 
less claim than the ascending frontal to be considered as an area of extensive represen¬ 
tation of movement. We have been so impressed with the importance of deciding this 
fact that we have usually explored the former gyrus with the current directly after the 
skull has been removed, and subsequently repeated our examination of it at various 
intervals during the experiment, so as to eliminate any error in the direction of loss of 
excitability of the cortex of this gyrus. 
We would call attention to the extraordinary degree of symmetry which exists in 
all the Monkeys on which we have experimented, and also that this is not merely 
morphological, but also physiological. Although this is a matter of great interest, we 
cannot enter into it in further detail. 
Before giving the detailed results of our work, we would lay down the following 
axioms founded on our experiments. 
Axiom 1.—Viewing as a whole the “motor area’ of the cerebral cortex for the 
