438 



Messrs. V. Horsley and E. A. Schafer. [Mar. 20, 



strong as to involve the risk of its spreading to neighbouring parts. 

 The anaesthetic used has generally been ether, sometimes mixed with 

 chloroform ; in one case in which morphia had been employed the 

 results of stimulation were much interfered with by the drug. The 

 induction coil used is of the du Bois-Reymond pattern, with the Neef 

 interrupter ; and the Helmholtz side- wire is always introduced for the 

 purpose of equalising the effects of the make and break shocks. The 

 electrode wires are carefully guarded except at their points, which 

 project slightly on one side, and the electrodes are so constructed as 

 to pass between the falx and the mesial surface of the brain with as 

 little disturbance as possible. 



We have for the most part throughout all our experiments taken 

 care only to employ an excitation just sufficient to call forth the 

 activity of the part of the brain immediately under the electrodes. 

 The best physiological test of the strength of the interrupted current 

 consists in placing the electrodes on the tongue, and many of our 

 results have been got with a stimulus which is only just perceptible 

 when tested in that manner. Results so obtained are of the greatest 

 value for the purpose of localising the function of a part, because 

 under these circumstances there can be no question that the current 

 does not spread beyond a very small area ; and with such a minimal 

 stimulus applied for but a short time it is not unfrequently found that 

 but a single muscle, or at most two or three, generally in succession, are 

 called into action. But for thus exactly localising centres for indivi- 

 dual muscles a much larger number of experiments will be necessary 

 than we have up to the present been able to make ; we will, therefore, 

 reserve for a future communication, in which we hope to deal more 

 fully with this question, the few positive results of this kind that we 

 have obtained, and here only consider the more general movements 

 called forth by excitation of particular parts of the convolution. 



We have in this way explored the mesial surface of the hemisphere, 

 or rather the marginal convolution of that surface, for it soon appeared 

 evident that on other parts of the mesial surface positive results were 

 not to be expected from electrical excitation. We have ascertained 

 that the excitation of definite localised portions of this convolution 

 gives rise to the contraction of perfectly definite groups of muscles, 

 or in some cases of single muscles, producing more or less co-ordinated 

 movements of the trunk and limbs, in the same manner as has been 

 shown by Ferrier and others to be the case with excitation of localised 

 portions of the external surface of the hemisphere. 



We can best explain the extent of the excitable portion of the mar- 

 ginal gyrus by reference to certain easily recognisable furrows on the 

 external surface of the hemisphere. One of the most conspicuous of 

 these is the furrow of Rolando, which, as in man, terminates superiorly 

 near the margin of the hemisphere, a little in front of the posterior 



