FUNCTIONS OF THE CEREBRAL HEMISPHERES 493 



(Jacksonian epilepsy) with lesions of certain parts of the central 

 convolutions. On anatomical grounds Meynert considered that the 

 posterior portions of the hemispheres were probably more nearly 

 connected with sensation, and the anterior with the power of move- 

 ment ; but direct evidence of motor localisation was first brought by 

 Fritsch and Hitzig in 1870. These observers pointed out, in contradic- 

 tion of the then received idea, that the grey matter of the cortex was 

 excitable, and that it was possible to evoke co-ordinated movements of 

 the limbs on stimulating the front part of the hemispheres in dogs with 

 weak currents. The results of their experiments are shown in Fig. 223. 



A. 



B. 



FIG. 224. Tracings to show latent periods of movements obtained 



by stimulating : 



A, grey matter ; B, underlying white matter of cortex. Time- 

 marking == ^sec. (F. FRANCK.) 



These experiments were soon after repeated and confirmed by Ferrier, 

 who extended his observations to the monkey, and more lately by 

 Horsley, Schafer, Beevor, Sherrington, and others in the higher 

 apes and man. It was formerly a subject of dispute whether the 

 movements resulting from stimulation of the cortex were due to the 

 excitation of the grey matter or of the underlying white matter. The 

 following facts show that the seat of the excitation is in the grey 

 matter : 



(1) A smaller strength of current is required to excite the grey 

 matter than the underlying white matter, after removal of the grey 

 matter. 



(2) In animals poisoned by chloral the grey matter is inexcitable, 

 though movements can still be aroused on stimulating the white 



