52 The Enceplialon 



in eating or talking, for instance, confine the movements to one side 

 of the face. When, therefore, these centres are damaged on the one 

 hemisphere there is still some energy passing out to the opposite side 

 of the tongue, so that, as Ferrier remarks, we then find oro-lingual hemi- 

 paresis (napeo-is, relaxation) instead of paralysis. When the lesion is 

 in the left hemisphere the paresis of the right side of the tongue is 

 generally associated with aphasia, because, the lesion being in Broca's 

 region (p. 49), the centres for the muscles of speech tongue, lips, palate, 

 and vocal cords are also damaged. 



Sometimes, as already remarked, the oro-facial paresis is associated 

 with brachial paralysis. The association of left hemiplegia with 

 aphasia may happen in the case of a left-handed man, that is to say, in 

 one whose right cerebral hemisphere has acquired the habit of perform- 

 ing the offices usually, by preference, carried out by the left. 



It will simplify the problem of localisation if the student remembers 

 that the motor areas are inverted on the surface of the liemisphere 

 like the landscape on the plate of the photographic camera. Thus the 

 centres for the muscles of the lower extremity are grouped about the 

 top of the fissure of Rolando, the arm-centres about the middle, and 

 the centres for the face and mouth, and for the muscles of speech, at 

 the bottom near to the island of Reil. Thus it comes about in in- 

 complete hemiplegias that the leg and arm may be affected together 

 the face escaping ; that in another case the arm and face may be 

 affected without the leg ; and that aphasia is much more likely to occur 

 with paralysis of the right arm than of the right leg only, for the arm- 

 centres intervene between those of the muscles of articulate speech 

 and of the leg. (See illustration on p. 48.) 



On the mesial surface of the hemisphere \S\htgyrusformcatU* 

 (or arched convolution), which begins near the anterior perforated spot 

 and arches round the corpus callosum to become continuous with 



