CH. L ] 



THE SPEECH AND TACTILE AREAS 



733 



It will be noticed in the diagram (fig. 450) that there are two 

 regions of the brain from which eye movements can be elicited ; one 

 is in the frontal lobe, the other at the occipital pole. The frontal eye 

 area is the motor centre for conjugate movements of the two eyeballs, 

 and in the lower monkeys is continuous with the rest of the motor 

 area, but in the higher monkeys and man is separated from the 

 Eolandic area by a field of inexcitable cortex. The occipital region 

 from which eye movements can be obtained is the visuo-sensory 

 sphere (see p. 736). 



The next illustration is an outline map of the left cerebral hemi- 

 sphere in man. In it are indicated the various motor and sensory 

 areas, which are largely deduced from experiments on the higher 

 monkeys. 



VISUO- PSYCHIC SPHERE 



VISUO-SENSORY SPHERE 



FIG. 451. Left cerebral hemisphere, outer surface. The lobes and the principal sulci are indicated by 

 their initial letters ; A.E.M., anterior centre for eye movements ; B.C., Broca's convolution. 



One part of the motor area is peculiar to man, and that is : 

 The Speech Centre. This is surrounded in the diagram by a 

 dotted circle and marked B.C. There are other centres concerned in 

 speech, as we shall see when considering the question of association 

 fibres ; but this is the centre for the muscular actions concerned in 

 speech. The discovery of this centre was the earliest feat in the direc- 

 tion of cerebral localisation. It was discovered by a French physician 

 named Broca ; he noticed that patients who died after hsemorrhage 

 in the brain, but who previous to death exhibited a curious disorder 

 of speech called aphasia, were found, after death, to have the seat of 

 the hsemorrhage in this convolution. The convolution is generally 

 called Broca's convolution. Experiments on animals are useless in 

 discovering the centre for speech. Sherrington found in the higher 

 apes that faradisation of the Broca area does not evoke vocalisation. 



The most curious fact about the speech-centre is that it is uni- 

 lateral ; it is situated only on the left side of the brain, except in 

 left-handed people, where it is on the right. We are thus left- 

 brained so far as the finer movements of the hand-muscles are con- 



