CHAP, ii.] THE BRAIN. 1053 



symptoms, by loss or impairment of particular movements. In 

 most of such cases, the cortical lesion has been of such an extent 

 as to involve a number of special areas at the same time, and so to 

 lead to loss or impairment of movement over relatively considerable 

 regions of the body, such as the whole of one arm ; and in general 

 the teaching of these cases of disease, while confirming the 

 deductions from the monkey, and giving us some general idea of 

 the topography of the human motor cortical region, has at present 

 given us approximate results only. Figs. 131 and 132 shew in 

 broad diagrammatic manner the position and relative extent of 

 the motor areas for the leg, arm and face in man, as far as has 

 yet been ascertained. To assist the reader we give at the same 

 time diagrams Figs. 129, 130 illustrating the nomenclature of 

 the surface of the human brain. 



One area is of special and instructive interest. Speech is 

 an eminently 'skilled' movement. We have seen that in the 

 monkey the area for the mouth and tongue lies at the ventral end 

 of the central fissure or fissure of Rolando, ventral to the arm 

 area, and that the extreme ventral and front part of the motor 

 region just above the fissure of Sylvius supplies an area which 

 we marked as that of phonation (Fig. 126). In the monkey the 

 area of phonation is determined by experimental stimulation ; in 

 man, in a similar position, on the third or lowest frontal con- 

 volution, sometimes called Broca's convolution, ventral to and in 

 front of, and probably overlapping backwards the area which in 

 Fig. 131 is marked ' face ' and which includes the mouth and 

 tongue, clinical study has disclosed the existence of an area which 

 may be spoken of as the area of ' speech.' Lesions of the cortex 

 in this area cause a loss of or interference with speech, the 

 condition being known as aphasia ; to this we shall presently 

 return. In Fig. 131 this area is shewn in an approximate 

 manner. 



The movements of speech are essentially bilateral movements. 

 In the dog and monkey various bilateral movements may be 

 excited by stimulation of the appropriate area in either hemi- 

 sphere; and analogy would lead us to suppose that in man, the 

 movements of speech would be connected with the speech area 

 in both one and the other hemisphere. The results of lesions 

 however shew that it is in most cases especially the left hemi- 

 sphere which is connected with speech ; it is a lesion in the third 

 frontal convolution of the left hemisphere, often associated with 

 other lesions of the same hemisphere leading to paralysis of the 

 right side of the body and face, which causes aphasia, it being 

 only in exceptional cases that the condition results from a lesion 

 of the corresponding area of cortex on the right hemisphere. 



In man, then, clinical study corroborates the conclusions de- 

 duced from the experimental investigation of the dog and of the 

 monkey, but still leaves us in uncertainty as to the question what, 



