676 THE BRAIN. 



attacks of which we are speaking, it has been inferred that the immediate 

 exciting cause of the attack is to be sought in events taking place in that 

 part of the cortex which serves as the area for the movement which ushers 

 in the attack. Further inquiry has not only confirmed this view, but has 

 also shown that the topography of the cortical areas in man, as thus deter- 

 mined, very closely follows that of the monkey. 



Other diseases of the cortex have been marked, among other 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. 154 and 155 show 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. 152 and 153) illustrating the nomen- 

 clature 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. 149). In the monkey the area 

 of phonation is determined by experimental stimulation ; in man, in a 

 similar position, on the third or lowest frontal convolution, sometimes called 

 Broca's convolution, ventral to and in front of, and probably overlapping 

 backward, the area which in Fig. 154 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. 154 this area 

 is shown 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 hemisphere ; 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, show that it is in most cases especially the left hemisphere 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 hemi- 

 sphere 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 deduced from 

 the experimental investigation of the dog and of the monkey, but still leaves 

 us in uncertainty as to the question what and what alone are the absolutely 

 permanent effects of the loss of a cortical area and nothing else. On the 

 one hand, in the cases in which recovery of a movement follows upon its 

 loss or impairment, it is open for us to suppose that the lesion itself was tem- 

 porary, and that with the cure of the malady the cortical area regained its 

 normal condition. On the other hand, where the disease continues, the per- 

 manency of the loss of any movement may be attributed to the disease 

 doing more than merely suspend' the function of the cortical area. Aphasia, 



