626 



PHYSIOLOGY 



CHAP. 



handed make of the left brain, and the left-handed of the right 

 brain, during the years of education, in learning to speak, read, 

 write, and in performing finer and more skilled work. It is there- 

 fore reasonable, and well-confirmed by clinical evidence, that 

 lesions of the normal speech centres may be functionally com- 

 pensated by the symmetrical area of the opposite side. This 

 functional compensation or substitution is effected more readily 

 and completely in children than in adults. Gowers and 

 Mingazzini sustain that in the state of infancy the central speech 

 mechanisms are bilateral or at least more equally distributed 



FIG. 308. Area for speech and its three centres for verbal images. (Dejerine.) A, Wernicke's 

 centre, for auditory verbal images ; B, Broca's centre, for motor verbal images ; PC, centre for 

 visual verbal images. 



between the two hemispheres than in adults. But in adults, too, 

 according to the consensus of clinical evidence, there must be 

 considerable difference in individuals ; Gowers, Brans, and Collier 

 state that in right-handed people the left hemisphere has no 

 monopoly in speech. Hughlings Jackson, Bastian, and Byrom 

 Bramwell, also on the strength of clinical observations, have 

 assigned the function of premeditated speech to the left hemi- 

 sphere and the simpler function of automatic speech to the right 

 hemisphere. 



Severe lesions of Broca's convolution cause aphasia, that is 

 loss of the power of speech, owing not to paralysis of the nerves 

 and muscles thrown into action during phonation, but to abolition 

 of the memory of a certain order of co-ordinated movements 

 necessary to the articulation of words. The intelligence of the 



