x THE FOEE-BEAIN 625 



characterised by predominating development of the parietal and 

 occipital lobes. 



XV. To form a more adequate idea of the complexity of the 

 intellectual processes, we may briefly examine the most typical 

 forms of disturbance of speech. 



In a wide sense speech or language covers the sum of 

 all the means which man employs to express his thoughts. 

 Language is mimetic, phonetic, graphic (see Chap. III.), according 

 to the nature of the signs employed gestures, words, writing. 



Apart from mimetic language (which is the means of com- 

 munication for deaf-mutes, phonetic and graphic language have a 

 historical development in the race as in the individual. Com- 

 parative philologists endeavour to reconstruct the phylogenesis of 

 language ; psycho-physiological observations of the manner in 

 which the child learns gradually to speak, read, and write, reveal 

 the mode of development of language in the individual. Poverty 

 of language indicates poverty of ideas in primitive peoples as in 

 children ; wealth of language is the gauge of civilisation for the 

 most advanced nations, as for the most gifted and most highly 

 developed minds. 



The spoken or written word is the symbolical representation of 

 the idea, which is necessary in order to express it, or communicate 

 it to others. The highest organs of ideation, while intimately 

 connected with, are entirely distinct and separate from, the organs 

 of speech. In fact, serious mental disturbance may coexist with 

 perfect integrity of phonetic and graphic speech. On the other 

 hand, psychological analysis and clinical observations show that 

 the mechanism by which ideas are clothed in verbal symbols is 

 very complex, and involves the intervention of three associated 

 centres : the centre for the motor images of words ; the centre for 

 phonetic verbal images ; the centre for visual verbal images. The 

 first (Fig. 308) is Broca's centre, which occupies the foot of the 

 left third frontal convolution; the second is Wernicke's centre 

 seated in the left first temporal convolution and supramarginal 

 gyrus ; the third lies in the occipito-parietal lobe near the visual 

 area according to Dejerine it is placed in the left angular gyrus. 



These three centres together form an area peculiar to the 

 human brain, the so-called speech centre, comparable to the 

 sensory-motor, visual, auditory and other areas which we have 

 been discussing. But unlike these the speech centre is single or 

 unilateral ; it lies in the left hemisphere in right-handed people, 

 in the right hemisphere in the left-handed. This asymmetrical 

 unilateral development of the central organs of speech is purely 

 functional and not morphological, for the right hemisphere presents 

 the same structure and connections as the left. The different 

 functional importance of the two hemispheres in speech evidently 

 depends on the larger and almost exclusive use which the right- 



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