FUNCTIONS OF THE CEREBRAL HEMISPHERES 455 



There are, however, considerable difficulties in the acceptation of this 

 traditional classification. Microscopic examination of Broca's convolution 

 shows a type of cortex entirely different from that part, viz. the psycho- 

 motor area of the ascending frontal convolution, which is concerned with 

 the higher cerebral processes resulting in movement. Its structure is in fact 

 identical with that described by Campbell as the ' intermediate precentral 

 area ' and regarded as characteristic of the association areas. Moreover it is 

 difficult to comprehend how a function such as speech, with its enormously 

 complex mechanism, could be limited to so small a portion of the brain as 

 Broca's convolution. The neural basis of language must in fact be co- 

 extensive with the sensory centres (the projection spheres) and with the 

 whole region of lower association. We might indeed speak of auditory and 

 visual word- centres as located in the visuo-psychical and auditory psychical 

 centres. There is probably, however, no word, still less a collection of words, 

 expressing an idea, which does not involve the activity of practically all parts 

 of the cerebral cortex. As Bolton * points out, " a word, such as ' mouse,' at 

 once sets in effect processes of association which pass to every projection 

 sphere with the solitary exception of the gustatory, and even this may be 

 aroused in a person who has eaten a fried mouse in the hope of thereby 

 recovering from an attack of whooping-cough." 



A careful examination of an extensive series of cases by Marie has shown, 

 in fact, that Broca's aphasia does not exist as a result of lesions of Broca's 

 convolution. This part of the brain may be destroyed without any disorder 

 of speech. The cases described by Broca of motor aphasia are really cases of 

 sensory aphasia from lesion of Wernicke's area, combined with anarthria due 

 to subcortical injury of the fibres of the internal capsule. The statement 

 that there is no loss of intelligence in these cases of so-called motor aphasia 

 does not bear investigation. Although as patients they may comport 

 themselves reasonably, as soon as they have to perform any duties which 

 have been learnt by them in connection with their ordinary avocations 

 they show their deficiency. They are incapable of transacting ordinary busi- 

 ness, at any rate to the extent to which they were before the lesion. The 

 amount of impairment of intelligence will vary in different cases according 

 to the extent of the lesion. Thus softening generally affecting the occipital 

 lobe may, with hemianopia, cause ' word-blindness,' or alexia, a loss of power 

 of appreciating the meaning of pronounced or written words. In most 

 individuals, and certainly in the uneducated, this power may be cut out 

 altogether without interfering considerably with the mental powers. On 

 the other hand, from babyhood upwards we have learnt the meaning of words 

 and their grouping by auditory impressions. If the whole of the auditory 

 associations be destroyed by an extensive lesion in the first and second tem- 

 poral convolutions the resulting loss of word appreciation, sensory aphasia, 

 will be attended with great diminution of mental powers. It must be 

 remembered that the area of Wernicke is not a sensory centre, but a centre 

 of association between the various sense-impressions, especially those of 

 * In his admirable article in Hill's " Further Advances in Physiology." 



