734: FUNCTIONS OF THE CEREBRUM [CH. L. 



earned, as in writing, and we are also left-brained in regard to speech, 

 an action intimately associated with writing. There is but little 

 doubt that spoken language originated from gesture language; in 

 fact, one sees this in children learning to speak. In gestures the 

 right hand (and left brain) will take a prominent part; hence the 

 unilateral position of the speech centre receives a rational develop- 

 mental explanation. 



That Broca's area is the chief speech centre has for long been a matter of doubt 

 among physiologists and pathologists. The recent researches of Marie have thrown 

 further doubt upon the hypothesis ; for he has shown that in many cases of 

 aphasia Broca's area is uninjured, and that in cases where Broca's area is injured, 

 aphasia is not always present. His main conclusion is that injury to Broca's 

 convolution is only one factor in the causation of aphasia ; the other areas related 

 to the speech mechanism are situated more posteriorly, and are called the visual 

 word area and the auditory word area (see further, p. 741), and injury to these 

 alone will produce aphasia, whereas injury to Broca's area alone will not do so ; he 

 argues that the cases described in which aphasia followed an injury, apparently 

 limited to Broca's area, had not been thoroughly investigated, and if the other 

 areas had been properly examined injuries would have been found there also. 

 These conclusions will naturally be tested in the future by others who have the 

 opportunity of examining such cases. 



The Tactile Area. Volition and the tactile and muscular senses 

 are associated together so closely physiologically, that anatomically 

 we should expect to find the commencement of the volitional fibres 

 not far removed from the terminations of the sensory fibres, and as a 

 matter of fact, this is actually the case. Some of the sensory fibres 

 possibly pass direct into the ascending frontal convolution, but 

 the vast majority terminate in its neighbour the ascending parietal 

 convolution, which is on the other side of the central or Eolandic 

 fissure. In the early days of brain map-making, the ascending 

 parietal convolution was believed to be a part of the motor area, and 

 this found expression in such diagrams as those of Terrier (see fig. 

 449). A cortical injury in man seldom involves the ascending 

 frontal without also involving the ascending parietal, and so loss of 

 sensation and motion usually go together. The more exact methods 

 introduced by Sherrington and Griinbaum have, however, shown 

 that stimulation of the ascending parietal produces no direct move- 

 ments ; secondary movements may be elicited, just as stimulation of 

 the visuo-sensory area provokes secondary movements of the eyes. 

 Extirpation of the ascending parietal, however, leads to no motor 

 paralysis, and no degeneration of the pyramidal tracts. Histological 

 examination of the ascending parietal grey matter shows it, moreover, 

 to possess the structure of a sensory rather than of a motor area. 

 Before this distinction was recognised, the term sensori-motor was 

 used as a comprehensive expression to include the functions of the 

 two convolutions one on each side of the Eolandic fissure. The 

 ascending parietal convolution is the cortical seat of those sensations 



