CHAP. XXX.] HIGHER CEREBRAL FUNCTIONS. 681 



offered. It lias been thought that a certain more 

 forward condition of development of the left hemisphere 

 as a result of hereditary right-handedness recurring 

 through generation after generation might gradually 

 hecome sufficient to cause the left Hemisphere to ' take 

 the lead ' in the production of Speech-movements. Some 

 little evidence exists though at present it is very small 

 to show that it is left-handed people more especially 

 who may become Aphasic by a lesion of the right third 

 frontal gyrus. It is practically certain, indeed, that the 

 great preponderance of right-hand movements in ordinary 

 individuals must tend to produce a more complex organ- 

 ization of the left than of the right Hemisphere, and this 

 both in its sensory and its motor regions. We may con- 

 fidently look for the existence in it of the organic basis 

 of a vastly greater and more complex Tactile experience ; 

 and as movements of the right arm and hand are more 

 frequent, both as associated factors of this experience 

 and in other ways, we have also a right to expect that the 

 Kinsesthetic Centres will be similarly developed to a 

 notably greater degree in the left Hemisphere. And as a 

 matter of course also the nervous mechanisms for the 

 movements with which these sensory impressions are 

 associated would be much more complex in the Motor 

 Ganglion of the left than in that of the right Hemisphere. 

 Many years ago, moreover, the writer ascertained a fact 

 which at the time seemed very difficult to understand 

 viz., that the specific gravity of the cortical Grey Matter 

 of the Brain in left frontal, parietal, and occipital regions 

 is often distinctly, though slightly, higher than that from 

 corresponding regions of the right Hemisphere.* But 

 such an increase in specific gravity might be produced by 



* See a paper " On the Specific Gravity of the Human Brain," 

 in " Jrnl. of Mental Science," 1866, pp. 28, 32. 



