This observation led to the
establishment of a most important fact in connection with speech, viz. that
right-handed people use their left cerebral hemisphere as the executive
portion of the brain in speech. Subsequently it was shown that when
left-handed people were paralysed on the left side by disease of the right
hemisphere, they lost their powers of speech. But the great majority of
people are born right-handed, consequently the right hand being especially
the instrument of the mind in the majority of people, the left hemisphere
is the leading hemisphere; and since probably specialisation of function of
the right hand (dexterity) has been so closely associated with that other
instrument of the mind, the vocal instrument of articulate speech, the two
have now become inseparable; for are not graphic signs and verbal signs
intimately interwoven in the development of language and human
intelligence?
What has determined the predominance of the left hemisphere in speech? I
can find no adequate anatomical explanation. There is no difference in
weight of the two hemispheres in normal brains. Moreover, I am unable to
subscribe to the opinion that there is any evidence to show that the left
hemisphere receives a larger supply of blood than the right.
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