y mind, solved by the fact that in the long procession of ages
evolution has determined right-handed specialisation as being more
advantageous to the progress of mankind than ambidexterity.
Right-handedness is an inherited character in the same sense as the
potential power of speech.

LOCALISATION OF SPEECH CENTRES IN THE BRAIN

In 1863 Broca showed the importance in all right-handed people (that is in
about ninety-five per cent of all human beings) of the third _left_ frontal
convolution for speech (_vide_ figs. 16 and 17); when this is destroyed by
disease, although the patient can understand what is said and can
understand written and printed language, the power of articulate speech is
lost. _Motor Aphasia_. This portion of the brain is concerned with the
revival of the motor images, and has been termed by Dr. Bastian "the
glosso-kinaesthetic centre," or the cortical grey matter, in which the
images of the sense of movement of the lips and tongue are formed (_vide_
fig. 17). A destruction of a similar portion of the cortex in a
right-handed person produces no loss of speech; but if the person is
left-handed there is aphasia, because he, being left-handed, uses the third
_right_ inferior frontal convolution for speech. These facts have for long
been accepted by most neurologists, but recently doubts have been cast upon
this fundamental principle of cerebral localisation by a most distinguished
French neurologist, M. Marie; he has pointed out that a destructive lesion
of the cortex may be accompanied by subcortical damage, which interrupts
fibres coming from other parts of the brain connected with speech.

In the study of speech defects it is useful to employ a diagram; a certain
part of the brain corresponds to the _Speech Zone_ there indicated, and
lesions injuring any part of this area in the left hemisphere cause speech
defects (_vide_ fig. 17). All neurologists, M. Marie included, admit this,
and the whole question therefore is: Is a destruction of certain limited
regions of the superficial grey matter the cause of different forms of
speech defects, or are they not due more to the destruction of subcortical
systems of fibres, which lie beneath this cortical speech zone?

There is a certain portion of the speech zone which is assumed to be
connected with the revival of written or printed language, and is called
the _visual word-centre_. There is another region connected with the memory
of spoken words--th