guage. Some months later the motor vocal speech centre begins to
functionate. The memories of the auditory word images which are stored
up in the auditory speech centre play a most important part in the
process of learning to speak. The child born deaf grows up mute. The
visual speech centre comes into activity when the child is taught to
read. Again, when he learns to write and thus begins to educate his
graphic centre, he is constantly calling upon his visual speech centre
for the visual images of the words he wishes to produce. From these
remarks it will be seen that there is a very intimate association
between the auditory speech centre and the motor vocal speech centre,
also between the visual speech centre and the graphic centre.

_Auditory Aphasia._--The auditory speech centre is situated in the
posterior part of the first and second temporo-sphenoidal convolutions
on the left side of the brain. Destruction of this centre causes
"auditory aphasia." Hearing is unimpaired but spoken language is quite
unintelligible. The subject of auditory aphasia may be compared to an
individual who is listening to a foreign language of which he does not
understand a word. Word deafness, a term often used as synonymous with
auditory aphasia, is misleading and should be abandoned. Auditory
aphasia commonly interferes with vocal expression, for the majority of
people when they speak do so by recalling the auditory memories of words
stored up in the auditory speech centre. _Amnesia verbalis_ is employed
to designate failure to call up in the memory the images of words which
are needed for purposes of vocal expression or silent thought.

_Visual Aphasia or Alexia._--The visual speech centre, which is located
in the left angular gyrus, is connected with the two centres for vision
which are situated one in either occipital lobe. Destruction of the
visual speech centre produces visual aphasia or alexia. Word blindness,
sometimes used as the equivalent of visual aphasia, is, like word
deafness, a misleading term. The individual is not blind, he sees the
words and letters perfectly, but they appear to him as unintelligible
cyphers. When the visual speech centre is destroyed, the memories of the
visual images of words are obliterated and interference with writing, a
consequence of _amnesia verbalis_, results. On the other hand, when the
lesion is situated deeply in the occipital lobe, and does not implicate
the cortex, but merely cuts off t