ration: Fig. 16.--Side view of the left hemisphere, showing the
location of the "speech centers." The region marked "Motor" is the
motor speech center, that marked "Auditory" the auditory speech
center, and that marked "Visual" the visual speech center. (Figure text:
central fissure, motor area, auditory area, visual area, fissure of
Sylvius, brain stem, cerebellum)]

In pure cases of _motor aphasia_, the subject knows the words he
wishes to say, but cannot get them out. The brain injury here lies in
the frontal lobe in the left hemisphere, in right-handed people, just
forward of the motor area for the mouth, tongue and larynx. This
"motor speech center" is the best-known instance of a super-motor
center. It cooerdinates the elementary speech movements into the
combinations called words; and perhaps there is no other motor
performance so highly skilled as this of speaking. It is acquired so
early in life, and practised so constantly, that {59} we take it quite
as a matter of course, and think of a word as a simple and single
movement, while in fact even a short word, as spoken, is a complex
movement requiring great motor skill.

There is some evidence that the motor speech center extends well
forward into the frontal lobe, and that the front part of it is
related to the part further back as this is to the motor area back of
it. That is to say, the back of the speech center combines the motor
units of the motor area into the skilled movements of speaking a word,
while the more forward part of the speech center combines the word
movements into the still more complex movement of speaking a sentence.
It is even possible that the very front part of the speech center has
to do with those still higher combinations of speech movements that
give fluency and real excellence of speaking.

The Auditory Centers

Besides the motor aphasia, just mentioned, there is another type,
called _sensory aphasia_, or, more precisely, auditory aphasia. In
pure auditory aphasia there is no inability to pronounce words or even
to speak fluently, but there is, first, an inability to "hear words",
sometimes called word deafness, and there is often also an inability
to find the right words to speak, so that the individual so afflicted,
while speaking fluently enough and having sense in mind, misuses his
words and utters a perfect jargon. One old gentleman mystified his
friends one morning by declaring that he must go and "have his
umbrella w