There is another region connected with the memory
of spoken words--the _auditory word-centre_; you will observe that it is
situated in the posterior third of the first temporal convolution, but this
does not comprise nearly the whole of it, for there is an extensive surface
of grey matter lying unseen within the fissure, called the transverse
convolutions, or gyri. Lesions of either of these regions give rise to
_Sensory Aphasia_, which means a loss of speech due to inability to revive
in memory the articulate sounds which serve as verbal symbols, or the
graphic signs which serve as visual symbols for language.
[Illustration: FIG. 17]
[Description: FIG. 17.--Diagram to illustrate the Speech Zone of the left
hemisphere (Bastian). This scheme is used to explain the mechanism of
speech, but probably the centres are not precisely limited, as shown in the
diagram; it serves, however, to explain disorders of speech. Destruction of
the brain substance in front of the central fissure gives rise to what is
termed Motor Aphasia and Motor Agraphia, because the patient no longer
recalls the images of the movements necessary for expressing himself in
articulate speech or by writing. Destructive lesions behind the central
fissure may damage the portion of the brain connected with the mental
perception of the sounds of articulate language, or the portion of the
brain connected with the mental perception of language in the form of
printed or written words--Sensory Aphasia; the former entails inability to
speak, the latter inability to read.
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