bral hemispheres from which the nerves of speech are
excited and to which the sense-impressions from without are so conducted
by connecting fibers that they themselves or their memory-images can
call forth expressive, i. e., motor processes. The diagram, Fig. 1,
illustrates the matter.

[Illustration: FIG. 1.]

The peripheral ear _o_, with the terminations of the auditory nerve, is
by means of sensory fibers _a_, that are connected with the auditory
nerve, in connection with the storehouse of sound-impressions, K. This
is connected by means of the intercentral paths _v_ with the motor
speech-center M. From it go out special fibers of communication, _h_, to
the motor nerves of speech which terminate in the external instruments
of articulation, _z_.

The impressive nerve-path, _o_ _a_ K, is centripetal; the expressive,
M _h_ _z_, centrifugal; _v_, intercentral.

When the normal child learns to speak, _o_ receives the
sound-impressions; by _a_ the acoustic-nerve excitations are passed
along to K, and are here stored up, every distinctly heard sound (a
tone, a syllable, a word) leaving an impression behind in K. It is
very remarkable here that, among the many sounds and noises that
impress themselves upon the portions of the brain directly connected
with the auditory nerve, a selection is made in the sound-field of
speech, K, since all those impressions that can be reproduced, among
them all the acoustic images necessary for speech, are preserved, but
many others are not, e. g., thunder, crackling. Memory is indistinct
with regard to these. From K, when the sound-images or
sound-impressions have become sufficiently strong and numerous, the
nerve-excitement goes farther through the connecting paths _v_ to M,
where it liberates motor impulses, and through _h_ sets in activity
the peripheral apparatus of speech, _z_.

Now, speech is disturbed when at any point the path _o_ _z_ is
interrupted, or the excitation conducted along the nerve-fibers and
ganglionic cells upon the hearing of something spoken or upon the
speaking of something represented in idea (heard inwardly) is arrested,
a thing which may be effected without a total interruption of the
conduction, e. g., by means of poison and through anatomical lesions.

On the basis of these physiological relations, about which there is no
doubt, I divide, then, all pure disturbances of speech, or
_lalopathies_, into three classes:

(1) Periphero-Impressive or Perceptive