association with that of the tongue, lips, and jaw. This is as we should
expect, for they form a part of the whole cerebral mechanism which presides
over the voice in speech and song. But because the muscles of the tongue,
the lower face muscles, and even the muscles of the jaw do not necessarily
and always work synchronously and similarly on the two sides, there is more
independence in their representation in the cerebral cortex. Consequently a
destruction of this region of the brain or the fibres which proceed from it
to the lower executive bulbar and spinal centres is followed by paralysis
of the muscles of the opposite side. Likewise stimulation with an
interrupted electric current applied to this region of the brain in monkeys
by suitable electrodes produces movements of the muscles of the lips,
tongue, and jaw of the opposite side only. Not so, however, stimulation of
the region which presides over the movements of the muscles of the larynx,
for then _both_ vocal cords are drawn together and made tense as in
phonation. It is therefore not surprising if removal or destruction of this
portion of the brain _on one side_ does not produce paralysis of the
muscles of phonation, which, always bilaterally associated in their
actions, are represented as a bilateral group in both halves of the brain.
These centres may be regarded as a part of the physiological mechanism, but
the brain acts as a whole in the psychic mechanism of speech and song. From
these facts it appears that there is: (1) An automatic mechanism for
respiration and elemental phonation (the cry) in the medulla oblongata
which can act independently of the higher centres in the brain and even
without them (_vide_ p. 18). (2) A cerebral conscious voluntary mechanism
which controls phonation either alone or associated with articulation. The
opening of the glottis by contraction of the abductor (posterior
ring-pyramid muscles) is especially associated with descent of the
diaphragm in inspiration in ordinary breathing; whereas the voluntary
breathing in singing is associated with contraction of the adductor and
tensor muscles of the vocal cords.