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.
A perfect psychic mechanism is as necessary as the physiological mechanism
for the production of perfect vocalisation, especially for dramatic
singing.
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