Both sets would be affected by the lesion (or damage)
which produced the hemiplegia. The inhibitory fibres being damaged, the
opposite half of the respiratory centre would be under diminished control
and therefore the movements of ordinary breathing on the paralysed side
would be exaggerated. The damage to the direct fibres would prevent the
passage of voluntary stimuli to the groups of respiratory muscles (as it
would do to the rest of the muscles of the paralysed side), and thus the
voluntary movement of respiration would be diminished--diminished only and
not completely abolished as in the limbs; because according to the theory
of Broadbent, in the case of such closely associated bilateral movements
the lower nervous respiratory centres of both sides would be activated from
either side of the brain." This certainly applies also to the muscles of
phonation, but not to the principal muscles of articulation, viz. the
tongue and lips. It is not exactly known what part of the cerebral cortex
controls the associated movements necessary for voluntary costal (rib)
respiration in singing; probably it is localised in the frontal lobe in
front of that part, stimulation of which gives rise to trunk movements
(_vide_ fig.
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