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. 16). Whatever its situation, it must be connected by association fibres with the centres of phonation and articulation. [Illustration: FIG. 18] [Description: FIG. 18.--The accompanying diagram is an attempt to explain the course of innervation currents in phonation. 1. Represents the whole brain sending voluntary impulses _V_ to the regions of the brain presiding over the mechanisms of voluntary breathing and phonation. These two regions are associated in their action by fibres of association _A_; moreover, the corresponding centres in the two halves of the brain are unified in their action by association fibres _A'_ in the great bridge connecting the two hemispheres (Corpus Callosum). On each side of the centre for phonation are represented association fibres _H_ which come from the centre of hearing; these fibres convey the guiding mental images of sounds and determine exactly the liberation of innervation currents from the centre of phonation to the lower centres by which the required alterations in tension of the laryngeal muscles for the production of the corresponding sounds are effected. Arrows are represented passing from the centre of phonation to the lower centres in the medulla which preside over the muscles of the jaw, tongue, lips, and larynx. Arrows indicate also the passage of innervation currents from the centres in the brain which preside over voluntary breathing. It will be observed that the innervation currents which proceed from the brain pass over to the opposite side of the spinal cord and are not represented as coming into relation with the respiratory centre _R_. This centre, as we have seen, acts automatically, and exercises especially its influence upon the diaphragm, which is less under the control of the will than the elevators of the ribs and the abdominal muscles.