Of these the employment of the diaphragm as a voluntary muscle is probably the most important. When the diaphragm acts in this way, in addition to its descent which is the more obvious result, the lower ribs are elevated, increasing the transverse diameter of the body at this level, this providing additional space at that part of the abdominal cavity for the viscera displaced by the descent of the diaphragm. Simultaneously the muscles of the abdominal wall come under the sphere of influence. In the breathing of repose the tonus of the broad muscles of the abdomen is such as just to admit of the necessary bulging forward which is determined by the downward displacement of the abdominal contents by the contracting diaphragm. In breathing for voice this tonus is increased, as can readily be appreciated by palpation. The effect of this hardening of the abdominal wall cbecks the outward bulging (which is no longer necessary), and by steadying the lower part ot the chest takes a share in the control of expirati0n. Regarding the other factors concerned in the control of expiration, the subcommittee are of opinion that further investigations must be undertaken before any authoritative pronouncement can be made.
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