between; consequently when the chest expands in all three directions the
elastic lungs expand correspondingly. But when either voluntarily or
automatically the nerve currents that cause contraction of the muscles of
expansion cease, the elastic structures of the lungs and thorax, including
the muscles, recoil, the diaphragm ascends, and the ribs by the force of
gravity tend to fall into the position of rest. During expansion of the
chest a negative pressure is established in the air passages and air flows
into them from without. In contraction of the chest there is a positive
pressure in the air passages, and air is expelled; in normal quiet
breathing an ebb and flow of air takes place rhythmically and
subconsciously; thus in the ordinary speaking of conversation we do not
require to exercise any voluntary effort in controlling the breathing, but
the orator and more especially the singer uses his knowledge and experience
in the voluntary control of his breath, and he is thus enabled to use his
vocal instrument in the most effective manner.

[Illustration: FIG. 2

Adapted from Quain's "Anatomy" by permission of Messrs. Longmans, Green &
Co.]

[Description: FIG. 2.--Diagram modified from Quain's "Anatomy" to show the
attachment of the diaphragm by fleshy pillars to the spinal column, to the
rib cartilages, and lower end of the breastbone and last rib. The muscular
fibres, intercostals, and elevators of the ribs are seen, and it will be
observed that their action would be to rotate and elevate the ribs. The
dome-like shape of the diaphragm is seen, and it can be easily understood
that if the central tendon is fixed and the sheet of muscle fibres on
either side contracts, the floor of the chest on either side will flatten,
allowing the lungs to expand vertically. The joints of the ribs with the