s of expiration are the four
sets of abdominal muscles and the intercostal muscles that depress the
ribs. The diaphragm is _not_ a muscle of _expiration_.

THE DIAPHRAGM

The diaphragm is in form like an inverted bowl (Fig. 8). It forms the
floor of the thorax (chest) and the roof of the abdomen. It is
attached by a strong tendon to the spinal column behind, and to the
walls of the thorax at its lowest part, which is below the ribs. In
front its attachment is to the cartilage at the pit of the stomach. It
also connects with the transverse abdominal muscle. The diaphragm
being convex, in inspiration the contraction of its fibres flattens it
downward and presses down the organs in the abdomen, thus increasing
the depth of the thorax. Expiration depends wholly on other muscles.

[Illustration: FIGURE 8.]

The muscles so far mentioned are all that need "conscious education;"
the others will act with them voluntarily, automatically. The
abdominal muscles relax during inspiration and the diaphragm relaxes
during expiration, thus rendering the forces nearly equal, though the
strength is in favor of the expiratory muscles. This is what is
needed, for the breath while speaking or singing must go out under
much greater tension than is necessary for inhalation. Inspiration
should be as free as possible from obstruction when singing or
speaking. Expiration must be under _controlled_ pressure.

THE LUNGS

The lungs are spongy bodies which have no activity of their own beyond
a little elasticity. They are controlled by the muscles of
respiration.

Figure 8 shows the organs of the body in their natural positions. The
diaphragm is relaxed and curved upward, as in expiration. During
inspiration the diaphragm is drawn down until it lies nearly flat.

INSPIRATION

The intercostal muscles raise the ribs. The diaphragm is drawn down by
contraction, thus adding to the enlargement of the chest by increasing
its depth. The abdominal muscles relax and allow the stomach, liver,
and other organs in the abdomen to move downward to make room for the
depressed diaphragm. This causes a vacuum in the chest. The lungs
expand to fill this vacuum and the air rushes in to fill the expanding
lungs.

EXPIRATION

The intercostal, and a part of the abdominal, muscles depress the ribs
and lessen the chest cavity anteriorly and laterally. The abdominal
muscles compress the abdomen and force up the diaphragm which is now
relaxed, thus les