, of course, be more distinctly
ascertained at the locality of F, the right ventricle, which is
immediately substernal. While the body lies supine, the heart recedes
from the forepart of the chest; and the lungs during inspiration
expanding around the heart will render its sounds less distinct. In the
erect posture, the heart inclines forwards and approaches the anterior
wall of the thorax. When the heart is hypertrophied, the lungs do not
overlap it to the same extent as when it is of its ordinary size. In the
latter state, the elastic cushion of the lung muffles the heart's
impulse. In the former state, the lung is pushed aside by the overgrown
heart, the strong muscular walls of which strike forcibly against the
ribs and sternum.

The thorax is separated from the abdomen by the moveable diaphragm. The
heart, F E, lies upon the diaphragm, L L*. The liver, M, lies
immediately beneath the right side of this muscular septum, L*, while
the bulging cardiac end of the stomach, O, is in close contact with it
on the left side, L. As these three organs are attached to the
diaphragm--the heart by its pericardium, the stomach by the tube of the
oesophagus, and the liver by its suspensory ligaments--it must happen
that the diaphragm while descending and ascending in the motions of
inspiration and expiration will communicate the same alternate motions
to the organs which are connected with it.

In ordinary respiration the capacity of the thorax is chiefly affected
by the motions of the diaphragm; and the relative position which this
septum holds with regard to the thoracic and abdominal chambers will
cause its motions of ascent and descent to influence the capacity of
both chambers at the same time. When the lungs expand, they follow the
descent of the diaphragm, which forces the abdominal contents downwards,
and thus what the thorax gains in space the abdomen loses. When the
lungs contract, the diaphragm ascends, and by this act the abdomen gains
that space which the thorax loses. But the organs of the thoracic cavity
perform a different office in the economy from those of the abdomen. The
air which fills the lungs is soon again expired, whilst the ingesta of
the abdominal viscera are for a longer period retained; and as the
space, which by every inspiration the thorax gains from the abdomen,
would cause inconvenient pressure on the distended organs of this latter
cavity, so we find that to obviate this inconvenience, nature has