rnal ribs, and yet will not be therefore proof positive that the
liver is diseased and abnormally enlarged. Whereas, on the other hand,
when G, the liver, is actually diseased, it may occupy a situation in
the right side as high as the fifth or sixth ribs, pushing the right
lung upwards as high as that level; and, therefore, while percussion
elicits a dull sound over this place thus occupied, such sound will not
be owing to a hepatized lung, but to the absence of the lung caused by
the presence of the liver.

In the healthy adult male body, Plate 22, the two lungs, D D*, whilst in
their ordinary expanded state, may be said to range over all that region
of the trunk of the body which is marked by the sternal and asternal
ribs. The heart, E, occupies the thoracic centre, and part of the left
thoracic side. The heart is almost completely enveloped in the two
lungs. The only portion of the heart and pericardium, which appears
uncovered by the lung on opening the thorax, is the base of the right
ventricle, E, situated immediately behind the lower end of the sternum,
where this bone is joined by the cartilages of the sixth and seventh
ribs. The lungs range perpendicularly from points an inch above B, the
first rib, downwards to L, the tenth rib, and obliquely downwards and
backwards to the vertebral ends of the last ribs. This space varies in
capacity, according to the degree in which the lungs are expanded within
it. The increase in thoracic space is attained, laterally, by the
expansion of the ribs, C I; and vertically, by the descent of the
diaphragm, H, which forces downwards the mass of abdominal viscera. The
contraction of thoracic space is caused by the approximation of all the
ribs on each side to each other; and by the ascent of the diaphragm. The
expansion of the lungs around the heart would compress this organ, were
it not that the costal sides yield laterally while the diaphragm itself
descends. The heart follows the ascent and descent of the diaphragm,
both in ordinary and forced respiration.

But however much the lungs vary in capacity, or the heart as to position
in the respiratory motions, still the lungs are always closely applied
to the thoracic walls. Between the pleura costalis and pulmonalis there
occurs no interval in health. The thoracic parietes expand and contract
to a certain degree; and to that same degree, and no further, do the
lungs within the thorax expand and contract. By no effort of expiratio