om the
cavity of the pleura.

The permanent distention of the thoracic cavity, caused by the
accumulation of air in the pleural sac, or by the diffusion of air
through the interlobular cellular tissue consequent on a wound of the
lung itself, will equally obstruct the breathing; and though the
situation of the accumulated air is in fact anatomically different in
both cases, yet the effect produced is similar. Interlobular pressure
and interpleural pressure result in the same thing, viz., the permanent
retention of the air external to the pulmonary cells, which, in the
former case, are collapsed individually; and, in the latter case, in the
mass. Though the emphysematous lung is distended to a size equal to the
healthy lung in deep inspiration, yet we know that emphysematous
distention, being produced by extrabronchial air accumulation, is, in
fact, obstructive to the respiratory act. The emphysematous lung will,
in the same manner as the distended pleural sac, depress the diaphragm
and render the thoracic muscles inoperative. The foregoing observations
have been made in reference to the effect of wounds of the thorax, the
proper treatment of which will be obviously suggested by our knowledge
of the state of the contained organs which have suffered lesion.

DESCRIPTION OF PLATE 23.

A. Upper end of the sternum.

B B.* First pair of ribs.

C C.* Second pair of ribs.

D. Aorta, with left vagus and phrenic nerves crossing its transverse
arch.

E. Root of pulmonary artery.

F. Right ventricle.

G. Right auricle.

H. Vena cava superior, with right phrenic nerve on its outer border.

I I*. Right and left lungs collapsed, and turned outwards, to show the
heart's outline.

K K*. Seventh pair of ribs.

L L*. The diaphragm in section.

M. The liver in section.

N. The gall bladder with its duct joining the hepatic duct to form the
common bile duct. The hepatic artery is seen superficial to the common
duct; the vena portae is seen beneath it. The patent orifices of the
hepatic veins are seen on the cut surface of the liver.

O. The stomach.

P. The coeliac axis dividing into the coronary, splenic and hepatic
arteries.

Q. Inferior vena cava.

R. The spleen.

S S* S**. The transverse colon, between which and the lower border of
the stomach is seen the gastro-epiploic artery, formed by
the splenic and hepatic arteries.

S***. Ascending colon in the right iliac regi