The pleural cavity, also known as the pleural sac or pleural space,
is a body cavity that surrounds the lung in humans
and other mammals. It is separated from the
rest of the perivisceral cavity by the diaphragm. There is a pair of pleural
cavities separated from each other by the mediastinum and the pericardial cavity. The
actual space of the pleural cavity is normally filled with a thin layer
of fluid between the pleura of the lungs
and the body wall, which are almost in contact.