Pleura

The pleurae form a casing around the lungs, on the outer edge of the thoracic cavity. Each pleura has two parts, the parietal layer (on the outside) and the visceral pleura (on the inside). In between the layers is the pleural cavity with contains pleural fluid, which covers both as a thin film, and permits the two to move against each other with minimum friction. The two pleurae join at the hilum.