Related to the thoracic (throat, chest) pleura (membrane enveloping the lungs and the linings of the walls of the pulmonary cavities): Each lung is enveloped in a double-folded membrane called the pleura where the outer part which is closest to the ribs, is the parietalpleura; and the inner layer, closest to the lung, is the visceralpleura.

The visceralpleura or pleurovisceraland the parietalpleura are moistened with a serous (thin, watery fluid) secretion that facilitates the movements of the lungs within the chest (thorax).