The principal serous membrane of the thorax; the shut sac, having a serous surface, which lines the walls of the chest, and is reflected over the surface of each lung.In conchology, one of the lateral tracts on each side of the rachis of the lingual ribbon of the odontophore: generally used in the plural.In comparative anatomy, the lateral portion of one of the rings composing the integument of an arthropod or articulate animal, lying between the tergum and sternum, and in insects and crustaceans consisting of two pieces, the epimeron and episternum.All the parts of the pleura except the pulmonary portion.n. Plural of pleuron.