The pulmonary pleurae (sing. pleura)[1] are the two pleurae of the invaginated sac surrounding each lung and attaching to the thoracic cavity. The visceral pleura is the delicate serous membrane that covers the surface of each lung (the lung parenchyma) and dips into the fissures between the lobes.[2] The parietal pleura is the outer membrane which is attached to the inner surface of the thoracic cavity. It also separates the pleural cavity from the mediastinum.