The pleura is the serous membrane that lines the inner surface of the hemithorax and covers the lung in continuity by folding back around the pulmonary hilum. The pleura envelops the pulmonary hilum and extends downward as a double layer from the inferior aspect of the mediastinal surface of the lung to the pericardium and ends in a free border inferiorly. This fold is referred to as the pulmonary ligament and contains lymphatic vessels from the pleura of the lower lobe that course toward the posterior mediastinal nodes.Covering the lung surface is the visceral pleura. The parietal pleura lines the inner surface of the hemithorax. Costal, diaphragmatic, mediastinal, and apical or cervical regions are noted according to their locations. The costal pleura is attached to the endothoracic fascia from which it is easily separated. The diaphragmatic pleura covers the superior surface of the diaphragm except for the area that abuts the pericardium. It is connected to and difficult to separate from the diaphragmatic musculature.The pleura descends to the level of the 12th rib posteriorly, to the level of the 6th costal cartilage anteriorly, and crosses the levels of the 7th to 11th ribs laterally where the costal and diaphragmatic pleural surfaces are in contact and form the costodiaphragmatic angle.Extending above the first rib and clavicle is the dome-shaped apical pleura, which is surrounded and supported by the suprapleural membrane (Sibson's fascia) and is in direct contact with the deep cervical fascia, the subclavian artery, and the subclavian vein. Because of this topographic relationship, the apical pleura may be easily entered during operations at the base of the neck, with resulting pneumothorax or hemopneumothorax.The mediastinal pleura extends from each side of the thoracic spine to the posterior surface of the sternum and is interrupted by the pulmonary hilum and the attachment of the pulmonary ligament. At these sites, the mediastinal pleura folds, covers the hilum, forms the pulmonary ligament, and continues as the visceral pleura.The right mediastinal pleura comes in contact with the superior vena cava, the innominate vein, the innominate artery, the azygos vein, the right side of the trachea, the right vagus and phrenic nerves, and the right side of the pericardium. The left mediastinal pleura covers part of the aortic arch, the left phrenic and vagus nerves, the left superior intercostal vein, left common carotid and left subclavian arteries, the esophagus, the thoracic duct, and the left side of the pericardium.Arterial blood supply to the parietal pleura consists of branches of the adjacent arteries. The intercostal, internal mammary, pericardial, and superior phrenic arteries contribute branches supplying the pleura. Arterial supply to the visceral pleura consists of radicles of the bronchial and pulmonary arteries. Venous drainage of the pleura corresponds to its arterial supply except for the bronchial arteries, which do not have corresponding veins, resulting in visceral pleural venous drainage v...