The pleura-like peritoneum is a serous membrane lined by flattened epithelium (mesothelium). The lining epithelium secretes a watery lubricant—the serous fluid.
LAYERS OF THE PLEURA The pleura consist of two layers: (a) visceral pleura and (b) parietal pleura. The moistened space between the two layers is called pleural cavity (vide supra). Visceral Pleura (Pulmonary Pleura) The visceral pleura completely covers the surface of the lung except at the hilum and along the attachment of the pulmonary ligament. It also extends into the depths of the fissures of the lungs. It is firmly adherent to the lung surface and cannot be separated from it. Parietal Pleura The parietal pleura is thicker than the visceral pleura and lines the walls of the pulmonary cavity. Subdivisions For the purpose of description, it is customary to divide parietal pleura, according to the surface, which it lines, covers or the region in which it lies.
Thus parietal pleura is divided into the following four parts: 1. Costal pleura. 2. Diaphragmatic pleura. 3. Mediastinal pleura. 4. Cervical pleura. Costal pleura: It lines the inner surface of the thoracic wall (consisting of ribs, costal cartilages, and intercostal spaces) to which it is loosely attached by a thin layer of loose areolar tissue called endothoracic fascia. In living beings, endothoracic fascia is easily separable from the thoracic wall. Diaphragmatic pleura: It covers the superior surface of the diaphragm. In quiet respiration, the costal and diaphragmatic pleura are in opposition to each other below the inferior border of the lung. Mediastinal pleura: It lines the corresponding surface of the mediastinum and forms its lateral boundary. It is reflected as a cuff over the root of the lung and becomes continuous with the visceral pleura. Cervical pleura: It is the dome of parietal pleura, which extends into the root of the neck about 1 inch (2.5 cm) above the medial end of clavicle and 2 inches (5 cm) above the 1st costal cartilage.