THE PLEURA 



1237 



The parietal pleura [pleura parietalis] is divided, according to the regions of the chest with 

 which it is associated, into the costal, diaphragmatic, and mediastinal pleura. The costal 

 pletira [pleura costahs] lines the thoracic wall, to which it is bound not very firmly by the 

 endothoracjc fascia. It covers incompletely the back of the sternum and extends laterally upon 

 the ribs and intercostal muscles. Posteriorly beyond the angles of the ribs it passes over the 

 anterior rami of the thoracic nerves and intercostal vessels, the heads of the ribs, and the 

 sympathetic trunk to the vertebral column; here it becomes continuous with the mediastinal 

 pleura. Above, the pleura reaches beyond the superior margin of the sternum into the root of 

 the neck, and in the form of a dome, the cupola of the pleura [cupola pleurae], is adapted to the 

 apex of the lung. It is supported by processes of the deep cervical fascia, and by a fibrous 

 aponeurosis known as Sibson's fascia, coming from the scalenus minimus muscle and connected 

 with the inner margin of the first rib. In relation to the pleural cupola are those structures 

 already described as grouped about the lung apex: the brachial plexus, subclavian artery, ante- 

 rior scalene muscle, and the subclavian vein, and, on the left side, in addition, the thoracic duct. 



Below, the costal pleura is continuous with the diaphragmatic pleura [pleura diaphragmatica], 

 which adheres closely to the thoracic surface of the diaphragm and covers it, excepting the 

 pericardial area and where the diaphragm and thoracic wall are in contact. 



The mediastinal pleura [pleura mediastinalis] is reflected from before backward at the 

 right and left sides of the mediastinum as the laminae mediastinales, covering the pericardium 



Fig. 1000. — Right Lateral Surface of the Mediastinum after Removal of the Pleura. 



(Poirier and Charpy.) 



Trachea . 



Azygos vein 



Phrenic nerve 



[pleura pericardiaca], to which it is closely adherent, and also the other structures of 

 the mediastinum, with which the two layers are less firmly connected. Above the lung root 

 the mediastinal pleura stretches directly from the spine to the sternum; but at the level of the 

 root and below it, it is reflected laterally to the pulmonary pleura covering the root in front and 

 behind and forming the pulmonary ligament. 



The right mediastinal lamina covers (fig. 1000) the right innominate vein, the superior vena 

 cava, the vena azygos, the trachea, the innominate artery, the right vagus and phrenic nerves, 

 and the oesophagus. The left lamina lies against the left innominate vein, the arch of the aorta 

 the left subclavian artery, the thoracic aorta, the left phrenic and vagus nerves, and the oesoph- 

 agus. About the base of the heart-sac are a number of adipose folds [plicaj adiposae) projecting 

 from the pleura, the surfaces of which present some villous processes, the pleural villi [villi 

 pleurales] ; the latter also occur on the pulmonary pleura along the inferior margin of the lung. 



The lines of pleural reflexion are of practical importance (figs. 997, 998, 1003). Posteriorly, 

 the costal pleura simply turns forward in a gentle curve to become the mediastinal pleura, but 

 anteriorly and inferiorly the membrane is folded upon itself, leaving intervening capillary 

 spaces, the sinuses of the pleura [sinus pleurae]. Such a space is present where the costal pleura 

 is reflected upon the diaphragm, the sinus phrenicocostalis, the fold of the pleura occupying 

 the upper part of the angle between the thoracic wall and diaphragm, the endothoracic fascia 



