408 SPLANCHNOLOGY, OR' ANATOMY OF THE VISCERA 



contains the origins of the triangularis sterni, the left internal 

 mammary vessels, some areolar tissue containing lymphatics, 

 and the anterior mediastinal glands. 



The middle mediastinum contains the heart and pericardium, 

 ascending aorta, superior vena cava (lower half), inferior 

 vena cava (upper part), bifurcation of trachea, pulmonary 

 vessels, the phrenic nerves, the deep cardiac plexus, the vena 

 azygos major vein, as it arches over the right bronchus to 

 open into the superior vena cava. Some bronchial lymph 

 nodes are also found in this space. 



The posterior mediastinum is behind the pericardium and 

 roots of the lungs, and in front of the lower eight dorsal vertebra*, 

 the pleurae bounding it on each side, the posterior surface of 

 the diaphragm below. It contains the descending part of the 

 arch, the thoracic aorta, the azygos veins, and vagi, and the 

 splanchnic nerves, esophagus, thoracic duct, and some lymphatic 

 glands. 



THE LUNGS (PULMONES) 



The lungs are the essential organs of respiration; they are 

 situated in the right and left sides of the thorax, covered by 

 the visceral portion of the pleura; filling the cavity, with the 

 exception of the intervening mediastinum, containing the 

 heart, surrounded by the pericardium, the aorta, pulmonary 

 artery, esophagus, thoracic duct, precava and postcava, and 

 the nerves, arteries, and veins, which pass toward and away 

 from the interlying structures. 



Each lung presents for examination an apex, a base, dia- 

 phragmatic, costal, mediastinal surfaces, and anterior, posterior, 

 and inferior borders. It is suspended within the cavity, by 

 the root and the ligamentum pulmonale. During respiration 

 the lung, covered by the visceral pleura, is pressed against the 

 walls of the thorax interlined by the parietal pleura, and friction 

 is prevented by a small amount of fluid, within the pleural 

 cavity which continually bathes the approximating surfaces. 



The apex (apex pulmonis) is rounded, and extends about one 

 inch to two inches above the anterior end of the first rib. 

 It is grooved by the subclavian artery on the left side, but 

 on the right side the impression of the innominate vein is the 

 most prominent groove seen. 



