Il6 TOPOGRAPHIC AND APPLIED ANATOMY. 



may perforate : into the trachea or into the left bronchus, into the aortic arch or into the descend- 

 ing aorta, into either of the pleural cavities, or into the pericardium. In this manner air may 

 enter the pleural cavity from the mouth (pneumothorax) and also the pericardium (pneumo- 

 pericardium) as a result of the perforation of a cancer of the esophagus. Stenosis of the esoph- 

 agus may be produced by the pressure of an aortic aneurysm, by enlargements of the bronchial 

 lymphatic glands at the tracheal bifurcation, by carcinoma of the lung or of the pleura, and by 

 tumors in the posterior portion of the mediastinum. Cicatricial contraction of the bronchial 

 lymphatic glands may lead to the formation of the so-called traction diverticula, which are most 

 commonly found in the anterior wall of the esophagus. The mucous and muscular coats of the 

 esophagus are united by a very loose submucous connective tissue; suppuration may extend 

 widely between these layers, and foreign bodies or sounds may perforate the mucosa and make 

 false passages. 



[The veins, especially at the lower end, may be enormously dilated and varicose in case of 

 obstruction to the portal circulation, owing to nature's attempt to create a collateral circulation 

 between the veins of the stomach and those of the esophagus (emptying into azygos and peri- 

 cardiac veins), giving rise, if a rupture occurs, to severe hemorrhage (hematemesis). Eisen- 

 drath.] 



In the lower portion of the mediastinal space the esophagus is accompanied by the two 

 pneumo gastric nerves, which pursue a different course upon the right and the left sides (Plate 

 10). The right pneumogastric nerve enters the mediastinum in front of the right subclavian 

 artery. After giving off the right inferior or recurrent laryngeal nerve, it passes to the right 

 side of the innominate artery ; it then runs alongside of the trachea and behind the right bronchus 

 to the esophagus, which it accompanies through the esophageal opening. The left pneumogastric 

 nerve reaches the left side of the aortic arch between the left common carotid and the left sub- 

 clavian arteries, gives off the left inferior laryngeal nerve (passing backward and upward around 

 the aortic arch), and runs behind the left pulmonary artery and left bronchus to the esophagus. 

 (The visceral branches of the pneumogastric and its communications with the sympathetic 

 plexuses should be reviewed in a systematic anatomy.) 



The pneumogastric nerves descend behind the roots of the lungs, and when the pleura is 

 intact they may both be seen above these structures. The phrenic nerves run downward to the 

 diaphragm beneath the mediastinal pleura and between it and the pericardium ; they are accom- 

 panied by the comes nervi phrenici (branches of the internal mammary artery). The phrenic 

 nerves arise from the cervical plexus and pass through the superior aperture of the thorax between 

 the subclavian artery and vein (see page 71). 



The remaining contents of the mediastinum are the paired vessels in front of the vertebral 

 column, the vena azygos major and vena azygos minor (hemiazygos), and the thoracic duct. 



The Vena Azygos Major. In the abdominal cavity beside the lumbar vertebra, the vena 

 azygos major is connected with the lumbar veins, and through these with the inferior vena cava. 

 (see page 122). The vessel enters the thorax through the right crus of the diaphragm, ascends 

 along the right side of the vertebral column (Plates 8b and 14), receives the intercostal veins, 

 passes over the right bronchus at the third dorsal vertebra, and empties into the posterior portion 

 of the superior vena cava (Fig. 51). By its communication with the inferior vena cava it renders 



