252 HUMAN ANATOMY. 



Anteriorly. 

 Sternum ; 



Remains of thymus; 

 Arch of aorta; 



Right and left innominate veins; 

 Left carotid artery; 

 Deep cardiac plexus. 



Posteriorly. 

 (Esophagus. 



The arteries are derived from the inferior thyroid and bron- 

 chial. 



The veins empty into the thyroid and bronchial plexuses. 



The nerves are from the pneumogastric and sympathetic. 



The lymphatics empty into the mediastinal glands. 



The bronchi are the continuation of the trachea from its 

 bifurcation to the hilus of the lung. 



Right bronchus is shorter, about one inch in length, placed 

 more horizontally, and wider. It divides at the hilus into three 

 short branches, corresponding to the divisions of the right lung. 



Left bronchus is longer, nearly two inches in length, placed 

 more obliquely, and narrower than the right. It divides into 

 two long branches corresponding to the number of lobes : 



Relations. The right bronchus has the right auricle and the supe- 

 rior vena cava in front of it, the right pulmonary artery at first below, 

 then passing also in front, and the vena azygos arching over it from 

 behind; 



The left bronchus has the arch of aorta above, the left pulmonary 

 artery at first above, then in front, and the oesophagus, thoracic duct 

 and descending aorta behind. 



The arteries, veins, nerves, and lymphatics are the same as 

 for the trachea. 



The two bronchi subdivide into the bronchial tubes, or bron- 

 chioles, which ramify throughout the lungs, dividing and sub- 

 dividing, to end finally in the primary lobules, where they 

 communicate with the intercellular air-passages. Their carti- 

 lages consist of thin plates, distributed irregularly along the 

 tubes, and in the finer tubes disappearing entirely. The mucous 

 membrane of the bronchi and bronchial tubes is lined throughout 

 with columnar ciliated epithelium. 



THE LUNGS. 



The lungs, the organs of respiration, are two in number, 

 occupying the lateral cavities of the chest, separated from each 

 other by the heart and structures within the mediastinum. They 



