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Other Terms: Bronchus principalis, Primary bronchus, Principal bronchus
The bronchi are the two branches of the trachea at its bifurcation that allow air passage to each lung. They occupy the middle mediastinum. The differences between the two bronchi may be summed up as follows: the right bronchus is about two and a half centimeters (one inch) long, is shorter and more horizontal than the left, and has a larger diameter; the left bronchus is about five centimeters (two inches) long, narrower, and more vertical than the right. The two bronchi diverge at an angle of about 130 degrees. The right bronchus has, arching over it from behind, the azygos vein on its way to the superior vena cava, while the horizontal right pulmonary artery lies at first below, and then anterior to the bronchus; below the first division of the right bronchus the pulmonary artery lies posterior to the bronchus. The left bronchus crosses anterior to the esophagus, the thoracic duct, and the descending aorta, under the transverse aorta, and lies behind the left pulmonary artery. The orifice of the right bronchus being larger than that of the left and placed nearly under the center of the trachea, foreign bodies usually enter the right bronchus. In certain cases of aneurysm of the transverse and the beginning of the descending aorta the pulsation of the aneurismal sac leads to depression of the left bronchus, with consequent downward movement of the trachea. If in such cases the larynx is lightly grasped between the thumb and finger, this traction upon the trachea, synchronous with the systole of the heart, is felt. This sign is known as the "tracheal tug." Foreign bodies entering the air-passages may lodge in the larynx, in the trachea, or may enter one of the bronchi, usually the right one because of the larger diameter.