The Bronchial Arteries arise from the anterior part of the aorta; they are amongst the most irregular in the body, and can only be recognized by their termination in the lung, and not by their origin, as they may arise from the aorta, the intercostals, the mammary, or even from the subclavian arteries. Those most constantly found are three in number; viz., one on the right side; and two on the left,—a superior and an inferior.

The right bronchial artery sometimes comes from the aorta, in common with the left, or separately: usually, however, it is a branch of the first aortic intercostal: in all cases it descends on the back of the right bronchus, and, winding round it, accompanies it into the lung: the superior left bronchial artery usually comes from the aorta, and in a similar manner twines round the left bronchus, and with it enters the lung: the left inferior bronchial artery often arises from the aorta, opposite the third or fourth dorsal vertebra, and is conducted to the left lung by the left superior pulmonic vein : it is not as constant as the two preceding. Arrived at the lung, the right bronchial artery usually divides into five branches, and the left into four: these subdivide, and accompany the divisions of the bronchi through the lung, in such a manner, however, that one division of the bronchus has usually with it two or three arterial branches, which, frequently anastomosing, form a delicate net-work round the air-vessel. The bronchial arteries communicate with the other blood-vessels of the lung.

Two or three other bronchial arteries may arise occasionally from the concavity of the arch of the aorta, and also repair to the lung.

The (Esophageal arteries, three to six in number, arise from the anterior part of the thoracic aorta, at variable points: they are lost in the tunics of the oesophagus, and in anastomosing with the inferior branches of the inferior thyroid artery, and with the oesophageal branches of the gastric artery. They are always very small, and the highest of them occasionally comes from one of the bronchial arteries.

The Posterior Mediastinal Branches

The Posterior Mediastinal Branches are small and numerous : they arise from various parts of the thoracic aorta, and supply the glandular structures and areolar tissue contained in the posterior mediastinum.