The right bronchial artery most usually arises from the first aortic intercostal artery of the right side, which supplies it after having arrived at the right side of the spinal column behind the oesophagus, sometimes it comes direct from the aorta; it proceeds in a tortuous course under the right bronchus, to the root of the right lung, after having given small branches to the oeso phagus, the pleura, the back part of the peri cardium and the bronchial glands.
The left bronchial artery arises immediately from the aorta and passes in front of the oeso phagus to the left bronchus, to the posterior side of which it attaches itself. Both bronchial arteries are similarly distributed through the lungs, dividing with the bronchi, along each branch of which they send two or more tortu ous twigs. The relation of the bronchial arte ries to the other vessels of the lungs will be more particularly noticed in the article LUNG.
The esophageal arteries vary in number from two to seven : they are inferior to the bronchial in size : they arise from the front of the thoracic aorta, and are distributed to the oesophagus, on which they anastomose freely with descending branches of the inferior thyroid from above, in the middle of the oesophagus with the bronchial, and below with branches of the phrenic and coronary artery of the stomach.
The posterior mediastinal arteries are nume rous and small; they . send branches to the oesophagus, thoracic aorta, thoracic duct, ab sorbents, and cellular membrane of the pos terior mediastinum, anastomosing with the bronchial, oesophageal, and some branches of the right thoracic intercostal arteries.
Inferior or aortic intercostal arteries.—Of the eleven intercostal spaces the two superior are mostly supplied with arteries from the superior intercostal branch of the subclavian ; and as the first aortic intercostal artery frequently supplies the third and fourth intercostal spaces, we often meet with but eight pairs of intercostal arteries coming immediately from the aorta (fig. 78, d). The first right aortic intercostal is usually the largest of the series in consequence of giving origin to the right bronchial ; the size of the inter costal arteries diminishes in general from above downwards. All the intercostal arteries arise rather from the posterior part of the aorta, those of opposite sides arising very near each other, and sometimes springing from a common trunk. At first they descend obliquely on the vertebral column, at an acute angle to the trunk of the aorta. The right intercostal arteries are longer
than the left, in consequence of the position of the thoracic aorta on the left side of the spine. Each artery is lodged at first in a groove on the side of the body of each vertebra, enters the intercostal space passing behind the ganglia of the sympathetic nerve, and immediately divides into two branches, one posterior or dorsal, the other anterior or intercostal. The posterior branch passes backwards through a space above the neck of each rib and below the tranverse process of the superior of the two vertebrae, with which the head of the rib is articulated ; it gives some branches to the bodies of the ver and in passing the intervertebral hole it sends branches inwards to the spinal cord, which anastomose with the spinal arteries. The continuation of the vessel is distributed to the longissim us dorsi, sacro-lumbalis, and other muscles along the side of the spine, as well as to the integuments of the back. The ante rior or proper intercostal branch is usually larger than the posterior, and traverses the intercostal space. At first it is situated be tween the pleura and external intercostal muscle, it shortly divides into two smaller branches, a superior and an inferior, which get between the two layers of intercostal muscles. The inferior branch, usually the smaller, runs forwards along the superior border of the in ferior rib, and passes obliquely over its surface to the periosteum covering it. The superior branch, larger than the former, enters a groove in the lower edge of the superior rib, about its angle, in company with the intercostal nerve, and passes forwards between the two layers of intercostal muscles, towards the junction of the rib with its cartilage, where it descends from the rib towards the middle of the intercostal space, and there anastomoses with the anterior intercostal arteries sent off from the internal mammary. Besides supplying the intercostal muscles, pleura, and ribs, the intercostal arteries give several branches, which pierce the external layer of intercostal muscles, and carry blood to the muscles and integuments covering the thorax. The lower intercostals also send branches to the abdominal muscles, diaphragm, and quadratus lumborum, which freely anastomose with the internal mammary, epigastric, phrenic, lumbar, and circumflex iliac arteries.