The internal thoracic artery arises from the first part of the subclavian artery at the medial border of the anterior scalene, opposite the origin of the thyrocervical trunk. It enters the thorax, lying between the cartilage of the first rib and the parietal layer of the pleura. The artery descends in almost a straight line vertically downward, crossing the interspaces on the medial surface of the thoracic wall, about twelve millimeters from the sternal margin. At the sixth intercostal space, the artery divides into its terminal branches: the superior epigastric and the musculophrenic arteries. The internal thoracic artery consists of a cervical and a thoracic portion. The cervical portion is short and extends from the origin of the artery to the upper border of the first costal cartilage. The thoracic portion begins at the upper border of the first costal cartilage and ends at the division of the artery into its terminal branches at the sixth costal cartilage. The branches of the internal thoracic artery are: the superior phrenic, the mediastinal, the pericardiac, the sternal, the anterior intercostals, the perforating, the lateral infracostal, the superior epigastric, and the musculophrenic. The superior phrenic artery is given off behind the first costal cartilage, and accompanies the phrenic nerve to the diaphragm. It comes in relation with the pleura to the lateral side and with the brachiocephalic vein, the superior vena cava, and the pericardium to the medial side, in its course to the diaphragm. It gives off branches to both pleura and pericardium. It anastomoses with the other phrenic arteries in the diaphragm. It also sends two branches into each of the seventh, eighth and ninth intercostal spaces. The mediastinal branches are small. They supply the fat and areolar tissues and lymphatics in the superior and anterior mediastinal spaces, and the remains of the thymus gland. The pericardiac branches supply a portion of the pericardium. The sternal branches enter the nutrient foramina of the sternum and supply the transversus thoracis muscle. The anterior intercostal arteries arise from the internal thoracic artery in the upper five or six interspaces. In each of the interspaces, one artery passes along the upper border of the rib below and another along the lower border of the rib above. These arise separately from the internal thoracic or the musculophrenic artery, which then divides into the branches described. These branches follow the course of the ribs and anastomose after piercing the internal intercostal muscle in the first interspace with the branches of the costocervical trunk, and in the other interspaces with the aortic intercostal arteries. At first these arteries lie between the internal intercostal muscles and the pleura. Later, they are between the external and internal intercostal muscles, which they supply along with the ribs. The perforating branches arise from the front of the internal thoracic artery and pierce the internal intercostal and pectoralis major muscles to supply the internal intercostals and the skin and fascia over that region. There are usually five or six of them, one for each of the upper interspaces. The second perforating artery is probably the largest. The second, third, and fourth perforating arteries supply the mammary gland and become very enlarged during lactation. . The lateral infracostal artery arises near the first rib and descends behind the ribs just outside their junction with the costal cartilages. It is small and not constant. It anastomoses with the upper intercostal arteries. The superior epigastric artery, one of the terminal branches of the internal thoracic artery, is the direct continuation of it. It leaves the thorax by passing downward posterior to the seventh costal cartilage or to the xiphoid cartilage and through the space between the costal and sternal attachments of the diaphragm. It then enters the sheath of the rectus abdominis muscle. It anastomoses with branches of the inferior epigastric artery. This forms the longest anastomosis in the body. It gives off some small branches to the diaphragm; a xiphoid branch, which anastomoses with the same branch of the opposite side; a few cutaneous branches; muscular branches to the rectus abdominis muscle; several small hepatic branches that reach the liver by running along the falciform ligament and anastomose with the hepatic artery, and some peritoneal branches, which pierce the posterior wall of the sheath of the rectus abdominis muscle and supply the peritoneum. The musculophrenic artery is the other terminal branch of the internal thoracic artery. It pierces the diaphragm at about the eighth or ninth rib, and continues to the last interspace, where it ends. In its course, as it crosses each interspace, it gives off anterior intercostal branches which anastomose, as in the upper interspaces, with the aortic intercostal arteries. Branches are also given off to supply the pericardium, the diaphragm, and the abdominal muscles.

Arteria thoracica interna

Artère thoracique interne