The internal thoracic artery (internal mammary artery) is a long, paired blood vessel located in anterior part of thorax, near and alongside of the sternum. It springs from the lower side of subclavian artery, just at the level of origin of the vertebral artery, which arises from its upper surface and runs upwards. Then the internal thoracic artery travels downwards, passing by and behind the clavicle and subclavian vein.
The internal thoracic enters the cavity of the thorax through an inlet known as superior thoracic aperture. Then it descends vertically, running behind the ribs and parallel to the border of the sternum, on the posterior surface of the first to seventh costal cartilages. It is covered, there, by the transversus thoracis muscle and the parietal pleura. As it descends, it gives off the anterior intercostal branches (supply intercostal muscles and cartilages), the pericardiophrenic artery (supplies pericardium), and the perforating branches, which supply the subcutaneous tissue and overlying skin.
At the end of its long, and almost straight course, the internal thoracic divides into the musculophrenic artery and the superior epigastric artery. The muscolophrenic stretches along the costal arch on the line of attachment of the costal part of diaphragm to the thorax, supplying the diaphragm and the intercostal muscles. Meanwhile, the superior epigastric artery runs downwards and pierces the wall of the sheath of the rectus abdominis muscle to anastomose with the inferior epigastric artery, which originates from the external iliac artery.
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| Anterior view of thorax showing the internal thoracic artery and its branches. |