The Descending Aorta is the continuation of the aortic arch. Superiorly it lies to the left of the midline, and inferiorly it leaves the posterior mediastinum as a midline structure passing behind the crura of the diaphragm. It gives rise to the third through the eleventh posterior Intercostal arteries that arch upward to the lower nine intercostal spaces. It gives rise to the bronchial and esophageal arteries. Usually there are two bronchial arteries on the left and one on the right. A second bronchial artery on the right is common; when present it arises from the first aortic intercostal artery (third posterior intercostal).