The lungs receive blood from two sets of arteries. The pulmonary arteries follow the bronchi and ramify into capillary networks that surround the alveoli, allowing exchange of oxygen and carbon dioxide. The bronchial arteries derive from the aorta. They supply oxygenated blood to the tissues of the lung that are not in close proximity to inspired air, such as the muscular walls of the larger pulmonary vessels and airways (to the level of the respiratory bronchioles) and the visceral pleurae. The origin of the right bronchial artery is quite variable. It arises frequently from the third right posterior intercostal artery (the ﬁrst right aortic intercostal artery) and descends to reach the posterior aspects of the right main bronchus. It may arise from a common stem with the left inferior bronchial artery, which origi- nates from the descending aorta slightly inferior to the point where the left main bronchus crosses it. Or it may arise from the inferior aspect of the arch of the aorta and course behind the trachea to reach the posterior wall of the right main bronchus.