The time lag in the development of bronchial arteries

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Abstract
Reconstruction of the pulmonary and aortic trunks, together with adjacent structures in a 41 mm human embryo of the Carnegie Collection, demonstrates that as late as the ninth week after ovulation the bronchial artery is still a tiny vessel, arising ventrolaterally from the descending aorta at the level of the third pair of dorsal aortic‐intercostal arteries, and that any extension of it along the bronchial tree must still be of capillary calibre since no visible branches can be followed into the root of the lung. In sum, bronchial arteries arise later, more slowly and from a lower position than has hitherto been assumed. By contrast, the anomalous systemic pulmonary artery that supplies the right posterior basal bronchopulmonary segment in this fetus and which now arises from the aorta just above the celiac artery, is a robust vessel. Such systemic pulmonary arteries must arise very early, at the level of the definitive pulmonary arteries, and keep pace with them in growth, whether or not their stems descend along the aorta with the migrating celiac artery.