On the development of the coronary arteries in human embryos, stages 14-19.

Each coronary artery in humans develops, initially, from two anlagen, one distal and the other proximal. The distal anlage, which is forerunner of the subepicardial branches of the coronary arteries, develops as subepicardial vascular networks on the atrioventricular and interventricular sulci and on the walls of the ventricles and bulbus; these networks are the right-posterior and left-anterior ones. The proximal anlage, which is forerunner of the truncus of the right and left coronary arteries, develops as several endothelial buds of the truncus arteriosus. Normally, only two buds, right and left, hollow out, increase in length and connect with the right and the left vascular networks, respectively, so that the coronary arteries are formed. The cardiac veins appear together with the coronary arteries, but as independent vessels. The authors advance a number of hypotheses as to the origin of certain variations and malformations of the coronary arteries.