Development of the coronary arteries in staged human embryos (the Paris Embryological Collection revisited).

Twenty seven human embryos from stages 15 to 23 (postsomitic period), belonging to the collection of the "UFR Biomédicale des Saints-Pères, Université René Descartes Paris V", were studied. Details of the aorticopulmonary cleavage were analysed specially aortic valve development and origin of the coronary artery. At stage 18 the aortic valve was clearly distinguished (cup-shaped) presenting semilunar valves and aortic sinus (Valsalvae); at this stage the left coronary artery was detected in 66.7 per cent of the cases as an endothelial epicardial invagination. At stage 19, the left and right coronary arteries were detected simultaneously in 100 per cent of the cases. At stage 20, the coronary arteries showed greater structural complexity with a coat of mesenchymal cells. These results agree with previous data from different embryological collections. These findings suggest that the left coronary artery has a tendency to develop earlier than the right. We found no evidence of the coronary origin from the aortic lumen. This work provides additional information about the embryological development of the heart, obtained from the analyses of a French collection of human embryos.