Fig. 1

Development of the aorta and branch vessels. a Illustration showing the schematic development of the aorta and arch branch vessels from six pairs of aortic arches. Please note that the six arches are never seen together in the foetus, since they develop and regress in a craniocaudal direction. Also, the fifth arch is not present in most foetuses. b Illustration showing the fully developed normal left aortic arch and branch vessels, with corresponding colour codes. a The left arch between the left common carotid and left subclavian (red) is derived from the left fourth arch (red). The ventral aorta (purple) forms the ascending aorta and the right brachiocephalic trunk while the dorsal aorta (green) forms the descending thoracic aorta. The left subclavian artery is derived from the left seventh intersegmental artery (brown), while the right subclavian artery is derived proximally from the right fourth arch (red), in the mid portion from the right dorsal aorta (green) and the distal portion from the right seventh intersegmental artery (brown). The aortic root and main pulmonary artery are derived from division of the truncus arteriosus (pink). The ductus arteriosus (blue) is formed from the dorsal portion of the left sixth arch, while the right and left pulmonary arteries are derived from ventral portions of the right and left sixth arches (yellow) respectively. Common carotid arteries are derived from the third arches (orange), while internal carotid arteries are formed from the third arches (orange) and the dorsal aorta (green). External carotid arteries are derived from the third arch branches (black)