Figure 5.

Embryologic development of a normal left aortic arch and single bilateral VAs. (a) Dorsal and ventral primitive aorta. Seven intersegmental arteries branch off the dorsal aorta and are linked by longitudinal plexiform anastomosis. (b) Involution of the first through sixth intersegmental arteries bilaterally. The dorsal branch of the seventh intersegment artery forms the V1 segment of the VA. The dorsal aortae fuse to form the descending aorta (Des Ao). (c) The VA extends cranially, and unites with the contralateral counterpart to form the basilar artery (BA). A: aorta; R Dor Ao: right dorsal aorta; L Dor Ao: left dorsal aorta; CCA: common carotid artery; Des Ao: descending aorta; PA: pulmonary artery; SA: segmental artery; VA: vertebral artery. (Adapted from Polguj et al.).