The great vessels begin to form during the third week of embryo development, deriving from both mesoderm and ectoderm. The pharyngeal mesoderm comes from mesodermal cells, while the neural crest cells originate from the ectoderm layer. Aortic arches develop from the distal-most portion of the truncus arteriosus, the aortic sac (Sadler and Langman 2010). The aortic sac and the two dorsal aortae meet at the aortic arches. The aortic arches make up six pairs of arteries and line the pharyngeal arches within the pharyngeal wall. Branches of each pharyngeal arch wrap around the primitive pharynx and terminate in the dorsal aorta.