The pharyngeal arch arteries (PAAs) form during the third to fifth weeks of development when mesoderm-derived angiogenic mesenchymal cells migrate from the pharyngeal arches toward the aortic sac to form the endothelial lining of the developing vessels. The six paired branches emerge in a cranial to caudal sequence and terminate in the dorsal aortae. Neural crest cells within the pharyngeal arches give rise to the vascular smooth muscle cells and pericytes that contribute to the outer layer of the developing vasculature. The proximal portion of the common carotid artery (CCA) arises from the ventral aortic root connecting the third and fourth PAA while the homologous structure of the dorsal aorta regresses. As this ventral root elongates, the third PAA remains attached and ultimately forms the proximal portion of the internal carotid artery (ICA). The distal portion of the ICA is formed by the cranial segment of the dorsal aortae. The external carotid artery (ECA) then develops de novo as a branch of the CCA via angiogenesis (Frisdal and Trainor 2014).