The vascular system starts to develop during the fourth to fifth week of gestation, when six pairs of primitive pharyngeal arch arteries form. The fourth right pharyngeal arch generates the proximal part of the right subclavian artery, while the seventh intersegmental artery forms its distal part. The fourth left pharyngeal arch contributes to the entire left subclavian artery. The seventh intersegmental artery, derived from the dorsal aorta, contributes to the formation of the axial arteries bilaterally, which then contribute to the subclavian artery. Owing to its complex development, the axillary artery can have various origins. A few of the named vessels can arise as common trunks, or their branches can branch separately from the axillary artery. The embryological variants of the axillary artery and subsequently the thoracodorsal artery become significant as these vessels have implications for reconstructive surgery that will be explored later in this chapter (Kumar et al. 2018).