The vasculature begins to form during the third week of human embryo development, around day 18, when mesenchymal cells differentiate into angioblasts. These angioblasts cluster together, flatten, and fuse with other clusters to begin forming primitive endothelium-lined channels. The endothelium then differentiates to form distinct layers while new vessels begin to develop by budding from a preexisting vessel. During the fourth week, the umbilical arteries anastomose with the dorsal intersegmental arteries to form an umbilical artery, precursor of the common and internal iliac arteries. During the fifth week, the external iliac and sciatic arteries arise from the same umbilical artery root and interconnect, the sciatic arteries being destined eventually to regress. By the third month of development, the external iliac artery forms the major blood supply to the lower extremities through its branches, including the deep circumflex iliac artery and its continuation as the femoral artery (Hammond et al. 2021; Greebe 1977; Tamisier et al. 1990; Senior 1919; Evans 1909).