Vessels begin to appear in the splanchnic mesoderm of the embryo around gestational day 18 (Streeter 1919). As the embryo grows, small branches appear at fairly regular intervals around the primitive aorta (DeSesso 2017). Around the 28th day of gestation, the hind limb buds appear and mark the formation of the intersegmental arteries, which later form the common iliac and external iliac arteries as the first vessels to penetrate the nascent hind limb buds (DeSesso 2012). Primarily, the dorsal intersegmental arteries coalesce with the ventral segmental arteries to form a single central artery, the common iliac artery (CIA) (DeSesso 2017). The CIA serves as the stem for the external iliac and the umbilical artery (presumptively the internal iliac artery) (DeSesso 2017). When the embryo is less than 1.5 mm long, the umbilical artery arises at about the level where the fourth cervical mesodermal somite and its portion ventral to the external iliac artery come together to form the origin of the internal iliac artery (Sakthivelavan et al. 2010; DeSesso 2017). The internal iliac artery (IIA) is the major artery of the pelvis. It divides into anterior and posterior divisions, the internal pudendal artery (Figs. 64.1, 64.2, and 64.3) (IPA) being one of the parietal branches of the anterior division (Sakthivelavan et al. 2010). However, given the variability of fetal branching patterns, four types of arrangements of branches of the fetal IIA have been distinguished (Pielson et al. 1930). The IPA is one of the three largest branches, along with the superior and inferior gluteal arteries, used for classification into types. Type 1 is defined as the IPA and inferior gluteal artery arising from the anterior trunk of the IIA (Sakthivelavan et al. 2010). In Types 2 and 4, the three arteries arise independently from the IIA, or from a common stem, respectively. In Type 3, the IPA remains distinct while the superior and inferior gluteal arteries arise from the common trunk (Sakthivelavan et al. 2010).