The aortic bifurcation gives rise to the two common iliac arteries, which incline down- wards and laterally on the medial aspects of psoas major (Fig. 4.90). The vessels terminate in front of the sacroiliac joints by dividing into internal and external iliac arteries. The right common iliac artery crosses in front of the left common iliac vein, while that on the left is crossed by the inferior mesenteric vessels. The ureter crosses either the lower end of the common iliac artery or the commencement of its external branch (Fig. 4.90). The internal iliac artery begins at the bifurcation of the common iliac artery and descends on the lateral wall of the pelvis (p. 238).
The external iliac artery curves round the pelvic brim (Fig. 4.90) and, passing behind the inguinal ligament, enters the thigh as the femoral artery (Fig. 6.19). The external iliac artery is accompanied on its medial side by the corresponding vein and posterolaterally by psoas major. The external iliac vessels are crossed by the ovarian vessels in the female and by the ductus deferens in the male. Near the inguinal ligament the artery gives off the inferior epigastric artery, which runs upwards and medially, medial to the deep inguinal ring (Figs 4.18 & 4.23).
Each external iliac vein begins behind the inguinal ligament as the continuation of the femoral vein (Fig. 4.90). It receives the inferior epigastric vein, ascends on the medial side of the corresponding artery and joins the internal iliac vein (p. 145) to form the common iliac vein. The two common iliac veins continue upwards and medially, passing behind the right common iliac artery, by which they may be com- pressed, before uniting to form the inferior vena cava.