At the level of lumbar vertebra L4, the aorta gives rise to the common iliac arteries, which then divide into internal and external iliac arteries. The internal iliac artery is the artery whose seven branches provide blood primarily to pelvic viscera (organs) and the pelvic wall. In descending order, these begin with the iliolumbar and lateral sacral arteries that connect to the pelvic wall, followed by the middle rectal artery, which supplies the rectum. Next, the superior and inferior vesical arteries deliver blood to the urinary bladder and in males the prostate and seminal vesicles. The vaginal and uterine arteries supply the vagina and uterus, respectively. The superior and inferior gluteal arteries carry blood to gluteal muscles, and the obturator artery to the medial thigh's adductor muscles. Finally, the internal pudendal artery supplies the perineum and external genitals, including blood that engorges genitals during sexual arousal.Blood return from the pelvis begins with the right and left internal iliac veins. These drain the urinary bladder, rectum, external genitals, prostate and ductus deferens in males, uterus and vagina in females, pelvic wall, medial thigh, and hip. The internal iliac veins join the external iliacs to form the paired common iliac veins. These in turn meet to become the inferior vena cava, which carries blood back to the heart's right atrium. Blood supplying the testes and ovaries drains as part of abdominal circulation, emptying from paired gonadal veins directly into the inferior vena cava.