 The sacral plexus lies on the back of the pelvis in front of the piriformis muscle and the pelvic fascia.In front of it are the internal iliac artery, internal iliac vein, the ureter, and the sigmoid colon.The superior gluteal artery and vein run between the lumbosacral trunk and the first sacral nerve, and the inferior gluteal artery and vein between the second and third sacral nerves.