The correct answer is sacrum; greater trochanter of the femur.
The piriformis is a muscle in the gluteal region of the lower limb. The muscle originates from the front part of the sacrum, which is the triangular bone at the base of the spine found in the gluteal region.
The muscle inserts on the greater trochanter of the femur, which is a powerful protuberance of the femur and a very important part of the skeletal system. The femur is the thigh bone, considered the longest and strongest bone in the human body.