This chapter provides evolutionary theoretical background for variations and defects of lower limb muscles; and summarizes each variation and defect found in every skeletal muscle. Gluteus maximus originates from the ilium, sacrum, coccyx, aponeurosis of erector spinae, sacrotuberous ligament, and the gluteal aponeurosis. Gluteus maximus has similar origins and attachments in the apes, but compared with humans, gluteus maximus in the apes is reduced in size and thickness and is more developed in its distal portions. Variations in the gluteal muscles including division of the muscle into multiple parts should be acknowledged when considering injections into the gluteal musculature. Piriformis may have an origin from the upper part of the pelvic aspect of the sacrotuberous ligament. Anomalous presentations of piriformis include variable insertions, the presence of accessory slips, complete absence, or splitting of the muscle belly by the peroneal portion of the sciatic nerve.