The human gluteal region is defined by twin hemispherical masses that are located between the lower back, or lumbar region, and the perineum. These dome-shaped structures consist mainly of adipose tissue, or fat, and three sets of underlying muscle tissue. Nearly the entire region is made of soft tissue, as the underlying bone of the pelvis does not follow the characteristic bulging shape of the buttocks.
The outermost layer of the buttocks is skin. The skin of this area is substantially similar to skin found elsewhere on the body and can be smooth or hairy. Under the skin is a thick layer of fat that serves as a cushion while sitting and gives the buttocks much of their definition.
Under the layer of fat lie three groups of muscles. The gluteus maximus is the largest and outermost muscle in each buttock. At its superior edge, the gluteus maximus attaches to the iliac crest and runs downward and out toward the flank, giving the hip much of its definition. Interior to the gluteus maximus is the gluteus medius, which also attaches to the ilium but runs a shorter distance outward than the maximus muscle. Interior to these, and the smallest of the three, is the gluteus minimus, which acts to abduct the thigh and stabilize the hip. These structures are fed by the superior and inferior gluteal arteries, and they are enervated by the gluteal and cluneal nerves.