Buttocks

In many cultures, the buttocks play a role in sexual attraction. Many cultures have also used the buttocks as a primary target for corporal punishment, as the buttocks' layer of subcutaneous fat offers protection against injury while still allowing for the infliction of pain.

Structure

The buttocks are formed by the masses of the gluteal muscles or "glutes" (the gluteus maximus muscle and the gluteus medius muscle) superimposed by a layer of fat. The superior aspect of the buttock ends at the iliac crest, and the lower aspect is outlined by the horizontal gluteal crease. The gluteus maximus has two insertion points: 1⁄3 superior portion of the linea aspera of the femur, and the superior portion of the iliotibial tractus. The masses of the gluteus maximus muscle are separated by an intermediate intergluteal cleft or "crack" in which the anus is situated.

The analogous anatomical structures known as ischial callosities allow primates to sit upright without resting their weight on their feet as four-legged animals do. The pads enable the primates to sleep sitting upright on thin branches, beyond reach of predators, without falling. Humans do not possess ischial callosities due to the gluteal muscles being large enough to provide the same cushioning. Females of certain species of baboon have red callosities that blush to attract males. In the case of humans, females tend to have proportionally wider and thicker buttocks due to higher subcutaneous fat and proportionally wider hips. In humans they also have a role in propelling the body in a forward motion and aiding bowel movement.

Some baboons and all gibbons, though otherwise fur-covered, have characteristic naked ischial callosities on their rears. While human children generally have smooth buttocks, mature males and females have varying degrees of hair growth, as on other parts of their body. Females may have hair growth in the gluteal cleft (including around the anus), sometimes extending laterally onto the lower aspect of the cheeks. Males may have hair growth over some or all of the buttocks.