The buttocks (singular: buttock) are rounded portions of the anatomy located on the posterior of the pelvic region of the apes, including humans and many other bipeds or quadrupeds.

Anatomy

The buttocks are formed by the masses of the gluteal muscles or 'glutes' (the gluteus maximus and the gluteus medius) 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 gluteal cleft or "crack" in which the anus is situated.

The buttocks allow primates to sit upright without needing to rest their weight on their feet as four-legged animals do. Females of certain species of baboon have red buttocks that "blush" to attract males. In the case of humans, females tend to have wider and thicker buttocks due to higher subcutaneous fat and wider hips.

Some baboons and all gibbons, though otherwise fur-covered, have characteristic naked callosities on their buttocks. 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 generally have hair growth in the gluteal cleft (particularly around the anus), often extending laterally onto the lower aspect of the cheeks. In addition to such areas, males often have hair growth over the most of (or the entire) the buttocks.

Connotations

The English word of Greek origin "callipygian" indicates someone who has beautiful buttocks. However, the qualities that make buttocks "beautiful" or "well-formed" are not fixed, as sexual aesthetics of the buttocks vary considerably from culture to culture, from one period of fashion to another and even from person to person.

In ancient astrology, various parts of the body were associated with signs of the zodiac - e.g. the buttocks to the Balance. Depending on the context, exposure of the buttocks in non-intimate situations often causes feelings of shame, embarrassment or humiliation in a non-exhibitionist subject, and embarrassment or amusement in a non-voyeurist audience (see "pantsing"). Expressions such as being "caught with one's pants/ trousers down" or more explicitly in Dutch, "met de billen bloot" ("with bared buttocks"), use the image as a metaphor for non-physical embarrassment as well.

Willfully exposing one's own bare buttocks as a protest, a provocation, or just for fun (especially but not exclusively practiced by youngsters such as North American frat boys) is called "mooning".