The buttocks (: buttock) are two rounded portions of the exterior anatomy of most

mammals A mammal () is a vertebrate animal of the class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three middle e ...

, located on the posterior of the pelvic region. In humans, the buttocks are located between the lower back and the

perineum The perineum (: perineums or perinea) in placentalia, placental mammals is the space between the anus and the genitals. The human perineum is between the anus and scrotum in the male or between the anus and vulva in the female. The perineum is ...

. They are composed of a layer of exterior skin and underlying subcutaneous fat superimposed on a left and right

gluteus maximus The gluteus maximus is the main extensor muscle of the hip in humans. It is the largest and outermost of the three gluteal muscles and makes up a large part of the shape and appearance of each side of the hips. It is the single largest muscle in ...

and

gluteus medius muscle The gluteus medius, one of the three gluteal muscles, is a broad, thick, radiating muscle. It is situated on the outer surface of the pelvis. Its posterior third is covered by the gluteus maximus, its anterior two-thirds by the gluteal aponeuros ...

s. The two gluteus maximus muscles are the largest muscles in the human body. They are responsible for movements such as straightening the body into the upright (standing) posture when it is bent at the waist; maintaining the body in the upright posture by keeping the hip joints extended; and propelling the body forward via further leg (hip) extension when walking or running. In many cultures, the buttocks play a role in

sexual attraction Sexual attraction is attraction on the basis of sexual desire or the quality of arousing such interest. Sexual attractiveness or sex appeal is an individual's ability to attract other people sexually, and is a factor in sexual selection or m ...

. Many cultures have also used the buttocks as a primary target for

corporal punishment A corporal punishment or a physical punishment is a punishment which is intended to cause physical pain to a person. When it is inflicted on Minor (law), minors, especially in home and school settings, its methods may include spanking or Padd ...

, 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 The gluteus maximus is the main extensor muscle of the hip in humans. It is the largest and outermost of the three gluteal muscles and makes up a large part of the shape and appearance of each side of the hips. It is the single largest muscle i ...

and the

) superimposed by a layer of

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers specif ...

. The superior aspect of the buttock ends at the

iliac crest The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superolateral margin of the greater pelvis. Structure The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posterio ...

, and the lower aspect is outlined by the

horizontal gluteal crease The gluteal sulcus (also known as the gluteal fold, tuck, fold of the buttock, horizontal gluteal crease, or gluteal furrow) is an area of the body of humans and anthropoid apes, described by a horizontal crease formed by the inferior aspect of t ...

. The gluteus maximus has two insertion points: superior portion of the

linea aspera The linea aspera () is a ridge of roughened surface on the posterior surface of the shaft of the femur. It is the site of attachments of muscles and the intermuscular septum. Its margins diverge above and below. The linea aspera is a prominent ...

of the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

, and the superior portion of the iliotibial tractus. The masses of the gluteus maximus muscle are separated by an intermediate

intergluteal cleft The intergluteal cleft or just gluteal cleft, also known by a number of synonyms, including natal cleft and cluneal cleft, is the groove between the buttocks that runs from just below the sacrum to the perineum, so named because it forms the vis ...

or "crack" in which the

anus In mammals, invertebrates and most fish, the anus (: anuses or ani; from Latin, 'ring' or 'circle') is the external body orifice at the ''exit'' end of the digestive tract (bowel), i.e. the opposite end from the mouth. Its function is to facil ...

is situated. The buttocks allow primates to sit upright without resting their weight on their feet as four-legged animals do. Females of certain species of

baboon Baboons are primates comprising the biology, genus ''Papio'', one of the 23 genera of Old World monkeys, in the family Cercopithecidae. There are six species of baboon: the hamadryas baboon, the Guinea baboon, the olive baboon, the yellow ba ...

have red buttocks that blush to attract males. In the case of humans, females tend to have proportionally wider and thicker buttocks due to higher

subcutaneous fat The subcutaneous tissue (), also called the hypodermis, hypoderm (), subcutis, or superficial fascia, is the lowermost layer of the integumentary system in vertebrates. The types of cells found in the layer are fibroblasts, adipose cells, and ...

and proportionally wider

hip In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint on t ...

s. In humans they also have a role in propelling the body in a forward motion and aiding bowel movement. Some baboons and all

gibbon Gibbons () are apes in the family Hylobatidae (). The family historically contained one genus, but now is split into four extant genera and 20 species. Gibbons live in subtropical and tropical forests from eastern Bangladesh and Northeast Indi ...

s, though otherwise

fur A fur is a soft, thick growth of hair that covers the skin of almost all mammals. It consists of a combination of oily guard hair on top and thick underfur beneath. The guard hair keeps moisture from reaching the skin; the underfur acts as an ...

-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 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.

Names

The

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

name for the buttocks is (English pronunciation , classical pronunciation ''nătes'' A New Dictionary of the Latin and English Languages, published Ward, Lock & Co., London, 1908) which is plural; the singular, (buttock), is rarely used. There are many colloquial terms for them.

References

External links

"The Muscles and Fasciæ of the Thigh"
(by Henry Gray) a
"Anatomy of the Human Body"
1918. {{Authority control Human surface anatomy Lower limb anatomy Human sexuality

Structure

Names

See also

References

External links