The term “buttocks,” often called the “butt,” refers to the prominent rounded area at the posterior of the human trunk. While its general location is understood, the precise anatomical boundaries and structures defining this region are more specific than common perception suggests. Understanding these landmarks provides a clearer picture of where the gluteal region truly begins and ends.
The Gluteal Region’s Upper Border
The superior boundary of the gluteal region is defined by bony landmarks. Laterally, this upper limit is marked by the iliac crest, which is the curved upper border of the hip bone. This palpable ridge forms a demarcation across the posterior pelvis.
Medially, the upper part of the gluteal region encompasses the sacrum and coccyx, which are bones at the base of the spine. The intergluteal cleft, also known as the natal cleft or buttock crease, is a deep vertical furrow situated between the two gluteal regions. This cleft begins around the level of the third or fourth sacral vertebra and extends downwards, with the sacrum and coccyx forming the bony foundation beneath its upper portion. These bony structures and overlying soft tissues create the upper contour of the buttocks.
Anatomy and Extent of the Buttocks
Beyond its upper border, the buttocks are shaped by muscles and adipose tissue. The gluteal muscles, including the gluteus maximus, gluteus medius, and gluteus minimus, are the primary muscle group defining the buttocks. The gluteus maximus is the largest and most superficial of these muscles, contributing to the overall shape and prominence of the buttocks. It originates from the ilium, sacrum, and coccyx, inserting on the femur and iliotibial tract, and plays a role in hip extension and external rotation.
Beneath the gluteus maximus lies the gluteus medius, a broad, fan-shaped muscle originating from the outer surface of the ilium. The gluteus minimus, the smallest of the three, is situated even deeper, directly under the gluteus medius. Both the gluteus medius and minimus contribute to hip abduction and stabilization of the pelvis during movement, such as walking. These muscles, along with smaller deep lateral rotators, provide the underlying structure and function of the region.
The contour and rounded appearance of the buttocks are also influenced by the distribution and volume of subcutaneous adipose tissue, commonly known as fat. This fat content varies among individuals, contributing to the unique shape and projection. The inferior boundary of the buttocks is marked by the gluteal fold, a horizontal skin crease that separates the buttocks from the posterior upper thigh. This fold is formed by the fibrous attachments of the skin to the deep fascia, rather than being solely the lower edge of the gluteus maximus muscle.