The buttocks do not contain bones. Instead, this area is primarily composed of soft tissues that provide its shape and function. The bones are found beneath and around these soft tissues, forming the underlying skeletal framework.
Skeletal Foundation of the Region
The foundational structure beneath the buttocks is the pelvis, a basin-shaped bony ring that connects the spine to the lower limbs. This structure consists of several bones, including the two hip bones, the sacrum, and the coccyx. Each hip bone is formed by the fusion of three separate bones: the ilium, ischium, and pubis. The ilium is the large, flaring upper part, the ischium is the lower, posterior portion often referred to as the “sit bone,” and the pubis is the front part.
The sacrum is a triangular bone at the base of the spine, formed from five fused vertebrae, located between the two hip bones. Below the sacrum is the coccyx, commonly known as the tailbone, which is a small bone at the very end of the spine. These bones provide attachment points for muscles and ligaments.
Composition of the Buttocks
The buttocks are primarily made up of muscles, fat, and connective tissue. The most prominent components are the gluteal muscles, which include the gluteus maximus, gluteus medius, and gluteus minimus. The gluteus maximus is the largest and most superficial of these muscles, largely responsible for the rounded contour of the buttocks. The gluteus medius lies beneath the maximus, and the gluteus minimus is the smallest and deepest of the three.
Adipose tissue, or fat, also contributes to the shape and cushioning of the buttocks. This fat layer, along with connective tissues, encases the muscles and helps define the overall form. These soft tissues provide padding and allow for flexibility and movement in the hip region.
Role of the Buttocks and Pelvic Bones
The gluteal muscles and underlying pelvic bones serve several functions. The gluteal muscles enable hip joint movement, including extending the thigh backward, moving it away from the body (abduction), and rotating it. These movements support everyday activities like standing up, walking, running, and climbing stairs.
The pelvic bones provide a stable base for the torso and connect it to the legs. They support the body’s weight, especially when sitting, with the ischium bones acting as the primary weight-bearing points. The soft tissues of the buttocks provide cushioning, protecting the pelvic bones and underlying organs from impact during activities such as sitting or falling. The muscles also stabilize the pelvis, particularly during single-leg stance, important for walking.