The pelvis provides a location for the large muscles of the lower body to connect, giving humans the ability to walk, run, sit and kneel. It also surrounds the reproductive organs, bladder and rectum, forming a cavity in which these organs can be supported and protected.
The three primary bones of the pelvis include the hip bones, sacrum and coccyx. In young children, each hip bone begins as three separate bones, and these bones fuse as a person ages. The top of the hip bone is called the ilium and is what people generally think of as the hip. This ilium curves downward to the area known as the ischium, which connects to the femur. Each of the hip bones curve toward the front of the body to a bony area known as the pubis. A joint exists between the pubic bones that can expand in females during childbirth, allowing the baby's head to pass safely through the birth canal.
The back of the pelvis ends with the sacrum and coccyx. The sacrum extends downward from the vertebrae. It is composed of five fused vertebrae. The coccyx attaches directly below the sacrum and is composed of four fused vertebrae. The muscles of the pelvic floor are attached to the coccyx.