The pelvis is a group of fused bones and may be considered the first step in the linkage of the axial skeleton (bones of the head, neck, and vertebrae) to the lower appendages. The part of the axial skeleton directly communicating with the pelvis is the lumbar spinal column. The femur is the appendicular skeletal bone connected to the pelvis at the acetabulum, a bony ring formed by the fusion of three bones: the ilium, ischium, and pubis. The main function of the pelvis is support for locomotion, as it provides attachment points for muscles, tendons, and ligaments. While stiff joints bind the axial skeleton to the pelvis, the appendicular skeleton is joined via a relatively free-floating ball and socket joint between the femur and the acetabulum to allow maximal mobility of the joint.

In discussing the pelvis, a distinction can be made between the “pelvic spine” and the “pelvic girdle.” The pelvic girdle, also known as the os coxae, Latin for “bone of the hip,” consists of the fused bones identified individually as the ilium, ischium, and pubis. The ring of this girdle is closed in the anterior by the pubic symphysis between the left and right pubic bones, and in the posterior between the left and right ilia and the sacrum at the sacroiliac joints. The pelvic spine consists of the sacrum and coccyx. Together these two parts form the bony pelvis.