False-colour anteroposterior X-ray of a normal adult, female pelvis. The pelvis is formed by the sacrum, coccyx, and two innominate (hip) bones. Here, the sacrum is at top centre, articulating with each innominate bone at the sacro-iliac joints. Left and right hip bones meet at the symphysis pubis (bottom). Also visible is the articulation of the rounded head of each femur (thigh bone) with each hip socket. The pelvis supports and protects internal organs & tissues, and provides site for attachments of the muscles of the trunk & lower limbs. Mechanically, its most important role is to transmit the weight of the upper body to the ground.