Hip bone Hip bone The hip bone (os coxa, innominate bone, pelvic bone or coxal bone) is a large flat bone, constricted in the center and expanded above and below. In some vertebrates (including humans before puberty) it is composed of three parts: the ilium, ischium, and the pubis. The two hip bones join at the pubic symphysis and together with the sacrum and coccyx (the pelvic part of the spine) comprise the skeletal component of the pelvis – the pelvic girdle which surrounds the pelvic cavity. They are connected to the sacrum, which is part of the axial skeleton, at the
Sacrum κλόνις (Latinized "clonis"); this term is cognate to Latin "clunis" "buttock", Sanskrit "" "haunch" and Lithuanian "šlaunis" "hip, thigh". The Latin word is found in the alternative Latin name of the sacrum, "ossa clunium", as it were "bones of the buttocks". Due to the fact that the os sacrum is broad and thick at its upper end, the sacrum is alternatively called "os latum", "broad bone". In dogs the sacrum is formed by three fused vertebrae. The sacrum in the horse is made up of five fused vertebrae. In birds the sacral vertebrae are fused with the lumbar and some