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
Body of sphenoid bone the crest is an irregular opening leading into the corresponding sphenoidal air sinus. These sinuses are two large, irregular cavities hollowed out of the interior of the body of the bone, and separated from one another by a bony septum, which is commonly bent to one or the other side. They vary considerably in form and size, are seldom symmetrical, and are often partially subdivided by irregular bony laminae. Occasionally, they extend into the basilar part of the occipital bone nearly as far as the foramen magnum. They begin to be developed before birth, and are of a considerable size