<P> 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 . </P> <P> 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 sacroiliac joint . Each hip bone is connected to the corresponding femur (thigh bone) (forming the primary connection between the bones of the lower limb and the axial skeleton) through the large ball and socket joint of the hip . </P> <P> The hip bone is formed by three parts: ilium, ischium, and pubis . At birth, these three components are separated by hyaline cartilage . They join each other in a Y - shaped portion of cartilage in the acetabulum . By the end of puberty the three regions will have fused together, and by the age of 25 they will have ossified . The two hip bones join each other at the pubic symphysis . Together with the sacrum and coccyx, the hip bones form the pelvis . </P> <P> Ilium (plural ilia) is the uppermost and largest region . It makes up two fifths of the acetabulum . It is divisible into two parts: the body and the ala or wing of ilium; the separation is indicated on the top surface by a curved line, the arcuate line, and on the external surface by the margin of the acetabulum . The body of ilium forms the sacroiliac joint with the sacrum . The edge of the wing of ilium forms the S - shaped iliac crest which is easily located through the skin . The iliac crest shows clear marks of the attachment of the three abdominal wall muscles . </P>

Where do the ilium the ischium and the pubis meet