The hip bone is a large irregularly shaped flat bone. It is also referred to as innominate bone. Along with the sacrum, the two hip bones come together to form a pelvic girdle. Each of the hip bones consists of three embryonic elements. They are ilium, ischium and pubis which come together at a Y-shaped junction. These elements fuse with age but before the fusion, the elements are separated from each other by cartilage. The ilum is the upper elements and is a wide flat rectangular plate. The border of the plate has an iliac crest which is thick. It is mainly present for the muscles to be attached to the abdominal wall.