The three bones of the os coxa, or hip bone, are the ilium, ischium and pubis, according to Dartmouth College. By adulthood, these three bones have grown together to form a single bone. When combined with the sacrum, these bones make up the bony pelvis.
The ilium forms the fan-shaped portion of the pelvis, according to the University of Arkansas. The crest, or top part, is attached to abdominal wall muscles. Ligaments are also connected to parts of the ilium. The ischium is located at the lower back portion of the hip bone and is joined to ligaments. The pubis forms the lower front portion of the pelvis. This bone attaches to the root of the penis.