The pelvis has four bones, which are the hip bones on both sides, the sacrum on one side and the coccyx on the other side. The hip bones on both sides form the pubic symphysis by borrowing the pubic ligament on the front side, the sacroiliac joint on both sides and the sacrum on the back side, and the sacrum and the coccyx form the sacrococcygeal joint, and these four bones form the pelvis. In addition, the hip bones on both sides are formed by the three bones of the ilium, the sit bones and the pubic bone respectively. In addition, there are several important ligaments in the pelvis, including the sacral nodal ligament between the sacrum and coccyx and the sciatic tuberosity, and also the sacrospinous ligament between the sacrum and coccyx and the sciatic spine.