The bones of the body in the approximate center of the hip are the sit bones of the human pelvis structure. The sciatic bone is a relatively low horizontal bone in the pelvic bone. When the human body maintains a sitting posture, the sit bones are in direct contact with the plane, thus supporting the weight of the human body. And the middle position above the buttocks on both sides is the human tailbone, the tailbone is the most end of the human spine bones, the shape is similar to the tail of other mammals, so it is also called the tailbone. The tailbone forms an equilateral triangle with the two sitting bones of the buttocks, and directly above the two sides of the buttocks is the iliac bone in the pelvic structure of the human body. The ilium is on the back side of the body, and the two sides of the ilium are connected to the sacrum, forming the sacroiliac joint on both sides. Below the ilium is the sit bones, and in front of the ilium is the pubic bone.