What is the physiological structure of ass! ?

The shape of the buttocks leans backward, with the iliac crest on the upper edge and the gluteal groove on the lower edge. When the human body is upright, the whole hip is square, and the hip pits on both sides are obvious. There are differences in hip shape between men and women. Women's buttocks are rich and smooth, and the angle between the posterior superior iliac crest is 90o. Male hips are small, square, angular and more obvious. The intersection angle of the posterior superior iliac crest is 60o.

The skin of buttocks is thick, and sebaceous glands and sweat glands are abundant. The superficial fascia is well developed, and there are many fiber bundles connecting the skin and the deep fascia, filling the thick subcutaneous fat of the buttocks, and the lower part is thick and dense, forming a fat pad, which bears the pressure when sitting. The cutaneous nerves of buttocks can be divided into three groups. The gluteal epithelial nerve is the lateral branch of the posterior branch of the 1 ~ 3 lumbar nerve, which passes through the outer edge of erector spinae, the bone fiber duct of thoracolumbar fascia, and the iliac crest, and is distributed in the upper buttock skin. When the waist is sprained, the fixed gluteal muscle epithelial nerve is easily dislocated by pulling, causing low back and leg pain. The middle gluteal nerve is the posterior branch of 1 ~ 3 sacral nerve, which passes through the deep fascia in the middle of the line from the posterior superior iliac spine to the tip of coccyx, and is distributed in the skin behind the buttocks and sacrum. The hypoluteal cutaneous nerve is a branch of the posterior femoral cutaneous nerve, which goes up around the lower edge of gluteus maximus, passes through the deep fascia and is distributed in the skin below the buttocks. In addition, there are lateral cutaneous branches of iliohypogastric nerve in the lateral skin of buttocks.