Why do girls have dimples on both sides of their backs?

The "lumbar fossae" are the two concave pits in the waist behind, on both sides of the connection between the sacral vertebrae of the buttocks and the lumbar vertebrae. It is called "McKaisling" in medicine, commonly known as "waist pit", and is also called "holy vortex" in the art world. It is one of the symbols of an ideal human model.

There is no word "lumbar fossa" in anatomy textbooks and academic materials. It can be seen that "lumbar fossa" is not a scientific name and does not have much medical significance. Even "waist nest" is not a common name with a history in the Chinese world. This pair of round dimples has several common names in English: Back Dimple, Butt Dimple, or Dimples of Venus.

Extended information:

The cause of lumbar fossa is currently inconclusive. One theory is that the appearance of lumbar pits may be caused by genetics. There is another possible explanation: there are ligaments pulling each other between the posterior superior iliac spine (qià) and the subcutaneous tissue, plus the muscle and other soft tissue coverage in the area is relatively thin, forming a visible depression that is the lumbar fossa. Relatively speaking, the lumbar pits of people with less subcutaneous fat may be easier to see.

Stretching the back, such as when the body leans forward, stretches upward or kneels, the muscles and other soft tissues are stretched, and the Michaelis diamond fossa on the back of women is more easily exposed.

Baidu Encyclopedia-Waist Nest