The concept of yin and yang representing the two archetypical or universal polarities [1] is a fundamental principle of Chinese medicine [2]. It is particularly relevant to the practice of acupuncture.SummaryWhen this information is presented graphically, it is clear that what we normally refer to as the back of the body is essentially part of the yang surface. The soles of the feet, the inner thigh, and the skin over the flexor carpi ulnaris muscle are all that can be seen from the rear and can be considered as part of the yin surface.