The inner thigh is the route of kidney meridian of foot shaoyin, liver meridian of foot jueyin and spleen meridian of foot taiyin. There are six meridians on the leg, namely the kidney meridian of foot shaoyin, the liver meridian of foot jueyin, the spleen meridian of foot taiyin, the bladder meridian of foot taiyang, the gallbladder meridian of foot shaoyang and the stomach meridian of foot Yangming. Kidney meridian, spleen meridian and liver meridian are on the inside of the leg, stomach meridian and gallbladder meridian are on the outside of the leg, and bladder meridian is on the back. Simply put, Sanyang is on the outside of the leg and Yin San is on the inside of the leg.

The twelve meridians, the classified name of meridians, refers to the twelve meridians and its veins. Ling Shu Ben Bo: "Any needling method must pass through the end of the twelve meridians." The twelve meridians is the main body of the meridian system, which has the main characteristics of exterior-interior combination and corresponding zang-fu organs and meridians.