The twelve meridians are the main part of the meridian system and are divided into three yang and three yin meridians, totaling twelve. The division of yin and yang is mainly based on the circulation of the meridians, as well as the yin and yang properties of the internal organs to which the meridians belong. 1. The circulating parts of meridians: the inner limbs and the chest and abdomen are yin, the outer limbs and the back of the shoulders, head and face are yang. In the limbs, head and face, in front of the Taiyin, Yangming, in the middle (side) for the syncopated yin, Shaoyang, in the back of the Shaoyin, the sun (8 inches above the ankle, syncopated yin is located in the Taiyin after). 2. Meridians belonging to the internal organs: on the basis of the circulation of the hands and feet, according to the meridians corresponding to the yin and yang properties of the internal organs and then divided into yin and yang, dirty for the yin, internal organs for the yang. Such as lung for the yin in the yang, it should be in the hand Taiyin, heart for the yang in the yang (yin less), it should be in the hand Shaoyin, liver for the yin in the yang (yin least), it should be in the foot of the syncopated yin, the spleen for the yin in the yin (yin the most), it should be in the foot of the Taiyin, according to which the meridians of the yin and yang divisions.