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In the human body, there are Jing (Primary Meridians) and Luo (Collaterals). Those that run straight are called Jing, while those that branch off are called Luo. There are twelve primary meridians, namely the Three Yin and Three Yang meridians of the hand and foot.

The fifteen collaterals consist of one collateral from each of the twelve primary meridians, plus one major collateral from the Spleen, along with the Ren (Conception Vessel) and Du (Governing Vessel) collaterals, totaling fifteen collaterals. Together with the twenty-four qi flows of the twelve meridians, these constitute twenty-seven qi streams. They circulate up and down continuously, like flowing spring water or the movement of the sun and moon, never resting. Thus, Yin meridians nourish the Zang organs, and Yang meridians nourish the Fu organs. The Yin and Yang meridians interconnect in a continuous cycle without beginning or end. Without understanding this principle, one cannot grasp how it repeats endlessly. The overflowing qi enters the Eight Extraordinary Vessels, irrigating each other, moving internally to the Zang-Fu organs, and moistening externally the Couli (skin texture and pores).

There are eight extraordinary vessels, which are not constrained by the twelve primary meridians and lack exterior-interior pairing; hence they are termed "Extraordinary." These vessels are likened to lakes and marshes: when the qi of the primary meridians becomes abundant, it overflows into the extraordinary vessels. Qin Yue-ren (Bian Que) compared this to rain falling from heaven, causing ditches and channels to overflow, with surging waters spreading sideways into lakes and marshes. This elucidates the secrets of the *Ling Shu* and *Su Wen*. The eight vessels are scattered across various texts. Although I am not talented, I will attempt to outline their main principles. The eight vessels are: Yin Wei Mai, Yang Wei Mai, Yin Qiao Mai, Yang Qiao Mai, Chong Mai, Ren Mai, Du Mai, and Dai Mai.

Yang Wei Mai originates at the convergence of all Yang meridians and ascends from the lateral malleolus into the Wei (Defensive) level, serving as the framework for the exterior of the body. Yin Wei Mai originates at the convergence of all Yin meridians and ascends from the medial malleolus into the Ying (Nutritive) level, serving as the framework for the interior of the body.

Yang Qiao Mai originates in the heel, follows the lateral malleolus, and ascends along both sides of the body, enabling agility of the joints. Yin Qiao Mai also originates in the heel, follows the medial malleolus, and ascends along both sides of the body.

Du Mai (Governing Vessel) originates at Huiyin (CV1), runs along the back, and governs all Yang meridians, thus being called the "Sea of Yang Meridians." Ren Mai (Conception Vessel) also originates at Huiyin (CV1), runs along the abdomen, and governs all Yin meridians, thus being called the "Sea of Yin Meridians." Chong Mai (Penetrating Vessel) originates at Huiyin (CV1), runs alongside the umbilicus, and ascends directly upward, acting as the crucial passage for all meridians, thus being called the "Sea of the Twelve Primary Meridians." Dai Mai (Girdle Vessel) encircles the waist horizontally, resembling a belt, thereby binding and regulating all meridians.

Therefore, Yang Wei Mai governs the exterior of the body, and Yin Wei Mai governs the interior, corresponding to Qian (Heaven) and Kun (Earth). Yang Qiao Mai governs the Yang on both left and right sides, and Yin Qiao Mai governs the Yin on both left and right sides, corresponding to East and West. Du Mai governs the Yang at the posterior, and Ren Mai governs the Yin at the anterior, corresponding to North and South. Dai Mai binds the meridians horizontally, corresponding to the Six Directions (Liu He). Among the eight vessels, only Ren Mai and Du Mai correspond to the Zi-Wu (North-South axis) of the body, serving as the pathways for the ascent and descent of Qi and the site of Yin-Yang interaction. Just as deer move their tails to stimulate the Du Mai and replenish essence, and turtles breathe through their noses to stimulate the Ren Mai and replenish Qi, these animals achieve longevity. This is the gist of the Eight Extraordinary Vessels. For specific acupoints and symptoms, please refer to *Binhu Maixue* (Pulse Studies by Binhu).