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Wang Ang's Commentary: The Eight Extraordinary Vessels have been discussed in detail by predecessors. According to Li Shizhen, the Yang Linking Vessel (Yangwei Mai) originates at the intersection of all Yang vessels, ascends from the lateral malleolus into the Wei (Defensive) level; the Yin Linking Vessel (Yinwei Mai) originates at the intersection of all Yin vessels, ascends from the medial malleolus into the Ying (Nutritive) level; thus serving as the framework for the body's vessels. The Yang Heel Vessel (Yangqiao Mai) originates in the middle of the heel, ascending along the lateral malleolus on both sides of the body; the Yin Heel Vessel (Yinqiao Mai) originates in the middle of the heel, ascending along the medial malleolus on both sides of the body; thus enabling agility of the joints. The Du Meridian (Du Mai) originates at Huiyin (CV1), runs along the back posteriorly, acting as the chief director of all Yang vessels, hence called the "Sea of Yang Vessels"; the Ren Meridian (Ren Mai) originates at Huiyin (CV1), runs along the abdomen anteriorly, acting as the supporter of all Yin vessels, hence called the "Sea of Yin Vessels". The Chong Meridian (Chong Mai) originates at Huiyin (CV1), flanking the umbilicus and rushing upward, serving as the crucial passage for all vessels, hence called the "Sea of the Twelve Regular Vessels". The Dai Meridian (Dai Mai) encircles the waist horizontally, resembling a belt, thereby binding and regulating all other vessels. Therefore, the Yang Linking Vessel governs the exterior of the body, and the Yin Linking Vessel governs the interior, speaking in terms of Qian and Kun; the Yang Heel Vessel governs the left and right Yang aspects of the body, and the Yin Heel Vessel governs the left and right Yin aspects, speaking in terms of East and West; the Du Meridian governs the posterior Yang, while the Ren and Chong meridians govern the anterior Yin, speaking in terms of North and South; the Dai Meridian binds the vessels horizontally, speaking in terms of the Six Directions. Furthermore, Zhang Jiegou stated that "Qiao" means agility. These two vessels originate from the feet, granting agility to movement. The Yang Heel Vessel lies above the muscles, following the path of Yang vessels, penetrating the Six Fu Organs, and governing the exterior, hence named the collateral of the Yang Heel. The Yin Heel Vessel lies below the muscles, following the path of Yin vessels, penetrating the Five Zang Organs, and governing the interior, hence named the collateral of the Yin Heel. Observing these discussions on the Eight Extraordinary Vessels, although they exist outside the Twelve Regular Vessels and are named "Extraordinary," they also serve as assistants to the regular vessels and collaterals. Generally, the regular vessels are like ditches on the earth, while the extraordinary vessels are like lakes and marshes outside these ditches. If the ditches of the regular vessels do not dry up, the lakes of the extraordinary vessels will not become extremely depleted; if the water in the ditches of the regular vessels overflows, the lakes of the extraordinary vessels will inevitably be irrigated. Thus, the ancients said: When the Qi of the Zang organs is harmonious and the vessels are smooth, no abnormal manifestations of the Eight Extraordinary Vessels can appear; even if pathogens invade the vessels, they will not overflow, having no relation to the extraordinary vessels. However, if the pathogenic heat in the vessels becomes excessive, it will inevitably overflow into the extraordinary vessels. This is akin to rain falling, causing ditches to overflow, with heavy rains flowing wildly into the lakes, which is consistent with this meaning. Moreover, each regular vessel is paired with a Zang or Fu organ, whereas the extraordinary vessels have their own origins and endings, differing from the regular vessels' pattern; thus, the extraordinary vessels act as constraints for the Twelve Regular Vessels. Therefore, in Shanghan (Cold Damage) diseases, pathogens may start from the Yang Linking Vessel and sequentially transmit to the Three Yang vessels, or start from the Yin Linking Vessel and sequentially transmit to the Three Yin vessels. Additionally, when internal Zang Qi stagnates and external pathogens overflow, they may directly affect the extraordinary vessels first. However, this occurs because pathogens enter internally and do not remain in the extraordinary vessels, unlike the situation where heat in the Twelve Regular Vessels necessarily overflows into the extraordinary vessels. Li Shizhen said: If a physician understands the Eight Extraordinary Vessels, they grasp the main principles of the Twelve Regular Vessels and Fifteen Collaterals; if an immortal understands them, they comprehend the mysteries of the rising and lowering of Dragon and Tiger, and the subtle apertures of Xuanpin. He also said: A physician who does not know this cannot probe the disease mechanism; an immortal who does not know this cannot stabilize the furnace and tripod. These words are profound. I record this to assist physicians.

The Ren Meridian originates from the bottom of Zhongji (CV3, four cun below the umbilicus, acupoint name Zhongji). The Ren Meridian starts below this point, at the intersection of the two yins, the Huiyin acupoint. The Ren Meridian travels from Huiyin through the abdomen, while the Du Meridian travels from Huiyin through the back. It passes above the pubic hair, running within the abdomen (passing through Zhongji acupoint), ascends to Guanyuan (CV4, three cun below the umbilicus, acupoint name), reaches the throat, ascends to the chin, follows the face, and enters the eyes (connecting with Chengqi ST1).

The Chong Meridian originates at Qichong (ST30) and joins the Shaoyin Kidney Meridian, ascending alongside the umbilicus to the chest (The Ren Meridian ascends through the umbilicus, while the Chong Meridian ascends beside it. All above content is from Suwen, Chapter 68: Bone Empty Discourse). The Chong Meridian is the Sea of the Five Zang and Six Fu Organs (Chong is the Sea of Blood), receiving Qi from the Five Zang and Six Fu Organs. It渗irrigates the Yang vessels upwards (emerging at Hangsang), taking its name "Chong" (Rushing) from the upward rush from below. There are also branches descending with the Kidney, injecting into the Shaoyin collateral, emerging at Qichong, entering the medial aspect of the thigh, and entering the popliteal fossa (the bend behind the knee), running deep within the tibia near the medial malleolus. It downwardly irrigates the Three Yin vessels (Liver, Spleen, Kidney) and the various collaterals, warming the muscles down to the dorsum of the foot and toes (following the sole of the foot down to Yongquan KI1, entering the big toe. This section is from Lingshu, Chapter 52: Reverse and Smooth, Fat and Thin).

The Du Meridian originates from the center of the lower abdominal bone, entering and connecting to Tingkong (the end of the female clitoris and urethral opening, i.e., Yaolou acupoint), connecting to the genitalia. It meets at Cu Jian (the junction of the two yins, named Cu), then diverges posteriorly around the buttocks, joining the Chenyang collateral (Taiyang mid-collateral) and comparing with the Shaoyin (combining with the Bladder and Kidney meridians). It ascends along the posterior-medial aspect of the thigh, penetrates the spine, attaches to the Kidney, ascends together with the Taiyang Meridian starting from the inner canthus of the eye. It ascends to the forehead, crosses the vertex, connects to the brain, descends to the nape, follows the shoulder (inner arm), and still runs alongside the spine. It reaches the waist, connects to the Kidney (this part of the Du Meridian runs parallel with the Taiyang), follows the male penis, descends to Cu Jian, similar to females. It again penetrates from the lower abdomen through the umbilicus, penetrates the Heart, enters the throat, reaches the chin and lips (encircling the lips). It ascends to connect to the center below the eyes, running parallel with the Ren Meridian (this part of the Du Meridian runs parallel with the Ren Meridian), and also parallels the Chong Meridian. Generally, these three meridians share the same root (Chong, Ren, and Du all originate below Huiyin, one source branching into three, different names but same substance). Ling Shu and Su Wen mention them with some complexity (Ling Shu, Chapter 49: Five Tones and Five Flavors states: Chong and Ren meridians both originate in the chest, ascending along the back interior. This again states Chong and Ren run on the back. Hence, some scriptures refer to the Chong Meridian as the Du Meridian. Ancient atlases call the Ren Meridian running on the back "Du", and the one rising straight from the lower abdomen "Ren", also calling it "Du". Modern people generally consider the one running on the back as Du, the one on the front as Ren, and the one rising from the center as Chong. However, examining the acupoints of the Ren and Du meridians, one is on the front of the body, one on the back; while the Chong Meridian is central, it has no acupoints. It seems appropriate to regard this explanation as correct). Du Meridian pathology manifests as pain rushing from the lower abdomen to the heart, inability to pass stool and urine (obstruction of both bowels and urination), and Chong Hernia attacks (this Du pathology is similar to Chong pathology). In women, it manifests as infertility (Chong is the Sea of Blood, Ren governs the uterine collaterals), dry throat (meridian follows the throat), enuresis, and hemorrhoids/strangury (connects to genitalia, meets at Cu Jian. This Du pathology is similar to Ren and Chong pathology). Ren Meridian pathology: in men, hernia (internal knotting of seven types of hernia); in women, leukorrhea and masses (leukorrhea and masses are women's hernias). Chong Meridian pathology: internal urgency and Qi counterflow (blood deficiency causes urgency, Qi excess causes counterflow. This section is from Suwen, Chapter 68: Bone Empty Discourse. Du leads the vessels of all meridians. Chong means Qi rushes upward. Ren means women receive nourishment through it).

The Yin Heel Vessel is a branch of the Shaoyin (Kidney) Meridian, originating behind Ran Gu (below the large bone of the medial malleolus, Zhaohai KI6) to the medial malleolus. It goes straight up the medial thigh into the genital region, ascends along the chest into the Supraclavicular Fossa, passes anterior to Renying (ST9, Stomach Meridian, carotid artery in the neck), enters the cheekbone, reaches the inner canthus of the eye (Jingming BL1), and merges with the Taiyang Meridian and the Yang Heel Vessel (Yang Heel Vessel starts at Shenmai BL62, in the depression below the lateral malleolus. This section is from Ling Shu, Chapter 27: Pulse Degrees). These are all explanations of the extraordinary vessels in Ling Shu and Su Wen; the Dai Meridian and the Two Linking Vessels are not detailed here.