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The yin and yang primordial qi (Yuan Qi, 元气) of the human body all originate from the lower part. Therefore, after discussing "Guangming" (Broad Enlightenment), the *Neijing* (Inner Canon) immediately mentions "Taichong" (Great Surge). The area of Taichong belongs to Shaoyin (Lesser Yin). Anterior to Shaoyin is Jueyin (Terminal Yin), whose region is known as the Sea of Blood (Xue Hai, 血海), which frequently surges essence and qi together with Taichong, irrigating and permeating the yin and yang above. Thus, the primordial qi and essence of humans all originate from below. However, rising from below, they divide into three pathways ascending: the yang pathway travels posterior to Shaoyin, running through the midline between the spine within the Taiyang (Greater Yang) meridian, thereby commanding all yang meridians; this vessel is named the Du Mai (Governor Vessel, 督脉). The yin pathway ascends from the anterior yin earth path, entering the exterior-interior relationship of the Yangming (Yang Brightness) meridian, thereby commanding all yin meridians; this vessel is named the Ren Mai (Conception Vessel, 任脉). The central pathway originates from the Sea of Blood, surging essence and qi upward to accumulate in the chest, forming Zong Qi (Gathering Qi, 宗气) to govern respiration; this vessel is named the Chong Mai (Penetrating Vessel, 冲脉). This qi resides in the Middle Jiao (Central Region, 中州) along with the Stomach Qi of Yangming, and also travels with Ying Qi (Nutritive Qi, 营气) through the twelve meridians.

I have examined that the Du Mai originates in the Bao Zhong (Uterus/Bladder Center, 胞中), ascends to the vertex, passing through Baihui (GV20) and Shenting (GV24); the Ren Mai originates below Zhongji (CV3) in the Bao Zhong, follows Guanyuan (CV4) and passes Chengjiang (CV24), meeting the Du Mai above; the Chong Mai originates in the Bao Zhong, ascends alongside the umbilicus, and meets at the throat. These three vessels originate from the Xia Ji (Lower Extreme/Huiyin, 下极), sharing one source but branching into three. Therefore, the Sages do not speak of Chong, Du, and Ren separately, but collectively name them "Taichong." Taichong refers to the ascent of the essence and qi of the whole body, not merely referring to the Sea of Blood.

Between the interior and exterior lies the Dai Mai (Belt Vessel, 带脉), which runs horizontally. It crosses the hypochondriac region, governed by Zhangmen (LR13) and Wushu (GB25), binding all meridians to maintain regularity above and below, restraining Ying Qi so it does not become lax. Its shape resembles a belt tied around the person hanging down in front, serving as a lock for essence and qi. This area is called "Lv" (Muscles of the Back, 膂), where the body's full strength emerges; the persistence of Lv Li (Back Strength, 膂力) is due to this.

"Wei" (Maintain, 维) implies maintenance and connection. While Yang meridians are commanded by the Du Mai and Yin meridians by the Ren Mai, there are specific vessels that must connect and support the scattered and converging points of these yin and yang meridians. Thus, there is the Yin Wei Mai (Yinkling Vessel, 阴维脉) to connect the yin meridians, and the Yang Wei Mai (Yangkling Vessel, 阳维脉) to connect the yang meridians. However, those capable of connecting must start from the root of yin and yang, possessing the vigorous emission of qi before they can connect. The Yang Wei Mai goes from Shaoyin to Taiyang, originating from Jinmen (BL63) of the Foot-Taiyang meridian, and meets five meridians (Hand-Shaoyang, Foot-Shaoyang, Hand-Yangming, Foot-Yangming) at Yangbai (GB14). The Yin Wei Mai slants from Shaoyin to Jueyin, originating from Zubin (KI9) of the Foot-Shaoyin meridian, ending at the front of the vertex. Shaoyin and Shaoyang are the root qi of yin and yang. Connecting yang must start from Shaoyin, indicating that yin is the root of yang. Connecting yin must start from Shaoyang, indicating that yang guides yin. Therefore, these two vessels are also the guidelines for Ying Qi.

The two Qiao Mai (Yinqiao and Yangqiao, 跷脉) derive their meaning from "Qiao," which signifies lifting or striding. Their qi is swift and fierce, similar to Wei Qi (Defensive Qi, 卫气), and both ascend to the eyes. However, their pathways differ from Wei Qi. The Yin Qiao emerges from yang and intersects with the Foot-Taiyang meridian, while the Yang Qiao enters yin and intersects with the Foot-Shaoyin meridian. Their qi and movement often arise from the harmony of the roots of yin and yang, enabling striding and ascending to nourish the head, converging at the eyes, thus ensuring proper opening and closing of the eyes. The statement "Yin meridians nourish the Zang organs, Yang meridians nourish the Fu organs" means that entering yin nourishes the Zang, and entering yang nourishes the Fu.

Regarding men and women, their pulse characteristics differ based on function: Men utilize yang, so their Qiao Mai focuses on yang; thus, men's pulses are predominantly associated with yang. Women utilize yin, so their Qiao Mai focuses on yin; thus, women's pulses are predominantly associated with yin. In summary, among the Eight Extraordinary Vessels, only the Dai Mai binds horizontally at the waist and back, while the other seven vessels pillar upwards from below. Although they have distinct pathways and numerous convergence points, since they all originate from Taiyang and Shaoyin, they all embody the meaning of "Taichong." Therefore, the Sages only mention Taichong and do not separately discuss Du, Ren, Wei, and Qiao, implying a relationship that is differentiated yet unified.