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Twelve Regular Meridians, Fifteen Collaterals, Regular Meridians, Six Pairs of Interior-Exterior Connections, Five Shu Points, Six Yuan Source Points, Four Passes, Twelve Muscle Regions (Jin).

The so-called meridians and collaterals: those that run straight are the **Regular Meridians** (Jing, 经), and those that branch off are the **Collaterals** (Luo, 络). The straight-running ones are unobstructed, connecting the interior and exterior, left and right, upper and lower, circulating without stagnation, like the flow of rivers. They serve as the pathways for the fifty circuits completed in a day and night. This is what is called the "Meridian" (Jing). Those that loop back, intersect, and belong to the Zang organs, which do not travel along the main thoroughfares, are called "Collaterals" (Luo). The *Ling Shu* states: The three Yin meridians of the hand travel from the abdomen to the hand; the three Yang meridians of the hand travel from the hand to the head; the three Yang meridians of the foot travel from the head to the foot; the three Yin meridians of the foot travel from the foot to the abdomen. The abdomen is the convergence of Yin, and the head is the gathering place of Yang. Yin connects with Yin at the abdomen, and Yang connects with Yang at the head. The three Yin meridians turn to enter the Yang meridians at the fingertips of the hands, and the three Yang meridians turn to enter the Yin meridians at the fingertips of the feet. This is entering Yang through Yin and entering Yin through Yang, reaching everywhere. What circulates and runs straight is the "Meridian" (Jing).

However, among them, there are intersecting and linking branches. The six Yang meridians originate from the head and each descend into the **Quepen** (ST12, Clavicular Fossa), internally connecting and networking with the five Zang organs. The meridians of the five Zang organs also ascend to the throat, the eye system, the root of the tongue, and the vertex. These are the side-branching parts of the regular meridians, not traveling through the main tunnels, thus constituting the "Collaterals" (Luo). Yet, these side-branching collaterals actually intersect with the body. The five Zang and six Fu organs have specific locations where their refined Qi gathers. These gatherings reach specific points, such as **Gongsun** (SP4), **Dabao** (SP21), **Xuli** (RN15), and **Qimen** (LR14), forming the fifty **Extraordinary Collaterals** (Jingbie, 经别) of the meridians. These collaterals are grand and vigorous, comparable to the meridians themselves, but because they branch off sideways and do not follow the main tunnels, they are called "Extraordinary Collaterals" (Jingbie) and also belong to the category of "Collaterals" (Luo).

The term "Regular Meridians' Six Pairs" (Jingzheng Liuhe, 经正六合) refers to the fact that the regular meridians are rooted in the Zang and Fu organs, each having its own territorial domain. Besides circulating through the main tunnels, the adjacent territories naturally have surplus connections. There are further exchanges and distributions, some belonging to the same meridian, naturally connecting with the interior-exterior and Yin-Yang pairs of that meridian. This forms the interior-exterior connections, totaling six pairs, representing the mutual association of Zang and Fu organs. Since these connections do not lie within the main tunnels but rather associate through the territorial domains of the respective meridians, they are not "Extraordinary Collaterals" (Jingbie) but "Regular Meridian Alignments" (Jingzheng). From the aforementioned twelve regular meridians and fifteen collaterals, combined with the six alignments of each meridian, there are twenty-seven Qi flows that circulate throughout the body. All looping Qi and major gatherings occur here.

Regarding the **Five Shu Points** (Wushu, 五输), **Six Yuan Source Points** (Liuyuan, 六原), and **Four Passes** (Siguan, 四关): these refer to the critical junctures in the main tunnels of the hands and feet. Generally, the Yuan Source points of the twelve meridians all originate at the ten fingers of the hands and feet. These are the sites where the refined Qi of each Zang and Fu organ originates, gathers, and enters. Thus, they are classified into Jing (Well), Ying (Spring), Shu (Stream), Jing (River), Yuan (Source), and He (Sea) points. The five Zang correspond to the five Shu points, and the six Fu correspond to the six Yuan points, recorded accordingly. All fall within the scope of the "Four Passes." To treat diseases of the Zang and Fu organs, these critical junctures are named "Passes" (Guan).

Generally, the concepts of meridians and collaterals encompass two meanings. One relates to the circulation of Qi and Blood: inhaling moves it three cun, exhaling moves it three cun, completing fifty circuits in a day and night. The diagnostic criterion is observing whether the pulse beats fifty times without interruption. This assesses the flowing Qi. The other relates to the origin of points: Jing, Ying, Shu, and Yuan points are assessed based on the territorial distribution of the five Zang and six Fu organs. This is similar to diagnosing via the Cun, Guan, and Chi positions of the radial artery, as hidden pathologies cannot be concealed. This assesses the non-flowing aspects (pathological stagnation). Only the essence of the pulse reveals both flowing and non-flowing states, allowing one to guard the narrow passages of the meridians and diagnose hundreds of diseases. Nothing is more precise than this.

Furthermore, humans have the **Twelve Muscle Regions** (Shier Jingjin, 十二经筋). The Jin (sinews/tendons) are distributed throughout the body, serving as the structural support. They originally belong to the Lung, dividing and maintaining the territories of each meridian, hence the name "Twelve Muscle Regions." The Yang muscle regions are external and firm/hard. When diseased, it is usually due to external Wind, Cold, or Dampness invading, resulting in Bi syndrome (painful obstruction). Thus, the symptoms follow the order of the meridians. The Yin muscle regions are internal and soft/fine. However, they are distributed at pivotal points and often coordinate with the meridians. Therefore, if Phlegm stagnates or Nutritive Qi is obstructed, they can also lead to epilepsy or convulsions, differing from external muscle region diseases. This is the general overview of Jin diseases. Zhang Zihe stated that any physician must understand the roots, endings, beginnings, and ends, the loops, gatherings, intersections, and passages of the meridians. Only then can one comprehend the entry and exit, deficiency and excess of Yin-Yang and Zang-Fu organs. Those who do not know this are like facing a wall (ignorant).