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Chapter 23 asks: Can the lengths of the three Yin and three Yang meridians of the hands and feet be explained?

It is answered: The meridians of the three Yang of the hands, flowing from the hands to the head, are five chi long each; six times five chi equals three zhang. The meridians of the three Yin of the hands, flowing from the hands to the chest center, are three chi and five cun long each; three times six (referring to the calculation method in the text) yields one zhang and eight chi, plus five times six (half chi remainder) yields three chi, totaling two zhang and one chi. The meridians of the three Yang of the feet, flowing from the feet to the head, are eight chi long each; six times eight chi equals four zhang and eight chi. The meridians of the three Yin of the feet, flowing from the feet to the chest, are six chi and five cun long each; six times six chi yields three zhang and six chi, plus five times six (half chi remainder) yields three chi, totaling three zhang and nine chi. The two Qiao meridians (Extraordinary Vessels governing lower limb movement and eyelid opening/closing) of the human body, flowing from the feet to the eyes, are seven chi and five cun long each; two times seven chi yields one zhang and four chi, plus two times five (half chi remainder) yields one chi, totaling one zhang and five chi. The Du Mai (Conception Vessel of the Extraordinary Vessels, commanding all Yang meridians of the body) and Ren Mai (Governing Vessel of the Extraordinary Vessels, commanding all Yin meridians of the body) are each four chi and five cun long; two times four chi yields eight chi, plus two times five (half chi remainder) yields one chi, totaling nine chi. The total length of all meridians is sixteen zhang and two chi. This is the numerical value of the lengths of the twelve regular meridians.

This passage discusses the twelve regular meridians as well as the two Qiao, Du, and Ren meridians. Whether analyzed separately or combined, they all have fixed length measurements that can be recorded. There are three Yin meridians of the hand: Taiyin Lung Meridian, Shaoyin Heart Meridian, and Jueyin Pericardium Meridian; there are three Yin meridians of the foot: Taiyin Spleen Meridian, Shaoyin Kidney Meridian, and Jueyin Liver Meridian; there are three Yang meridians of the hand: Taiyang Small Intestine Meridian, Yangming Large Intestine Meridian, and Shaoyang Sanjiao Meridian; there are three Yang meridians of the foot: Taiyang Bladder Meridian, Yangming Stomach Meridian, and Shaoyang Gallbladder Meridian. These constitute the twelve regular meridians. Regarding the flow and transmission of Jing-Qi (Meridian Qi), the three Yang meridians of the hand all originate from the tips of the fingers and terminate at the head; the three Yin meridians of the hand also originate from the tips of the fingers and terminate in the chest center; the three Yang meridians of the foot originate from the toes and reach the head; the three Yin meridians of the foot originate from the toes and sole of the foot and reach the chest. Here, the lengths of the meridians are listed, hence "hand" and "foot" are used to refer to them. The Qiao meridians belong to the Extraordinary Vessels and are divided into Yin and Yang. Each foot has a Yang Qiao meridian, which starts from Shenmai (BL62) of the Taiyang Bladder Meridian and ascends externally to Fengchi (GB20); this is the Yang Qiao. Each foot has a Yin Qiao meridian, which starts from Zhaohai (KI6) of the Shaoyin Kidney Meridian and ascends internally from the medial malleolus to the throat; this is the Yin Qiao. However, in the *Mai Du* chapter of the *Ling Shu*, when discussing the origin and termination of the Qiao meridians, it specifically refers only to the Yin Qiao and does not mention the Yang Qiao. Therefore, the length values mentioned therein are those of the Yin Qiao. Thus, when the Yellow Emperor asked about the Yin and Yang of the Qiao meridians and which one corresponded to these numbers, Qibo answered that for men, the Yang Qiao is measured, and for women, the Yin Qiao is measured. Generally speaking, although the Yang Qiao and Yin Qiao differ in their internal/external and superficial/deep locations, their lengths are approximately equal. The Du Mai and Ren Mai also belong to the Extraordinary Vessels. The Du Mai originates in the Kidneys, passes through the sacrum and spine, enters the brain, meets at the vertex, and terminates at the Renzhong point (GV26), commanding all Yang meridians of the body. The Ren Mai originates within the lower abdomen, emerges at Huiyin (CV1), follows the umbilicus and abdomen, ascends to the throat, and terminates at Chengjiang (CV24) below the lip, commanding all Yin meridians of the body. This section quotes the original text from the *Mai Du* chapter of the *Ling Shu* to clarify that the meridians are the pathways of Ying-Qi (Nutritive Qi).

What are the origins and terminations of the twelve regular meridians and the fifteen collaterals?

It is answered: The regular meridians transport Blood and Qi, connect Yin and Yang, and thereby nourish the body. Their flow begins at the Middle Jiao, entering the Hand-Taiyin Lung Meridian and Hand-Yangming Large Intestine Meridian; the Hand-Yangming Large Intestine Meridian flows into the Foot-Yangming Stomach Meridian and Foot-Taiyin Spleen Meridian; the Foot-Taiyin Spleen Meridian flows into the Hand-Shaoyin Heart Meridian and Hand-Taiyang Small Intestine Meridian; the Hand-Taiyang Small Intestine Meridian flows into the Foot-Taiyang Bladder Meridian and Foot-Shaoyin Kidney Meridian; the Foot-Shaoyin Kidney Meridian flows into the Hand-Jueyin Pericardium Meridian and Hand-Shaoyang Sanjiao Meridian; the Hand-Shaoyang Sanjiao Meridian flows into the Foot-Shaoyang Gallbladder Meridian and Foot-Jueyin Liver Meridian. The Foot-Jueyin Liver Meridian then returns to flow into the Hand-Taiyin Lung Meridian. The fifteen distinct collaterals branch off from the Yuan-Source points of the meridians, forming a cycle without beginning or end, irrigating each other in turn. Their Qi converges at the Cun Kou (Radial Artery) and Ren Ying (Carotid Artery) sites to diagnose various diseases and determine life and death.

The previous section discussed the physical lengths of the meridians; this section discusses the functional flow of Qi within the meridians and deduces how the collaterals operate along with the meridians. The twelve regular meridians begin at the Middle Jiao, meaning that after food enters the Stomach, its refined essence is transformed and injected into the Hand-Taiyin Lung Meridian and Hand-Yangming Large Intestine Meridian, passing sequentially until it reaches the Foot-Jueyin Liver Meridian, which then returns to flow into the Hand-Taiyin Lung Meridian. The fifteen collaterals follow the origins of the twelve regular meridians, irrigating each other in turn like a circle without end, converging at the Cun Kou and Ren Ying sites to differentiate and treat hundred diseases, and to decide upon life and death.

Ancient methods identified the pulsating artery on both sides of the laryngeal prominence as the Ren Ying point. Bian Que (Yue Ren) exclusively took the Cun Kou pulse, directly designating the one-fen anterior to the Guan position on the left hand as Ren Ying, and the one-fen anterior to the Guan position on the right hand as Qi Kou. Later generations followed this practice. This is because the Stomach receives grain Qi to nourish the Five Zang Organs, and the Lung gathers the Hundred Meridians to balance and weigh the Qi. The Stomach is the root of the pulses, and the Lung is the trunk of the pulses. The size and strength of the Stomach's pulse invariably manifest at the Cun Kou. The Cun Kou is the great gathering of pulses and the arterial site of the Lung; thus, they communicate via root and trunk.

The Classic states: "If one clearly understands the Beginning and End, Yin and Yang are determined." What does this mean?

It is answered: The Beginning and End are the principles of the pulses. At the Cun Kou and Ren Ying, the Qi of Yin and Yang communicates through the channels of assembly and dispatch, forming a cycle without beginning or end; therefore, it is called the "Beginning." The "End" refers to the cessation of the Qi of the Three Yin and Three Yang meridians. When they cease, death occurs. Death presents with specific forms; therefore, it is called the "End."

The "Classic" here refers to the *Zhong Shi* (Beginning and End) chapter of the *Ling Shu*. This section continues the meaning of determining life and death from the previous text by asking about the beginning and end of the pulses, leading into the description of the forms of pulse cessation in the following chapter. The *Zhong Shi* chapter states: "All methods of acupuncture are completed in the Beginning and End. If one clearly understands the Beginning and End, the Five Zang become the principle, and Yin and Yang are determined." To know the Beginning and End, one must determine them through Yin and Yang, generally meaning that the pulses of Yang meridians are judged by the Ren Ying point, and the pulses of Yin meridians are judged by the Cun Kou point. "Chao" means to gather or pay homage. "Shi" means the channel of dispatch, i.e., the meridians.

The Beginning is like the start of biological generation; the End is like the exhaustion of disease pathology. To understand life and death, one observes the pulses. The Qi of Yin and Yang circulates endlessly; human vitality begins here, hence it is called the "Beginning." The cessation of the Qi of the Three Yin and Three Yang meridians marks where human vitality ends, hence it is called the "End." The specific manifestations of the cessation of the Three Yin and Three Yang meridians are detailed in the following chapters.