二十三难曰∶手足三阴三阳脉之度数，可晓以不？
然∶手三阳之脉，从手走头，长五尺，五六
合三丈。手三阴之脉，从手至胸中，长三尺五寸，三六一丈八尺，五六三尺，合二丈一尺。足三阳之
脉，从足走头，长八尺，六八四丈八尺。足三阴之脉，从足至胸，长六尺五寸，六六三丈六尺，五六
三尺，合三丈九尺。人两足跷脉，从足至目，长七尺五寸，二七一丈四尺，二五一尺，合一丈五尺
督脉任脉，各长四尺五寸，二四八尺，二五一尺，合九尺。凡脉长一十六丈二尺，此所谓十二经脉
长短之数也。
此言十二经脉及两跷督任之脉，析之合之，皆有度数可纪也。手有三阴，太阴肺、少阴心、
厥阴心包络；足有三阴，太阴脾、少阴肾、厥阴肝；手有三阳,太阳小肠、阳明大肠、少阳三焦;足有三阳，太阳
膀胱、阳明胃、少阳胆，为十二经也。经之流注，手三阳皆从手指末起而终于头，手三阴亦从手指末起而终至
胸中，足三阳从足指起而至头，足三阴从足趾足心起而至胸，此举经脉之度数，故皆以手足言也。跷脉属奇经，
有阴阳之分，左右足各有阳跷,即从足太阳申脉穴，由外上行至风池者是也。左右足各有阴跷，即从足少阴照海
穴，由内踝上行至咽喉者是也。但《灵枢·脉度篇》论跷脉起止。专指阴跷言，而不及阳跷，则其长短之数，
乃阴跷之数也。故帝问跷脉有阴阳，何脉当其数，岐伯答以男子数其阳，女子数其阴。盖阳跷与阴跷，虽有内
外表里之殊，其长短则大约相等也。督脉任脉，亦属奇经。督脉起于肾中。由尻贯脊，入脑交巅，终于人中，统一
身之阳。任脉起于少腹之内，出会阴，循脐腹，上喉咙，终于唇下之承浆，统一身之阴。此节引《灵枢·脉度篇》
原文，以明脉即营气也。
经脉十二，络脉十五，何始何穷也？
然∶经脉者，行血气，通阴阳。以荣于身者也。其始从中焦注手太阴阳
明，阳明注足阳明太阴，太阴注手少阴太阳，太阳注足太阳少阴，少阴注手心主少阳，少阳注足少阳厥阴。厥阴
复还注手太阴。别络十五，皆因其原，如环无端，转相灌溉，朝于寸口人迎，以处百病，而决死生也。
上言经脉尺度，此又言经脉行度，而推论络脉随经脉以营运也。经有十二，始从中焦者，盖谓饮食入胃，其
精微之化，注于手太阴阳明，以次相传，至足厥阴，厥阴复还注手太阴也。络
脉十五，皆随十二经脉之所始，转相灌溉，如环之无端，朝会于寸口人迎，以处分百病，而决死生也。
古法以结喉两旁动脉为人迎，越人独取寸口，直以左手关前一分为人迎，右手关前一分为气口，后世宗
之。盖胃受谷气而养五脏，肺朝百脉而平权衡，胃为脉之根，肺为脉之干，胃脉大小强弱，未有不变见
于寸口。寸口者，脉之大会，为肺之动脉，以根干相通故也。
经曰∶明知终始，阴阳定矣，何谓也？
然∶终始者，脉之纪也。寸口、人迎，阴阳之气，通于朝使，
如环无端，故曰始也。终者，三阴三阳之脉绝，绝则死，死各有形，故曰终也。
经，《灵枢·终始篇》也。此节承上文决死生之义，而问脉之终始，以起下节脉绝之形也。终
始篇曰∶凡刺之道，毕于终始，明知终始，五脏为纪，阴阳定矣。是谓欲知终始，于阴阳为能定之，盖
以阳经取决于人迎，阴经取决于寸口也。朝，朝宗也。使，使道也。道即经隧之谓。
始如生物之始，终如生病之穷，欲明生死，脉以候之。阴阳之气，循环不已，人之生机，皆始
于此，故曰始也。三阴三阳之脉绝，人之生机，皆终于此，故曰终也。其三阴三阳脉绝之形状，具如下章。
第二十三难问道：手足三阴经和三阳经的长度，可以讲清楚吗？
回答说：手三阳经的脉气，从手部走向头部，每条长五尺，三条合计为三丈（五尺×6=三丈）。手三阴经的脉气，从手部走向胸中，每条长三尺五寸，三条合计为一丈八尺，再加上六条经脉各余下的半尺共三尺，总计二丈一尺。足三阳经的脉气，从足部走向头部，每条长八尺，六条合计为四丈八尺。足三阴经的脉气，从足部走向胸部，每条长六尺五寸，六条合计为三丈六尺，再加上六条经脉各余下的半尺共三尺，总计三丈九尺。人体左右两条跷脉（奇经八脉之一，主下肢运动及眼睑开合），从足部走向眼部，每条长七尺五寸，两条合计为一丈四尺，再加上两条经脉各余下的半尺共一尺，总计一丈五尺。督脉（奇经八脉之一，总督一身之阳经）和任脉（奇经八脉之一，总任一身之阴经），每条长四尺五寸，两条合计为八尺，再加上两条经脉各余下的半尺共一尺，总计九尺。所有经脉长度加起来一共是一十六丈二尺，这就是所谓的十二经脉长短的数值。
这里讲的是十二经脉以及两跷、督、任四条奇经，分别计算或合并计算，都有固定的长度数据可记录。手有三阴经，分别是太阴肺经、少阴心经、厥阴心包络经；足有三阴经，分别是太阴脾经、少阴肾经、厥阴肝经；手有三阳经，分别是太阳小肠经、阳明大肠经、少阳三焦经；足有三阳经，分别是太阳膀胱经、阳明胃经、少阳胆经，这就构成了十二经脉。经气的流注运行，手三阳经都从手指末端起始而终止于头部，手三阴经也从手指末端起始而终止于胸中，足三阳经从足趾起始而到达头部，足三阴经从足趾和足心起始而到达胸部，这里列举的是经脉的长度度数，所以都用“手”和“足”来指代。跷脉属于奇经，有阴跷和阳跷之分，左右足各有阳跷脉，即从足太阳膀胱经的申脉穴开始，由外踝向上行至风池穴的就是阳跷脉。左右足各有阴跷脉，即从足少阴肾经的照海穴开始，由内踝向上行至咽喉的就是阴跷脉。但是《灵枢·脉度篇》论述跷脉的起止时，专门只指阴跷脉而言，而没有提及阳跷脉，那么其中提到的长短数值，就是阴跷脉的数值。所以黄帝问跷脉有阴阳之分，哪条脉符合这个数值，岐伯回答说是男子计算阳跷，女子计算阴跷。大概因为阳跷与阴跷，虽然在内外表里上有区别，但它们的长度大致是相等的。督脉和任脉，也属于奇经。督脉起于肾中，经过尾闾贯穿脊柱，进入脑部交会于头顶，终止于人中穴，统摄全身所有的阳经。任脉起于小腹之内，出会阴穴，沿着脐腹部上行至喉咙，终止于唇下的承浆穴，统摄全身所有的阴经。这一节引用了《灵枢·脉度篇》的原文，用来说明经脉也就是营气运行的通道。
十二经脉和十五别络，是从哪里开始，又到哪里终结呢？
回答说：经脉，是运行血气，沟通阴阳，以此来濡养身体的。它的起始是从中焦注入手太阴肺经和手阳明大肠经，手阳明大肠经注入足阳明胃经和足太阴脾经，足太阴脾经注入手少阴心经和手太阳小肠经，手太阳小肠经注入足太阳膀胱经和足少阴肾经，足少阴肾经注入手厥阴心包经和手少阳三焦经，手少阳三焦经注入足少阳胆经和足厥阴肝经。足厥阴肝经又回流注入手太阴肺经。十五别络，都是顺着经脉的原穴分出，像圆环一样没有端点，相互转输灌溉，气血朝会于寸口和人迎两处，以此诊治各种疾病，并判断生死预后。
上文说的是经脉的长度尺度，这里又说经脉的气血流注运行规律，进而推论络脉随着经脉来营运气血。经脉有十二条，起始于中焦，是说饮食进入胃中，其精微物质的化生，注入到手太阴肺经和手阳明大肠经，依次相传，直到足厥阴肝经，足厥阴肝经又回流注入手太阴肺经。十五别络，都随着十二经脉的起始之处，相互转输灌溉，像圆环一样没有端点，朝会于寸口和人迎，以此处分治百病，并决断生死。
古法以喉结两旁跳动的动脉为人迎穴，扁鹊（越人）唯独取寸口脉，直接将左手关前一分称为人迎，右手关前一分称为气口，后世医家都遵循这种方法。大概因为胃受纳谷气来滋养五脏，肺朝会百脉来平衡权衡气血，胃是脉的根本，肺是脉的主干，胃脉的大小强弱，没有不在寸口脉上显现出来的。寸口脉，是脉气大会聚的地方，也是肺经的动脉，因为根本与主干相通的原因。
经文说：如果明确知道了终始的道理，阴阳就能确定了，这是什么意思呢？
回答说：终始，是脉气的纲纪。寸口和人迎，阴阳之气，通过朝使之道（经络通道），像圆环一样没有端点，所以称为“始”。所谓“终”，是指三阴三阳的经脉之气断绝，断绝就会死亡，死亡各有其形态表现，所以称为“终”。
这里的“经”，指的是《灵枢·终始篇》。这一节承接上文决断生死的意义，询问脉气的终始，以引出下章关于脉绝形态的内容。《终始篇》说：凡是针刺的道理，都包含在终始之中，明确了终始，就以五脏为纲纪，阴阳就能确定了。这叫做想要了解终始，必须通过阴阳来确定，大概是因为阳经的脉象取决于人迎穴，阴经的脉象取决于寸口穴。“朝”，意思是朝宗、汇聚。“使”，意思是使道，即经隧（经络通道）。
起始就像生命生成的开始，终结就像疾病发展的穷尽，想要明白生死，可以通过脉象来观察。阴阳之气，循环往复不停止，人的生机，都从这里开始，所以称为“始”。三阴三阳的经脉之气断绝，人的生机，都在这里终结，所以称为“终”。至于那三阴三阳经脉断绝的具体形状，详细见如下章节。
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.