二十五难曰∶有十二经，五脏六腑十一耳，其一经者，何等经也？
然∶一经者，手少阴与心主别
脉也。心主与三焦为表里，俱有名而无形，故言经有十二也。
此节问答之意，谓五脏六腑配手足之阴阳，但十一经耳，其一经者，乃手少阴心脉，手心主包络脉
也。二脉俱是心脉，而少阴与太阳合脉，心主与三焦合脉，各相表里而合为十二经也。其言包络三焦无
形者，言其气也，然未免语病。《灵枢·本藏篇》曰∶密理浓皮者，三焦膀胱浓，粗理薄皮者，三焦膀胱
薄。果否无形，何以有浓薄之相应乎？邪客篇曰∶心者，五脏六腑之大主，其脏坚固。邪弗能容，容之则
心伤，心伤则神去而死矣。故诸邪之在于心者，皆在于心之包络。包络者，言包裹此心之膜也。若其无
形，所指何物？是包络三焦之有形，不待辨自明矣。
按∶手厥阴心包络，即包心之脂膜，西医谓心外之夹膜者是也。其膜分内外二层，外层浓而坚密，
上裹总回管脉管，下与膈膜之上层相粘，内层外连于外层，内粘于心，其脉与膈之脉管，肺之气食两管，
而通贯于脑筋。心之脉络，亦从包络发出，以达周身。故经言膻中者，臣使之官也。手少阳三焦，为水中
之阳，是为相火。经言少阳属肾者，属于肾中命门也。命门即肾系，
由肾系下生脂膜，为三焦之根。西医所谓腹包膜，腹内腑统膜者是也。其膜之原，肾系之，下裹膀胱，
通两肾，包二肠及女子子宫，经核反折回，由尻骨之后上行腹壁膜，前至肝之上，膈膜之下，转向腹
前，包肝裹胃，上层与膈膜之下层粘续。膈之上层，与心包络之下层相联，气脉通贯于肝之下，胃之
上，又横出薄膜一层，以隔肝胃，即肝胃连膜也。心肺在此膜之上，不能包裹，所包各脏腑，肚腹之
前，成一空囊，由肝胃连膜，后有一孔相通，透入空囊，名曰空窍。凡膈膜以下各脏腑之间，俱有此膜
数层之折叠筋带，为绾其脏腑，以定其部位，并护行各处之血管脑筋，又枝生薄膜，网罗纵横，是由
彼脏行于此脏，以通气血者也。凡诸连网膜油，皆三焦之物也。夫包络之脉，下膈，历络三焦上下，
粘续其气；并出于肾，一游行于上中下三焦，而各有所归之部署；一入于心包络，而为君主之相。三
焦起于七节之间，藏水中真火，为相火之宅，包络乃相火之脏，三焦乃相火之腑，包络三焦气化流行，
皆相火之流行也。以似脏别脏之小囊，配似腑外腑之大囊，亦天造地设之理，不容妄议者也。若泥执
无形，误矣。
第二十五难问道：人体有十二经脉，但五脏六腑加起来只有十一个脏器（五脏加六腑），那么多出来的这一条经脉，究竟是哪一条经脉呢？
回答说：多出的这一条经脉，是手少阴心经与心包络（即心主）各自独立的经脉。心包络与三焦互为表里，它们虽然有名分却看似没有固定形态，所以说经脉共有十二条。
这段问答的意思是，五脏六腑配合手足的阴阳属性，实际上只对应十一条经脉。那多出来的一条，就是手少阴心脉和手厥阴心包络脉。这两条脉都属于心的脉络，其中手少阴经与手太阳小肠经相合为表里，手厥阴心包络经与手少阳三焦经相合为表里，各自构成表里关系，从而合为十二条经脉。文中说心包络和三焦“无形”，是指它们的“气”而言，但这说法难免有语病。《灵枢·本藏篇》说：“皮肤纹理细密、皮厚的人，其三焦和膀胱的膜也厚；皮肤纹理粗糙、皮薄的人，其三焦和膀胱的膜也薄。”如果三焦真的无形，怎么会有厚薄的相应变化呢？《灵枢·邪客篇》说：“心是五脏六腑的大主宰，它的脏器坚固，邪气不能容纳，若邪气侵入则心受伤，心伤则神志离去而死亡。所以凡是邪气侵犯心脏的，都侵犯心之包络。”包络，指的是包裹心脏的膜。如果它无形，所指的是什么东西呢？由此可见，包络和三焦是有形的，这一点不用辩论就很明白了。
按语：手厥阴心包络，就是包裹心脏的脂膜，西医称之为心脏外面的夹膜。这层膜分为内外两层，外层厚且坚实致密，上面包裹着总回管（静脉）和动脉，下面与膈膜的上层粘连；内层外侧连接外层，内侧粘连心脏。其脉络与膈肌的血管、肺的气管和食管相通，并贯通于脑神经。心脏的脉络也从心包络发出，以通达全身。所以经文说膻中（心包络）是“臣使之官”。手少阳三焦，是水中之阳，称为相火。经文说“少阳属肾”，是指归属于肾中的命门。命门即肾系，从肾系下方生出脂膜，作为三焦的根本。这就是西医所说的腹包膜、腹腔内脏器的统膜。这层膜的起源在于肾系，向下包裹膀胱，连通两肾，包裹大小肠及女子的子宫，经过直肠的反折处，从尾骨后方上行至腹壁膜，向前到达肝脏上方、膈膜下方，转向腹部前方，包裹肝脏、裹住胃，上层与膈膜的下层粘连。膈膜的上层与心包络的下层相连，气脉贯通于肝脏下方、胃的上方，又横向生出一层薄膜，用来隔开肝和胃，这就是肝胃连膜。心肺在这层膜之上，不能被包裹，所包裹的各脏腑在肚腹之前形成一个空囊，由肝胃连膜向后有一个孔相通，透入这个空囊，名叫空窍。凡是在膈膜以下的各脏腑之间，都有这种几层膜的折叠筋带，用来系联脏腑，固定它们的位置，并保护各处运行的血管和神经，还分支生出薄膜，纵横网罗，由此脏行于彼脏，以通行气血。凡是各种连接的网膜和脂肪，都是三焦所属之物。心包络的脉络，下行穿过膈肌，依次联络三焦的上下部分，粘连延续其气；并且出于肾脏，一支游行于上、中、下三焦，各有归属的部署；另一支进入心包络，成为君主之心的辅佐。三焦起始于第七节脊椎之间，藏有水中的真火，是相火的宅舍；心包络是相火的脏，三焦是相火的腑。心包络和三焦的气化流行，都是相火的流行。用类似脏的小囊（心包络）配合同类腑的大囊（三焦），也是天地自然形成的道理，不容随意妄议。如果拘泥执着于“无形”的说法，就错了。
Chapter 25 states: There are twelve meridians, but the five zang organs and six fu organs total only eleven. Which meridian is the extra one?
The answer is: The extra meridian refers to the independent meridians of the Hand-Shaoyin (Heart) and the Heart Master (Pericardium). The Pericardium and the Sanjiao (Triple Burner) are exterior-interior partners; although they have names, they appear to lack fixed form, hence it is said there are twelve meridians.
The meaning of this question-and-answer section is that while the five zang and six fu organs correspond to the yin and yang of the hands and feet, they actually account for only eleven meridians. The additional one consists of the Hand-Shaoyin Heart meridian and the Hand-Jueyin Pericardium meridian. Both meridians belong to the Heart's vascular system. The Shaoyin meridian combines with the Taiyang Small Intestine meridian as an exterior-interior pair, and the Jueyin Pericardium meridian combines with the Shaoyang Sanjiao meridian as another exterior-interior pair. Together, these pairs constitute the twelve meridians. When the text states that the Pericardium and Sanjiao are "formless," it refers to their qi aspect, yet this phrasing is arguably imprecise. *Ling Shu · Ben Cang* states: "Those with fine skin texture and thick skin have thick Sanjiao and Bladder membranes; those with coarse skin texture and thin skin have thin Sanjiao and Bladder membranes." If the Sanjiao were truly formless, how could there be corresponding variations in thickness? *Ling Shu · Xie Ke* states: "The Heart is the great master of the five zang and six fu organs. Its organ is solid, and pathogenic factors cannot reside within it. If they do, the Heart is injured, the Shen (Spirit) departs, and death ensues. Therefore, any pathogenic factor affecting the Heart actually affects the Pericardium of the Heart." The Pericardium refers to the membrane wrapping the Heart. If it were formless, what object would it refer to? Thus, the tangible nature of the Pericardium and Sanjiao is self-evident without need for debate.
Commentary: The Hand-Jueyin Pericardium is the fatty membrane enveloping the Heart, which Western medicine identifies as the pericardial sac or epicardial fat. This membrane consists of two layers: the outer layer is thick, firm, and dense, enclosing the superior vena cava and aorta inferiorly adhering to the upper layer of the diaphragm; the inner layer connects externally to the outer layer and adheres internally to the Heart. Its vessels connect with the diaphragmatic vasculature, pulmonary airways, and esophagus, extending through to the brain nerves. Cardiac vessels also originate from the Pericardium to distribute throughout the body. Hence, the classic text describes Danzhong (the Pericardium) as the "Official of the Envoy." The Hand-Shaoyang Sanjiao represents Yang within Water, known as Ministerial Fire. The statement "Shaoyang belongs to the Kidney" implies its connection to the Mingmen (Gate of Life) within the Kidneys. The Mingmen corresponds to the renal pedicle; from below the renal pedicle, fatty tissue emerges as the root of the Sanjiao. This corresponds to the Western anatomical concept of the peritoneum and the mesenteries unifying abdominal viscera. The origin of this membrane lies in the renal pedicle, extending downward to enclose the bladder, connecting both kidneys, enveloping the intestines and the uterus in females. It passes through the rectal fold, ascends posterior to the coccyx along the abdominal wall, reaches above the liver and below the diaphragm, turns anteriorly to wrap the liver and stomach, and adheres superiorly to the lower layer of the diaphragm. The upper layer of the diaphragm connects with the lower layer of the Pericardium, allowing qi and vessels to pass between the lower liver and upper stomach. A horizontal membranous layer extends laterally to separate the liver and stomach, known as the hepatogastric ligament. The Heart and Lungs lie above this membrane and are not enclosed by it. The enclosed viscera form a hollow sac anterior to the abdomen, connected posteriorly via a hole in the hepatogastric ligament into this cavity, termed the "empty aperture." Between the viscera below the diaphragm, multiple folded membranous bands suspend and fix the organs in position, protecting blood vessels and nerves, while branching membranes weave longitudinally and transversely to facilitate qi and blood flow between organs. All such connecting omenta and adipose tissues belong to the Sanjiao. The Pericardium meridian descends through the diaphragm, sequentially linking the upper, middle, and lower Sanjiao, and adhering to their qi. It originates from the Kidney, with one branch circulating through the three jiaos to specific destinations, and another entering the Pericardium to serve as the assistant to the Sovereign Heart. The Sanjiao begins at the level of the seventh vertebral segment, storing the true fire within water, serving as the residence of Ministerial Fire. The Pericardium is the zang organ of Ministerial Fire, and the Sanjiao is its corresponding fu organ. The qi transformation and circulation of both are manifestations of Ministerial Fire. The pairing of the small sac resembling a zang organ (Pericardium) with the large sac resembling a fu organ (Sanjiao) follows natural principles and should not be subject to arbitrary speculation. To rigidly adhere to the notion that they are "formless" is erroneous.