十二经络之表里。特以隧道之故。举其并行互络者而言。初不以职列也。人之阴阳皆起于足。故足之六经地分阔。
而职司要所。主一身之间。唯足六经也。手六经则地分狭。所行两臂头面之间。其两臂常动。头面肉坚风寒之所不得入。
故仲景条贯伤寒。止拈足六经。而无外伤手经之条。正以手经之所合。皆在足六经之中。非谓其不与于斯也。请申之。
太阳之经起于足。上于巅脑。以及额颅内。下于膺。中包心肺。皆太阳经也。太阳居六阳之盛。故为巨阳。而为诸阳主
气。然以同冲气起于少阴。乃以其阳而借纳膀胱。其下膺中者。少阴心。太阴肺。一君一相。并居其间。而肺主皮毛。
心部于表。皆与太阳合。是以寒邪一犯太阳。遂伤肺及心。以犯皮毛血脉。为心肺之所合。若皮毛凛栗。鼻塞声重畏寒
无汗。以及心烦。皆太阳症。而心肺为之变。仲景设麻黄汤发汗疏肺。桂枝汤和表止烦宁心。岂非发太阳即发手太阴少
阴耶。是手之太阴少阴，已兼于足太阳之一经矣。若手太阳小肠经者。其气用岂能及足。特以与心络并行隧道。表里又
与足太阳连经。故亦以三阳归之。非曰其职能与足太阳并列也。后学亦察一拈太阳。使以小肠与膀胱双举。岂知要者哉。
足阳明自额颅而下绕夹鼻。口下人迎。下乳内廉。下挟脐。其脉齐太阳。皆五道。至气街中属胃络脾。凡面之全部。膺
胸与腹内外。至足胫外廉。皆阳明也。经为两阳合明。合明者。太阳少阳共明于此也。其经气盛血多热甚。其地位阔。
其职司要。又主中部谷神之所升。皆卫之所出。若大肠者。为胃化物之器。受盛之官。其络与足阳明接。经故亦谓之手
阳明。亦非谓其能有阳明之职事也。故大肠小肠之经。即同于胃。其病与否。皆与胃同。而初无与于肺心。若经络自病
延及肺心。亦止在经络。不若伤寒之传经也。足少阳胆之经。由耳颊下胁。下膝外廉。居身之两侧。称身后之太阳。身
前之阳明。接壤密布于内。为半表里。故少阳居之。为阳明之次。皆以地分形层分职言也。其经与职游行三焦。摄于心
胞。心胞三焦。总同一职。此无复手少阳手厥阴之别矣。三阴正位。唯足太阴脾。为六经之所主。心地德居中而主里。
若太阴肺。以其朝百脉主元气故亦有太阴之名。其实为阳中之少阴。初非居三阴之职。而分太阴脾位之司也。三阴之正。
惟少阴肾。能正位于坎。配心之离。而心为太阳。故肾亦名阴中之太阴。其实天之少阴从火。人之少阴从水。此少阴心。
不夺少阴肾之用也。一阴本厥阴肝。其经胞络亦与并称。然心胞本非交尽之厥。以经相接。故亦名之。心胞则相火。厥
阴则风木。所不得混列也总之风寒邪之入三阴者。皆在足三阴。而病在手三阴者。皆在足三阳。故风寒之入与传。止有
足六经。而无用手六经。即人身三阴三阳之正病。亦断不以经络手足并拈。凡以为是也。
The exterior-interior relationship of the twelve meridians is merely named so because they run parallel and interconnect within the body's tunnels; initially, this was not based on functional classification. The Yin and Yang Qi of humans all originate from the feet. Therefore, the six Foot Meridians have a broad distribution area, their functions are crucial, and they govern the whole body—only the six Foot Meridians do this. The six Hand Meridians have a narrow distribution area, traveling only between the two arms and the head and face. Since the arms are in constant motion and the flesh of the head and face is firm, Wind-Cold pathogens cannot enter. Thus, when Zhang Zhongjing organized the syndromes of Cold Damage (Shanghan), he only selected the six Foot Meridians and did not include clauses regarding external injuries affecting the Hand Meridians. This is precisely because the functions associated with the Hand Meridians are already contained within the six Foot Meridians; it does not mean that the Hand Meridians are excluded from this system. Let me elaborate further.
The Foot Taiyang Bladder Meridian originates in the foot, ascends to the vertex and brain, reaches the forehead and cranial interior, descends to the chest, and envelops the Heart and Lungs internally—all these areas fall under the Foot Taiyang Meridian. Taiyang holds the most vigorous position among the six Yang Meridians, hence it is called "Ju Yang" (Giant Yang) and serves as the master Qi of all Yang Meridians. However, the Chong Mai (Penetrating Vessel) Qi originates from Shaoyin Kidney and, borrowing the Yang of Taiyang, enters the Bladder. In the chest region, there are the Shaoyin Heart and the Taiyin Lung, one representing Ministerial Fire and the other Sovereign Fire, residing together there. The Lung governs the skin and hair, and the Heart distributes to the exterior; both combine with the Taiyang Meridian. Therefore, when Cold Evil invades the Taiyang Meridian, it subsequently injures the Lung and the Heart, because invading the skin and blood vessels affects the organs combined with them. Symptoms such as shivering of the skin and hair, nasal congestion with heavy voice, aversion to cold, absence of sweating, and mental restlessness are all symptoms of Taiyang disease, yet they represent changes in the Heart and Lung. Zhang Zhongjing established Mahuang Tang (Ephedra Decoction) to induce sweating and disperse the Lung, and Guizhi Tang (Cinnamon Twig Decoction) to harmonize the exterior, stop restlessness, and calm the Heart. Is this not treating the Taiyang Meridian, which is equivalent to treating the Hand Taiyin Lung Meridian and Hand Shaoyin Heart Meridian? Thus, the functions of the Hand Taiyin and Hand Shaoyin are already integrated into the single Foot Taiyang Meridian. As for the Hand Taiyang Small Intestine Meridian, how could its Qi function reach the feet? It is merely because it runs parallel with the Heart Collateral in the tunnel, and its exterior-interior relationship connects with the Foot Taiyang Meridian, so it is also categorized under the Three Yang Meridians. This does not imply that its function is equal to that of the Foot Taiyang Meridian. If later students fail to observe this key point and list the Small Intestine alongside the Bladder, they miss the essence.
The Foot Yangming Stomach Meridian descends from the forehead, wraps around the nose, passes through the Renying point below the mouth, descends along the inner aspect of the breast, goes down flanking the navel. Its pulse pathways are similar to Taiyang, totaling five routes, reaching the Qichuan point where it belongs to the Stomach and connects to the Spleen. All areas of the face, the anterior chest and abdomen (inside and out), down to the lateral aspect of the lower leg, belong to the Yangming Meridian. The meridian is called "Two Yangs Combined Brightness" (Liang Yang He Ming), meaning the brightness of Taiyang and Shaoyang converges here. Its Qi is vigorous, blood is abundant, and heat is intense. Its geographical scope is broad, and its critical function governs the ascent of Grain Spirit (Gu Shen) in the middle jiao, from which Wei Qi (Defensive Qi) emerges. The Large Intestine is the vessel for the Stomach's transformation of food, an official of reception and storage. Its collateral connects with the Foot Yangming, so the text also refers to it as the Hand Yangming. This does not mean it possesses the functions of the Yangming Meridian. Therefore, the meridians of the Large and Small Intestines are equated with the Stomach; whether diseased or not, they align with the Stomach, initially having no direct involvement with the Lung and Heart. If pathology spreads from the meridians themselves to the Lung and Heart, it remains within the meridians, unlike the transmission of meridians in Cold Damage.
The Foot Shaoyang Gallbladder Meridian travels from the cheek and ear down to the hypochondrium, descends to the lateral aspect of the knee, located on both sides of the body. It is called the Taiyang behind the body and the Yangming in front of the body, densely interlacing internally, occupying the semi-exterior-semi-interior position. Thus, the Shaoyang Meridian resides here, secondary to Yangming. This classification is based on geographical distribution and anatomical layers. Its meridian Qi and functions travel through the Sanjiao (Triple Burner) and regulate the Pericardium. The Pericardium and Sanjiao share the same overall function, eliminating the distinction between Hand Shaoyang Sanjiao and Hand Jueyin Pericardium.
Among the Three Yin Meridians, the true position belongs only to the Foot Taiyin Spleen, which governs the six meridians. The Earth element virtue centers and governs the interior. As for the Taiyin Lung, although it has the name Taiyin because it meets all vessels and governs Yuan Qi, it is actually Shaoyin within Yang, and initially does not hold the function of the Three Yin Meridians nor share the jurisdiction of the Foot Taiyin Spleen. The true position among the Three Yin Meridians belongs only to the Shaoyin Kidney, which can correctly reside in the Kan position, matching the Li position of the Heart. Since the Heart is Taiyang, the Kidney is also named Taiyin within Yin. In reality, Heaven's Shaoyin follows Fire, while Human Shaoyin follows Water. This ensures that the Shaoyin Heart does not usurp the function of the Shaoyin Kidney. The One Yin is originally the Jueyin Liver, and its meridian, the Pericardium Collateral, is also mentioned together. However, the Pericardium is not truly Jueyin (extreme Yin); due to meridian connection, it is given this name. The Pericardium relates to Ministerial Fire, while Jueyin relates to Wind-Wood; they cannot be confused or listed together. In summary, when Wind-Cold pathogens invade the Three Yin, it is always the Foot Three Yin; when diseases manifest in the Hand Three Yin, it is actually due to the Foot Three Yang. Therefore, the invasion and transmission of Wind-Cold involve only the six Foot Meridians, not the six Hand Meridians. Even for the true diseases of the Three Yin and Three Yang in the human body, one should never simultaneously cite Hand and Foot meridians. Any view suggesting otherwise is incorrect.