The meridian-collateral theory is concerned with the physiological functions and the pathological changes of the meridian-collateral system, and their relationships with zang-fu organs. It is an important component of the theoretical system of TCM. And it is considered as a theoretical basis of all clinical subjects of TCM, especially that of acupuncture, moxibustion, tuina and qigong. Besides, it guides the clinical practice of other branches of TCM.

The meridians and collaterals are pathways along which qi and blood circulate through the whole body. The meridians are the major trunks of the meridian-collateral system and run longitudinally within the body, while the collaterals are the branches of the meridians and are reticularly distributed over the whole body. Hence, the meridians and collaterals, connecting the zang-fu organs with extremities, the upper with the lower and the internal with ihe external portions of the body, make all the body’s organs and tissues an organic whole

The Composition of the Meridian-Collateral System

The meridian-collateral system consists of meridians and collaterals as well as their subsidiary parts. This system, internally, links the zang-fu organs and, externally, joins the tendons, museles and skin.

The meridians are classified into three categories: the regular meridians and the extra meridians and the divergent meridians. There are twelve regular meridians, namely the three yin meridians as well as the three yang meridians of the hands and feet. They are known collectively as “the twelve regular meridians”, which are the main passages for qi and blood circulation and start and terminate at given seats, run along fixed routes and meet indefinite orders. They are directly connected with the relevant zang-fu organs. The eight extra meridians are composed of Du,Ren, Chong, Dai, Yinqiao, Yangqiao, Yinwei and Yangwei meridians. They are interlated with the twelve regular meridians and perform the functions of dominating, connecting and adjusting the twelve regular meridians. And they are not directly related to the internal organs in addition, the twelve divergent meridians are the extensions of the twelve meridians. They originate from the limbs, run deeper into the zang-fu organs and emerge from the shallow neck.

Their action is to enhance the Links between every pair of meridians exteriorly-interiorly related in the twelve meridians and complement the organs and bodily areas to which the regular meridians can not get.

The collaterals are the branches of the meridians. They are divided into three groups: the divergent collaterals, superficial collaterals and tertiary collaterals. The divergent collaterals are the larger and main collaterals. The divergent collaterals originate from the twelve meridians as well as Du and Ren meridians respectively. Together with a large splenic collateral, they are altogether “fifteen divergent collaterals”. Their chief task is to strengthen the links between every pair of meridians exteriorly-interiorly related on the body surface. The superficial collaterals are ones that run through the surface layer of the human body, and often emerge on the surface. And the tertiary collaterals refer to the smallest and the thinnest ones of the whole body.

In addition, there are the subsidiary parts of the meridian system, including the twelve skin zones and twelve musculature zones. Therefore, they are the parts that connect the twelve meridians with the

superficial portions and the muscular portions of the body respectively. Considering the important place of the twelve meridians and the eight extra meridians in the meridian-collateral system. we are going to take them as the main subject for discussion.

Tab. 2 The Nomenclature and Classification of the Twelve Meridians

Tab.2 shows that every meridian consists of three parts.

) Hand or foot:

(1)手或足

The meridians starting or terminating at the hand are named “Hand”, while those starting or terminating at the foot are named “Foot”. So the twelve meridians are divided into four groups: three yin meridians of hand, three yang meridians of hand, three yin meridians of foot, and three yang-meridians of foot. Each of the meridian is named according to the medial or the lateral aspect of hand or foot, the names to which zang and fu pertain, and the nature of yin or yang.

2 ) Yin or yang:

The meridians going in the medial aspect of the limbs are named “yin”, whereas those in the lateral aspects are named “yang”. The medial aspect of the limbs is subdivided into the anterior border, midline and the posterior border. And the yin meridians running through these parts are named Taiyin,Jueyin and Shaoyin respectively. The lateral surface of the limbs is also subdivided into the anterior border, the midline and the posterior border. And yang meridians are termed “Yangming”,”Shaoyang”, and “Taiyang”.

3) Zang or fu:

The nomenclature of zang or fu is determined in the light of the nature to which zang or fu pertains. For example, the meridian pertaining to the kidney is named the kidney meridian, and the rest may be deduced by analogy.

To sum up, it is quite evident that there is no name that does not involve hand or foot, yin or yang, zang-organ or fu-organ in the twelve meridian.

Courses, Connections, Distributions, Exterior-lnterior Relations and Flowing Order of the Twelve Meridians

1. The Coursing and Connecting Law of the Twelve Meridians

The coursing and connecting law of the twelve meridians is: the three yin meridians of the hand travel from the chest to the end of the fingers where they connect with the three yang meridians of the hand; the three yang meridians of the hand go up from the end of the fingers to the head on which they connect with the three yang meridians of the foot; the three yang meridians of the foot descend from the head to the the end of toes where they join the three yin meridians of the foot; the three yin meridians of the foot ascend from the toes to the abdomen and chest in which they meet the three yin meridians of the hand. Thus, the twelve meridians are connected with each other, forming a circle like pathway along which yin and yang smoothly circulate without terminus. See the following diagram.

Fig. 5 Flowing direction and Connecting Law of the Twelve Meridians

It is clearly seen from fig. 5 that the three yang meridians of the hand terminate at the head from which the three yang meridians of the foot start. The three yang meridians of the hand and the foot meet at the head So, TCM says:”The head is the junction of all yang meridians”

2. Distributions and Exterior-Interior Relations of the Twelve Regular Meridians1) Distributions 2.

The twelve meridians are distributed symmetrically on the left and right sides of the body and run along their fixed courses. Distribution in the limbs: The medial aspect of the limbs attributes to yin, the lateral to yang. Each limb is distributed by Taiyin and Yangming meridians are on the anterior border, Shaoyin and Taiyang meridians are on the posterior border, and Jueyin and Shaoyang meridians are on the midline.

Distribution on the head and face: Yangming meridians run through the face and forehead, Taiyang meridians run through the cheek, vertex and occiput of the head and Shaoyang meridians run through both sides of the head.

Distribution in the body trunk: The three yang meridians of hand run through the scapular part. Among the three yang meridians of foot, Yangming meridians run in the front of the trunk (thoracico-abdominal aspect), Taiyang meridians along the back (the dorsal aspect) , and Shaoyang meridians along the sides. All the three yin meridians of the hand come out of the axillae without exception, all the three yin meridians of foot run along the ventral aspect. The meridians running through the ventral aspect from the medial to the lateral are, in turn, termed Foot-Shaoyin, Foot-yangming, Foot-Taiyin and Foot-Jueyin(note: as regards the medial sides of the two lower limbs, at 8cun (24cm) above the medial malleoli, Jueyin is located in theanterior, Taiyin in the middle and Shaoyin in the posterior part.)

The Exterion-Interior Relations between the Twelve Meridians

The twelve regular meridians, connected with each other by the divergent meridians and divergent collaterals, form six pairs of exterior-interior relationships. Their exterior-interior relationships are as follows: the Large Intestine Meridian of Hand-yangming and the Lung Meridian of Hand-Taiyin; the Tri-energizer Meridian of Hand-Shaoyang and the Pericardium Meridian of Hand-Jueyin; the Small intestine Meridian of Hand-Taiyang and the Heart Meridian of Hand-Shaoyin; the Stomach Meridian of Foot-yangming and the spleen Meridian of Foot-Taiyin; the Gallbladder Meridian of foot-Shaoyang and the Liver Meridian of Foot-Jueyin; and the Urinary Bladder Meridian of Foot-Taiyang and the Kidney meridian of Foot-Shaoyin. The Taiyang meridianand Shaoyin meridian of foot are exteriorly-interiorly related, and so are the Shaoyang meridian and the Jueyin meridian of foot,and the Yangming meridian and Taiyin meridian of foot. These are called the”yin and yang of foot”; while the Taiyang meridian and the Shaoyin meridian of hand are exteriorly-interiorly related, and so are the Shaoyang and the Jueyin meridians, and the Yangming and the Taiyin meridians of hand. These are called the”yin and yang of hand”.

The exterior-interior relationship of the twelve meridians not only strengthen the connection between each specific pair of meridians with exterion-interior relationship, but also promote each pair of zang-fu with the exterior-interior relationship to coordinate each other physiologically and influence each other pathologically. In treatment, acupoints of the two meridians with the exterior-interior relationship may be alternatively used.

3) The Flowing Order of the Twelve Meridians

The circulation of qi and blood inside the Twelve meridians is like the circular movement endlessly. Their circulation starts from the lung meridian of Hand-Taiyin, runs to the liver meridian.