The system of meridians is mainly composed of the twelve regular meridians, twelve meridian branches, fifteen collaterals, twelve meridian tendons, twelve skin areas and eight extraordinary vessels .
    The twelve meridians are the trunk parts of the meridian system and "are connected with the viscera internally and limbs and skeleton externally" to transport qi and blood to the viscera, limbs and skeleton. The twelve meridian branches are the branches of the twelve meridians to reinforce the connection between the zang and fu organs externally and internally related and the meridians distributing over the head and face in external and internal relation. The fifteen collaterals stem from the twelve meridians and the conception and governor vessels as well as the spleen for reinforcement of the connection of the meridians with internal and external relationship on the four limbs as well as the association of the anterior, posterior and lateral parts of the trunk of the body.   
 
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