The Meridians is a comprehensive term of "Jingluo" in Traditional Chinese Medicine. They are the passages through which the Qi can be conducted. The meridians mainly refer to the paths of main trunks which run up and down, interiorly and exteriorly within the body. The branches of meridians are called collaterals which imply the networks, thinner and smaller than meridians, run crisscrossly over the body. The chapter, Discussion on the Measurement of Meridians(Chapter 17)in Miraculous Pivot says: "The meridians are internal trunks, its transversing branches are collaterals, the subdivisions of collaterals are minute collaterals."

The meridians and its collaterals belong to the Zang-Fu organs interiorly and extend to the extremities and joints exteriorly integrating the Zang, the Fu, tissues and organs into an organic whole, by which they transport Qi of blood and regulate Yin and Yang, keeping the functions and activities of all parts of the body in harmony and balance relatively.

The theory of the meridians deals with the courses and distributions, physiological functions, pathological changes of tile meridians of the human body, and their relations to the ZangFu organs. It guides the diagnosis and treatment for clinic of Traditional Chinese Medicine and it links tightly with the theory of acupuncture.

Development of the Theory of the Meridians
    
The theory of the meridians is formed through longtime practice and observation of Chinese people. Based on the analysis of records, the formation is as follows:
     
1. Observation of Needling Sensation: Acupuncture produces sensation of soreness, numbness, distension or heaviness. This sensation usually goes to the distal region along a definite pathway.
     
2. The Summary of the Therapeutic Effects of Acupoint: The acupoints which have similar clinical effects are regularly lined on the same course.
     
3. Reference of the Pathological Phenomenon on the Body Surface: When there appears the disorder in a certain organ, then on the corresponding areas of the body surface appear tenderness, tubercles, skin rash and changes of the skin color, this is also another way of discovering the system of meridians.
     
4. Suggestions from knowledge of Anatomy and Physiology:With the help of anatomy. Chinese doctors in ancient times got to know the position, the appearance and some physiological functions of internal organs, and observed the tunnellike and the cordlike structures are distributed over the body and connected with four limbs as well. The phenomenon of the circulation of blood can be seen in same blood vessels.