There are 12 primary channels run vertically, bilaterally and symmetrically.
The 3 yin channels of the hand are Lung, Pericardium, and Heart - begin on the chest and travel along the inner surface of the arm to the hand.
The 3 yang channels of the hand are Large Intestine, San Jiao and Small Intestine - begin on the hand and travel along the outer surface of the arm to the head.
The 3 yang channels of the foot are Stomach, Gallbladder, and Bladder- begin on the face, in the region of the eye, and travel down the body and along the outer surface of the leg to the foot.
The 3 yin channels of the foot are Spleen, Liver and Kidney- begin of the foot and travel along the inner surface (mostly posterior and medial portion) of the leg to the chest or flank.
The external pathway is what is normally shown on an acupuncture chart and it is relatively superficial.
All the acupuncture points of a channel lie on its external pathway.
The internal pathways are the deep course of the channel where it enters the body cavities and related Zang-Fu organs.
The superficial pathways of the 12 channels describe 3 complete circuits of the body.
The flow of energy through the meridians is as follows:
Lung channel of hand taiyin to Large Intestine channel of hand yangming to Stomach channel of foot yangming to Spleen channel of foot taiyin to Heart channel of hand shaoyin to Small Intestine channel of hand taiyang to Bladder channel of foot taiyang to Kidney channel of foot shaoyin to Pericardium channel of hand jueyin to San Jiao channel of hand shaoyang to Gallbladder channel of foot shaoyang to Liver channel of foot jueyin then back to the Lung channel of hand taiyin