The middle joint of the finger is the "finger stomach". In taiji practice this "stomach" is extended, is peng, is stretched out and strong.
This stretching of the finger stomach is coincidental with formation of the "tiger's mouth". The "tiger's mouth" is the part of the hand that is found between the thumb and the first finger as they stretch, open and close simultaneously to create a circular rounded peng that can be used to grab or hold. The "tiger's mouth" is open and closed at once. One should be able to feel the energy in this space.
The small finger and the thumb reach toward each other, and away at the same time--open and closed at once. The hand in total is shaped like a "roof tile" (look for images of Chinese roof tiles that are flatly rounded in form).
September 30, 2014