The body is divided into three parts and nine sections. The three parts are the spine, the two arms and the two legs. 1. Spine: the head, thorax and abdomen. These three sections make up the main trunk of the body.
2. Arms: the hands, elbows and shoulders. These three sections constitute the upper limbs.
3. Legs: the hips, knees and feet. These three sections constitute the body's lower limbs. So the body is divided into upper, middle and lower vessels. The upper is from the chest and arms upwards, the middle constitutes waist and hips, and the lower vessel is from the thighs and knees downwards.

Wu Family T'ai Chi Ch'uan (1980)