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The human body has nine orifices: seven upper orifices and two lower orifices. The upper orifices belong to Yang, and the lower orifices belong to Yin; this is known to everyone. However, the profound truth regarding the generation and completion involving Yin-Yang, odd numbers, and even numbers was not explicitly stated in the *Huangdi Neijing* (Yellow Emperor's Inner Canon). Here, it is specifically supplemented and discussed.

Yang orifices paradoxically use even numbers, while Yin orifices paradoxically use odd numbers.

The upper orifices are collectively categorized as Yang. The ears and eyes are used for hearing and seeing; their Qi is clear and thus belongs to Yang. The nose is used for smelling, and the mouth for eating; their Qi is turbid and thus belongs to Yin.

The ear hears formless sounds, representing the utmost Yang within the upper Yang orifices. It is hollow in the middle, vertically shaped, with the two openings far apart.

The eye sees colored forms, representing Yin within the upper Yang orifices. It is solid in the middle, horizontally shaped, with the two openings relatively close together.

The nose smells formless air, representing Yang within the upper Yin orifices. It is hollow and vertically shaped. Although there are two openings, they are externally unified into one.

The mouth consumes the five flavors of food, representing Yin within the upper Yin orifices. It is both hollow and solid internally, having both excretion and intake, and is horizontally shaped. Externally it appears as one orifice, but internally it consists of two parts.

Observing the upper orifices as a whole: Yang is oblique/side-oriented, while Yin is upright/central, akin to Earth occupying the central position. Yang is vertical, and Yin is horizontal. Vertical movement governs Qi, while horizontal movement governs Blood. Blood is Yin, and Qi is Yang.

Although it is said there are seven orifices, there are actually eight. The Yang orifices are external Yang (the number 7, an odd number) and internal Yin (the number 8, an even number); external is odd, internal is even. Yang is born from 7 and completed by 8.

Generation numbers are Yang; completion numbers are Yin. The Yang orifices utilize completion numbers, which are 7 and 8.

The anterior orifice of the lower region possesses the function of generation and transformation, representing Yang within Yin. Although it has one external opening, it actually has two internal structures, thus utilizing an even number.

The posterior orifice is solely responsible for expelling turbidity, representing the utmost Yin within Yin. Both its interior and exterior consist of a single opening, thus utilizing an odd number.

Observing the lower orifices as a whole: although it is said there are two orifices, secretly there are three.

The Yin orifices are external Yin (the number 2, an even number) and internal Yang (the number 3, an odd number); external is even, internal is odd. The Yin orifices utilize generation numbers, which are 2 and 3.

For the upper orifices, the manifest number is 7 (Yang); the hidden number is 8 (Yin).

For the lower orifices, the manifest number is 2 (Yin); the hidden number is 3 (Yang).

Considering both upper and lower orifices together: the manifest total is 9, and the hidden total is 11. Eleven reduces to one. Nine represents the Old Yang, and One represents the Young Yang. When Old is completed, Young is generated.

Nine is the end of the Yang numbers, and One is the beginning of the Yang numbers. Beginning and end, upper and lower, constitute the cycle of Yang Qi.

The function of opening the orifices is to circulate Yang Qi. The profound truths are infinite, ultimately summarized by the character "Hu" (Mutual Interchange/Mutuality).

However, the mutual interchange within mutual interchange is the most difficult to comprehend. I have often sighed: For those cultivating themselves, the character "Shi" (This/Is) is difficult; for those investigating things to extend knowledge, the character "Hu" (Mutual) is difficult.