"The predominating module of the composition of human body is eight and many lines on the drawing coincide with the lines of the modular plain. The figure in the form of the letter Thau embraces 22 squares of the composition, whereas on each half remains 21 or 3 x 7 squares. 22 and 7 are connected through the rational approximation of p = 22/7.
Number 22 also invokes the total number of Hebrew alefbeth, and numbers 3, 7, and 12 (= 22-3-7) are the numbers of divisions of Hebrew alefbeth into three groups described in Sepher Yetzirah - The Book of Formation, a fundamental kabbalistic treatise on the nature of letters and words, suspected to originate from 13th century. The 32 Paths of Wisdom described in Sepher Yetzirah comprise 10 Sephiroth and 22 Letters. 32 Paths are written in the circumference of the modular square 8x4 = 32. The figure is positioned in the shape of T(hau), the 22nd, last letter of alefbeth. The Tetraktys and the kabbalistic Tree of Life are comparable glyphs, both comprising the ten spheres.
Vitruvius is reporting that the navel is the exact center of the human body. The circle on Leonardo's drawing has it's center in the navel, but if the figure is 'squared' the center becomes the phallos which is, concerning this drawing from the compositional point of view, more important, since it is the center of the underlying geometry that outlines the basic features of the figure.
The most fundamental composition consists of a circle, a square, and a triangle, a sigillum known to magicians and alchemist, sometimes called the Universal Seal of Light or the Seal of Hermes. The compositional triangle on this drawing is concealed, even though that it outlines important segments. It is drawn in the circle within the square and it coincides with the progression of squares as depicted on the illustration."

Leonardo Da Vinci