The Rishis of India had without doubt a wealth of encyclopedic knowledge, they devised Hatha yogasana to perfect the Gunas (The fundamental nature of Humans) in order to maintain good health. The three gunas are Rajas (dynamism), Tamas (inertia) and Sattva (equilibrium of truth). The path of a yogi is to balance the three gunas and to live predominantly in a state of Sattva.

The Zodiac, Head to Toe. What follows is a very brief description of the zodiacal associations for parts of the body. 

Aries rules the head and all of its contents (brain, skull, etc)

Taurus rules the throat and also the thyroid gland.

Gemini rules shoulders, arms and hands and the nervous system; it's associated with the lungs and breathing (and is the first air sign in the zodiac).

Cancer rules the breasts, the stomach and alimentary canal.  Cancer is also the first water sign linking it with the realm of emotions and intuition.

Leo rules the back and the spine,  Leo’s ruler the Sun, rules the heart, appropriately it is associated with love, romance and a sunny disposition.

Virgo rules the belly and the digestive tract, the small and large intestines, colon and rectum.  Virgos are highly conscious of dirt and disorder.

Libra rules the hips and, the kidneys. The hips are like a scale inside our body from which right and left legs dangle, balancing us as we walk.

Scorpio rules the genitals, whether male or female and also, paradoxically, the nose.

Sagittarius rules the buttocks and thighs. These major muscle groups of the body are the parts most involved in locomotion, and Sagittarius is the sign of travel and exploration.  Through its ruler Jupiter, Sagittarius also rules the liver.

Capricorn is all about structure and thus rules the skeleton with all its bones, including the teeth and the knees.  The skeleton is the framework on which the body is built. The skin is ruled by Capricorn too: implying boundaries and structure. 

Aquarius rules the ankles, and all the joints.  Aquarius is all about networking and connecting. 

Pisces rules the feet, a body part which is both humble and sensitive.  The feet are a homunculus, "little man" and Pisces is generally regarded as a repository for the qualities of all the signs that came before (thus the Piscean tendency towards the dispersion of identity).