" Never two without three "

binocular vision of man is one of the most perfected in the animal world. Yet the 2-eye system may not have always guided human sight. Like all vertebrates, we have an epiphysis or pineal gland located between the two hemispheres of the brain which is the size of a pea .
According to some scholars, this epiphysis is all that remains of the third eye of our distant aquatic ancestors which would have calcified. It is possible that this useless third eye has acquired secretory functions over time. This gland secretes hormones regulating circadian rhythms (biological clock).
This third eye still exists in some animals. This epiphysis grows forward to form a median, single eye in the case of the shark or batrachians. In the lizard, it is a perfected eye with 5 layers of retinal cells and a macula.
Besides these biological notions, the third eye has an esoteric dimension. It is found in many Eastern civilizations (Buddhist, Taoist…), it is the psychic center other organs and allow meditation.

For Descartes, in the 17th century, it is "the seat of the soul"