The pineal gland, the third eye, the seat of the soul, the Ajna Chakra.
The pineal gland is a small endocrine gland in the brain. It is located near the center of the brain, between the two hemispheres.
Descartes believed the pineal gland was the “seat of the soul”.
The pineal gland is believed to be the biological locus of spiritual experience (see the work of Dr. Rick Strassman, DMT: The Spirit Molecule) and is alleged to be highly “activated” when people obtain mystical states.
The pineal gland appears in the human fetus at around 49 days of gestational development.
Interestingly enough, Tibetan Buddhists believe that 49 days is the amount of time it requires for one soul to incarnate into the next. Furthermore, the differentiation of the fetus into male or female also occurs at the 49 day mark.