Pineal gland

Pineal gland, pea-sized glandlike structure situated over the brain stem that appears to be a vestigial remnant of a functioning endocrine gland in other animals. It has no known function in humans, although Réné Descartes thought it to be the seat of the soul. It has a role in pigmentation in some species; calcium deposition in the pineal makes it a useful marker of midline in skull X-rays.