Pineal body is an endocrine gland which secretes melatonin hormone. Pineal body or gland is present in groove between cerebrum and cerebellum and vestigial of 3rd eye in man. Pineal gland contains light sensitive cells or has nervous connections from the eyes and melatonin regulates function related to light, so it regulates biological clock of body. It also regulates sexual behaviour and the period of puberty.