Pineal gland, the mystical third eye

Pineal gland 

It is a very small unpaired midline brain structure of endocrine gland, tiny as a rice grain size, situated laterally (anatomically asymmetrical) in the epithalamus, between two hemisphere, near the center of the brain, but devoid of blood-brain barrier (so having profuse blood flow, second only to kidney), well referred as pineal body, pineal word came as due its resemblance of a pine cone or pine apple shape.

Role of pineal gland

It has a role of maintaining circadian rhythm (are physical, mental, behavioral changes that follows a 24-hour cycle) and seasonal cycle in the body. When eyes are not stimulated with light (signals from retina of lightning environment), Serotonin neurotransmitter is converted to a hormone Melatonin to initiate sleep cycle by this tiny gland. That way Melatonin is called sleep hormone, whose secretion level is highest in the middle of the night.

Function

Due to it's resemblance of Parietal eye & the Photoreceptor cell in lower animal kingdom, it could phylogenetically regarded as vestigial remnant. 

Biomolecules Serotonin and Melatonin are structural analogies to DMT (dimethyltryptamine) released in REM phase, responsible for visualization of images and dreams, where a travel through time & space dimension occurs. DMT is most powerful hallucinogen found in naturally.

In the immediate state before death, large amount of DMT is produced.

As this endocrine gland/body, secreting Melatonin/DMT, works on similar pattern of our external eye being a photoreceptor in nature, seems an ancestral Parietal eye, vestigial to us, but still doing a powerful chemical production site which maintains circadian rhythm and a balance between wakefulness & sleep cycles. Many a time this has been referred as mythical Third eye, this is a door between our known to the unknown world. Due to the small size, it is most delayed discovered endocrine gland and still remains less understood, seems to many a mystical due to it's role in higher realm transcendental spiritual perception, perhaps due to triggering on of DMT production by controlled meditation or such willful activity by humans, as it receives the Sympathetic innervation from superior cervical ganglion.

Clinical aspects

Excessive calcification of Pineal gland disrupts its function. Aging is another reason of reduced Melatonin level causing disruptive sleep cycle.