UNIFIED Field of Consciousness (Descartes’ Sens Communs)
The organ is (normally) unpaired and connected by a stalk to the pineal body that lies central in the brain. It has no muscles to control direction, no eyelid allowing it to be closed, and no iris allowing it to focus. The eye varies in complexity from a simple sac-like vesicle to the well-developed structures found in sphenodon and certain lacertilians, with a lens, retina, rods and cones, a fluid-filled space corresponding to the humours of lateral eyes, and a nerve that transmits impulses to the brain.... in fact all the components of lateral eyes except an iris sphincter and orbital musculature.
Experiments on young E-2 sphenodon, covering their median eyes, have confirmed that the organ has a wide range of functions. The pineal eye seems necessary to detect the presence of predators. It assists in temperature regulation, and informing when to bask in the sun and when to move to shade. It has a role in changing the skin colour according to prevailing conditions of light, particularly by exuding melatonin like substances that affect pigmentation variation occurring between day and night. Changes in the season are detected by noting variations in radiation emitted by the sun. Such information is particularly important to determine breeding time.
As the main collector and communicator of sense-information from the external environment, and having existed millions of years before auditory and lateral-visual systems, the median eye was seemingly the ‘interface’ and receptacle in which any ‘awareness’ that primitive creatures had of things and events outside of its body. It could be described as a "spotlight of consciousness," or as I would contend, a "physical site of mind".