PARIETAL EYE Meaning and
Definition
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Parietal eye, also known as the third eye or pineal eye, is a specialized and primitive sense organ found in certain vertebrates, primarily reptiles and amphibians. It is typically located at the top of the head, in the middle of the parietal bone, hence the name parietal eye. This unique organ possesses a distinct photoreceptive structure and a rudimentary lens, although its function is still not entirely understood.
The parietal eye is believed to play a role in regulating various physiological functions, especially in response to light and dark cycles. It is connected to the pineal gland, a hormone-secreting gland involved in regulating body rhythms such as sleep and reproduction. The parietal eye's ability to detect light intensity and changes in environmental conditions may assist in determining time of day, duration of light exposure, and adjusting behavior and physiology accordingly.
Unlike the paired lateral eyes, which provide binocular vision, the parietal eye is a single ocular structure that can perceive light independently. It typically possesses limited visual acuity and is sensitive to certain wavelengths of light, particularly in the ultraviolet range. In some reptiles, such as lizards and tuataras, the parietal eye is visible as a translucent spot covered by a specialized scale or plate.
In summary, the parietal eye is an evolutionary remnant of a previously functional eye structure that provides sensory information related to light and darkness, likely influencing the regulation of biological rhythms and behavior in reptiles and certain amphibians.
Etymology of PARIETAL EYE
The word "parietal" originates from the Latin word "parietalis", which means "relating to a wall" or "on the side". It is derived from the Latin word "paries", meaning "wall".
The term "parietal eye" refers to the third eye found in certain reptiles and amphibians on the upper surface of their skull, specifically on the parietal bone. The term "parietal" is used to describe the location of this eye on the side of the skull. Hence, the etymology of the term "parietal eye" combines the Latin word "parietalis" with "eye" to describe the anatomical structure.
