Harderian gland

{{Short description|Gland in the eye socket of tetrapods}}

File:Cave vertebrates of America; a study in degenerative evolution (1909) (20577823892).jpg; the Harderian gland is marked H. gl. in diagram B (horizontal section of head) and C (horizontal section through right eye).]]

The Harderian gland is a gland found within the eye's orbit that occurs in tetrapods (reptiles, amphibians, birds and mammals) that possess a nictitating membrane.{{cite journal |author=Payne AP |title=The harderian gland: a tercentennial review |journal=Journal of Anatomy |volume=185 |issue=1 |pages=1–49 |date=August 1994 |pmid=7559104 |pmc=1166813}}

The gland can be compound tubular or compound tubuloalveolar, and the fluid it secretes (mucous, serous or lipid) varies between different groups of animals. In some animals, it acts as an accessory to the lacrimal gland, secreting fluid that eases movement of the nictitating membrane. Research has proposed that the gland has several other functions, including that of a photoprotective organ, a location of immune response, a source of thermoregulatory lipids, a source of pheromones, and a site of osmoregulation. In mammals, the gland secretes an oily substance used to preen the fur. The presence or absence of this gland is one of the cues used by palaeontologists to determine when fur evolved in the ancestors of mammals.{{cite journal |doi=10.1668/0003-1569(2000)040[0585:SFAWTO]2.0.CO;2 |year=2000 |volume=40 |issue=4 |pages=585–96 |title=Selective Factors Associated with the Origin of Fur and Feathers |journal=American Zoologist |last1=Ruben |first1=John A. |last2=Jones |first2=Terry D.}}

The Harderian gland was first described in 1694 by Swiss anatomist Johann Jacob Harder (1656–1711). He documented his findings in a paper titled Glandula nova lachrymalis una cum ductu excretorio in cervis et damis,{{cite journal |doi=10.1016/S1542-0124(12)70307-5 |pmid=19635245 |title=Tear Apparatus of Animals: Do They Weep? |journal=The Ocular Surface |volume=7 |issue=3 |pages=121–7 |year=2009 |last1=Murube |first1=Juan}} ("A new lachrymal gland with an excretory duct in red and fallow deer", English translation).{{cite journal |vauthors=Hillenius WJ, Phillips DA, Rehorek SJ |title='A new lachrymal gland with an excretory duct in red and fallow deer' by Johann Jacob Harder (1694): English translation and historical perspective |journal=Annals of Anatomy |volume=189 |issue=5 |pages=423–33 |year=2007 |pmid=17910396 |doi=10.1016/j.aanat.2006.10.008}}