Harderian gland

In some animals, it acts as an accessory to the lacrimal gland, secreting fluid that eases movement of the nictitating membrane.

[1] 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.

[2] 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,[3] ("A new lachrymal gland with an excretory duct in red and fallow deer", English translation).