The Structure and Functions of Harderian Gland

The Harderian gland is an orbital gland, as seen in a majority of terrestrial vertebrates. The gland was first distinguished by Johann Jacob Harder in two deer species in 1694. The mammalian Harderian gland is located within the interior angle of the eye, in association with the third eyelid and its secretory duct opens at the surface of nictitans membrane. The lumen of avian Harderian gland, compounding tubular and tubuloalveolar structures, is surrounded by the columnar epithelial cells in varying heights. Plasma cells are situated in the subepithelial region of the gland. The Harderian gland is generally located medially or medioventrally of the eyeball in reptiles. This gland is the unique (sole) eye gland in snakes. Inter‐species differentiation of the Harderian gland’s morphological and biochemical properties are astonishing, and the reason of this differentiation was thought to provide the requirement of adaptation to the terrestrial life through the evolving functions. Additionally, some researchers have also revealed the presence of gland in primates, in recent years. Therefore, the aim of this review was to evaluate the structure and function of Harderian gland, as having various and important properties in different species.