abnormal gland physiology abnormal Harderian gland physiology MP:0003859 MPheno.ontology The Harderian gland does not normally exist in some types of mammals (bats, cows and horses), terrestrial carnivores, and higher primates including human. any functional anomaly of the retroocular sebaceous gland found within the orbit of mammals that possess a nictitating membrane (third eyelid); the chief products of the gland vary between different groups of vertebrates, and epithelial cells possess granules or vacuoles whose contents may be mucous, serous or lipid; in rodents, the Harderian gland is especially large and secretes lipids (by a merocrine mechanism), melatonin and porphyrins; ascribed functions include a role in lubrication and protection for the eyeball and nictitating membrane (by lipids), photoprotection (by porphyrin), photoreception (by regulation of the incidence of light on the retina), and thermoregulation (in some rodents)