Histological Structure of Harderian Gland

Abstract

Although the harderian gland was discovered more than 300 years ago, yet it was considered as an accessory "Lacrimal Gland" for a long time until a sexual dimorphism was considered in the

Syrain hamster in the middle of the 201

century. Since this time the

number of researches on the HG has increased.

Although, the major interest was focused on mammals, the study of the HG in non mammalian tetrapods was resumed recently. One of the main characteristics of this gland is the extreme variety not only of its morphology at the ultrastructural level but also its functions and secretory products. The extreme variation at the ultrastructural levels is not only present among classes but also among orders, families, genera and species, that the morphology of the gland in any unknown species can not be safely inferred existing reports, and broad generalizations relating gland structure to taxonomic status, ecology or function cannot be made. The extreme variation in the secretory products and functions m addition to structure is related to different adaptations of the species considered. The Synthesis of porphyrins and melatonin by the rodent HG, is not shared by other mammalian and non mammalian species. The lipid component of the harderian secretion is more diffused among different species although it seems to perform different functions in the same or different species.