aberrant formation or incomplete differentiation of the sebaceous gland located behind the eyeball that excretes fluid that facilitates movement of the nictitating membrane; in rodents, the Harderian gland originates from the nasal part of the conjunctival epithelium at E16 and forms a branched structure behind the eyeball; in contrast to the acinar morphology of the lacrimal gland, the Harderian gland has a tubulo-alveolar organization and is composed exclusively of one type of secretory cell; in primates, the HG is either absent or vestigial