The structure and function of muskox preorbital glands

Abstract

The preorbital gland of the muskox is a relatively large pear-shaped structure lying rostral to the eye between the skin and the lacrimal bone. It surrounds a narrow tubular invagination of the skin, which conveys the largely aqueous secretion to the surface of the face. This tube, which enters the gland at its rostrolateral extremity and runs caudodorsally, is partially filled with stiff hairs that arise from follicles in its wall. Most of the gland consists of tightly packed apocrine sweat glands, but large sebaceous glands are associated with the hair follicles of the central tube. The myoepithelium of the sweat glands is highly developed but the facial muscles overlying the gland are very thin and probably do not contribute significantly to the expulsion of secretion. Secretion is mechanically expressed when the animal rubs the area of the gland on something firm such as its own foreleg (gland rubbing) or a prominent object in the environment (rubbing). The gland is functional in both sexes throughout the year but is much larger in males. In the wild, scent marking and gland rubbing occur during aggressive encounters between individuals within a herd, between herds, and between muskoxen and other species. Gland rubbing in females and subadults is usually restricted to interspecific encounters but in males it occurs in most intense agonistic situations. Wild calves performed the self-marking behaviour as early as 1 week of age when play fighting. Captive muskoxen did not rub their preorbital gland on the foreleg but commonly rubbed it on objects. The authors believe that the principal function of the preorbital gland is to provide an olfactory component of the threat behaviour pattern.