Preorbital gland
The preorbital gland is a paired exocrine gland found in many species of artiodactyls, which is homologous to the lacrimal gland found in humans. These glands are trenchlike slits of dark blue to black, nearly bare skin extending from the medial canthus of each eye. They are lined by a combination of sebaceous and sudoriferous glands, and they produce secretions which contain pheromones and other semiochemical compounds. Ungulates frequently deposit these secretions on twigs and grass as a means of communication with other animals.The preorbital gland serves different roles in different species. Pheromone-containing secretions from the preorbital gland may serve to establish an animal's dominance (especially in preparation for breeding), mark its territory, or simply to produce a pleasurable sensation to the animal.