HILLENIUS, W.J.*; REHOREK, S.J.; DAWSON, S; College of Charleston, SC; University of Slippery Rock, PA; National Zoo, Washington, DC: The Preorbital Apparatus of Muntjacs 2: Facial Musculature

A preorbital fossa, a depression in the lateral surface of the skull, anterior to the eye, occurs in several ungulate mammals, but is especially well-developed in bovid and cervid artiodactyls. Although the fossa contains a single, well-developed and encapsulated gland in several antelopes, in other bovids and deer it is lined by a sac of relatively unmodified skin, which contains only a few more glandular elements than the surrounding skin. These structures appear to play a role in chemical signaling in most, if not all, of these animals. Muntjacs (Cervidae: Muntiacinae) are diminutive, rather primitive deer, that are characterized not only by a proportionately large preorbital fossa, but also by their ability to open and even evert the sac, exposing its contents. In a previous study we noted that the preorbital sac of Muntiacus reevesi is subdivided into two pockets, and exhibits considerable sexual dimorphism in glandular development. Here we describe the facial musculature that underlies the preorbital sac, and compare it to that of Cervus and Odocoileus. The sac appears to be an anterior extension of the medial canthus of the eye, and lies ventral to the raphe by which the various preorbital muscles attach to the lacrimal bone. In comparison to the other deer, however, the sac of Muntiacus is deeper and proportionately longer, and the underlying musculature, especially m. malaris, is more specialized. Eversion of the sac is achieved by combined action of the frontal, nasolabial, malar and orbicular eye muscles.