The facial musculature of the Suoidea

The facial musculature and rhinarial anatomy of a tayassuid, Dicotyles, and four suids, Sus, Hylochoerus, Phacochoerus and Babirussa, are described. Differences found include the lack of m. zygomaticus in Hylochoerus and Phacochoerus and several modifications of the rostral muscles, mm. levator rostri, dilator naris, and depressor rostri. These differences are related to behavioral characteristics of the animals, particularly the occurrence of toothbaring and rhinarial mobility. The missing m. zygomaticus and relatively small mouth of Hylochoerus and Phacochoerus are probably associated with behavioral patterns which do not necessitate a large gape. In these genera the canines are exposed even when the mouth is closed. The development of the rostral musculature is correlated with movements of the rhinarium. Similarly, the distribution of terminal tendons depends on the shape of the nostril. In Hylochoerus and Phacochoerus, mobility of the rhinarium, especially the dorsal part, is less than in other suoids because of the firmer attachment of the rostral bone to the skull and the weaker development of the rostral muscles.