The myology of the Amazonian Manatee, Trichechus inunguis (Natterer) (Mammalia: Sirenia)

ABSTRACT: The muscles of the Amazonian manatee are described and compared with those of other manatees and the dugong. Maps of muscle attachments and data on weights of muscles are included. The manatee species differ in the forms of the mm. rectus capitis lateralis and biceps brachii. The mechanisms of protrusion of upper-lip bristles and opening of the nostrils are described. The jaw apparatus is uniquely specialized, with a very large temporalis muscle constituting more than half the adductor muscle mass, and development of a joint between the pterygoid process and the mandible which probably braces the mandible during transverse chewing. The center of mandibular rotation in transverse chewing probably lies posteromedial to the pterygoid process on the active side: the contralateral temporalis is dominant in transverse chewing. Trichechus inunguis is more specialized for surface-feeding and for swimming than T. manotus.