THE MUSCULAR HYDROSTAT OF THE FLORIDA MANATEE (TRICHECHUS-MANATUS LATIROSTRIS) - A FUNCTIONAL MORPHOLOGICAL MODEL OF PERIORAL BRISTLE USE

Facial musculature was examined in the Florida manatee, Trichechus man atus latirostris, in order to develop a functional model of perioral b ristle use. Muscles identified include the M. levator nasolabialis, M. buccinatorius, M. maxillonasolabialis M. centralis nias,, M. laterali s nasi, M. sphincter colli profundus pars oris, M. orbicularis oris, M . mandibularis, and M. mentalis. A new muscle, M. centralis nasi, has been named and is an integral part of perioral bristle movement. The s nout of the Florida manatee is capable of performing complex movements . The prehensile ability of Florida manatees can be explained in the c ontext of a muscular hydrostat as defined by Kier and Smith (1985). Ev ersion of certain bristles in the upper lip occurs by shortening longi tudinal, transverse, and semicircular muscles in combination with volu me displacement due to compensatory changes in the shape of the snout. Midline sweeping of these bristles is accomplished by the contraction of M. centralis nasi. Eversion of bristles on the lower jaw is a resu lt of shortening of hi. mentalis. Contraction of M. orbicularis oris p ushes vegetation into the oral cavity. All observed movement patterns and uses of perioral bristles can be explained by variation of these s equences within the context of muscular hydrostat function.