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FACIAL EXPRESSION AND OTHER FACIAL MUSCLES
     Lower vertebrates have very few muscles of the face and very little if any facial expression is possible.  This musculature increases in mammals in general and especially in primates. At least some of the muscular and neural mechanisms of facial expression in humans seems to be homologous to the facial expression in other primates (Parr, 2005).
face

FROG

FROG

TURTLE

TURTLE

OPOSSUM

FACIAL MUSCLES

RISORIUS

CAT

ORBICULARIS ORIS

PIG

PIG FACE

HUMAN MODEL

MODEL

    Mammals possess muscles which move the external ear.  Humans still possess these muscles, although most people cannot move their ears and even those that can are unable to move their ears to better hear sounds from a certain direction.
OPOSSUMEAR MUSCLES

CAT

EAR MUSCLES

MONKEY

MUSCLES

HUMAN MODEL

EAR MUSCLES

   With the loss of the gill arches in amphibians, muscles from the gill arches (hyobranchial muscles) become incorporated into the tongue and attached to the remnants of pharyngeal arch cartilages which form the hyoid.  The hypobranchial musculature produces glossus and hyoid groups of muscles (Kardong, p. 378; Romer, p. 288-9)  Once the operculum was lost, the hyoid arch musculature expanded into the neck (Romer, p. 309). The tendon of the nictitating membrane to the pyramidalis muscle and the pyramidalis muscle are absent in mammals but present in non-mammalian amniotes (Gauthier, 1988).