Data derived from studies of comparative anatomy,
development, neuroanatomy, behaviour and the reconstruction of fossils
are combined to evaluate the evolution of the oral-pharyngeal region in
mammals. An important event in the evolution of the mammalian feeding
apparatus was the development of a novel neuromuscular apparatus, consisting
of a large series of striated muscles. The most important of these
muscles are the pharyngeal elevators and constrictors, which appear to
be without homologues in other amniotes. In addition to considerable
peripheral neural and muscular modifications, the motor nuclei of the brain
stem in mammals exhibit significant differences from other amniotes.
The morphological features characteristic of mammals are reflected in behavioural
differences, most significantly during swallowing and suckling. The
neuromuscular changes in the mammalian oral-pharyngeal apparatus are at
least as extensive as those involving the masticatory system, and have
importance far beyond the separation of the airway and foodway, the foci
of most previous studies. The hypothesis of neuromuscular conservatism
in the evolution of the mammalian feeding mechanism is considered and it
is concluded that few data exist to support this hypothesis.