No mammal survives to reproductive age without first suckling and then adapting to a diet of semi-solid or solid foods during weaning. That process is associated with significant ontogenetic change in the anatomy of the orofacial complex, and in the mechanisms by which food is moved through the mouth to the oropharynx and into the digestive tract. Much attention has been paid to the morphology of cercopithecoid teeth and jaws (Warwick James, 1960; Swindler, 1976; Kay, 1978; Lucas and Teaford, 1994) and there is even more information on chewing in humans. However, the anatomy and role of the soft tissues, especially the tongue-hyoid complex, have largely been ignored. It is now clear that the feeding process depends as much on the soft tissues of the mouth and pharynx as on the teeth and jaws.
The events involved in moving food from the external environment into the mouth and through the pharynx into the gastrointestinal (GI) tract constitute the feeding sequence (Fig. 8.1). This is conventionally described (based on non-primate studies) as having three sequential elements, usually occurring seriatim: ingestion; mastication (chewing); and deglutition (swallowing). In all mammals so far studied, these processes depend on patterned behavior of the hard and soft tissue components of the system. Two fundamental mechanisms are involved: food transport, which is a tongue dependent function; and food breakdown, which is largely achieved by the relative movement of upper and lower teeth as a function of jaw movement (Fig. 8.1).