Food transport through the anterior oral cavity in macaques

Intraoral transport, the movement of food or liquid through the oral cavity and oropharynx, is a major component of feeding behavior. Stage I transport, transport through the oral cavity prior to mastication, has been described for several mammals (Franks et al.: Arch. Oral Biol. 30:539, 1985; Hiiemae and Crompton: Hildebrand et al. (eds.): Functional Vertebrate Morphology, Cambridge, MA, Belknap Press, 1985). Previous work (Franks et al.: Am. J. Phys. Anthropol. 65:275, 1984) indicated that this was not a significant behavior in macaques in a laboratory setting, because food was ingested directly to the region of the cheek teeth. Although relatively infrequent in a captive situation, stage I transport does occur in long-tailed macaques through a mechanism similar to other mammals, but also subject to unique aspects of primate anatomy. Transport takes several cycles during which the food moves back and forth in an anterior/posterior direction, due to tongue movements. Because anthropoid primates lack the pronounced rugae that in other mammals prevent the anterior displacement of a bolus, stage I transport uses the rounded arch of the upper, anterior dentition to hold the food during the forward movement of the tongue. During the final cycle of transport, a pronounced twisting of the tongue, along a midline anteroposterior axis helps funnel the food item toward the postcanine teeth for subsequent mastication. This twisting, which was described in humans by Abd-El-Malek (J. Anat. 100:215, 1955) but not within the context of jaw movement, occurs prior to the closing phase of the jaw cycle.