TIMING IN THE MOVEMENT OF JAWS, TONGUE, AND HYOID DURING FEEDING IN THE HYRAX, PROCAVIA-SYRIACUS

The anatomical structures used during mammalian feeding are morphologically linked by their connecting musculature, suggesting a predictable timing relationship among their movements. Cine-x-ray (100 frames per second) was used to record feeding behavior in four adult hyraxes (Procavia syriacus), herbivores. Movement of jaws, tongue, and hyoid bone was cyclic, and prior to the first swallow cycle, cycle duration was constant through time for all structures. Minimum gape, beginning of forward movement of the tongue and hyoid and beginning of intrinsic tongue expansion occurred simultaneously over a large number of cycles. However, maximum gape, maximum protrusion of hyoid, and maximum forward position of the tongue happened at statistically different points in time. After the first swallow, cycle duration increased. Most of the variation in cycle duration can be explained by variation in the opening or forward phase of movement; the closing and return phases are constant in duration. These results are a quantitative description of the coordination that exists during different feeding behaviors (ingestion, intraoral transport, mastication, and swallowing) in normal, freely functioning hyraxes. The patterns of phase duration differ from some results obtained by using anesthetized animals.