ELECTROMYOGRAPHY AND MECHANICS OF MASTICATION IN THE SPRINGHARE, PEDETES CAPENSIS (RODENTIA, PEDETIDAE)

In springhares, Pedetes capensis (FORSTER, 1778) ingestion, transport and mastication of food are cyclic events. During these cycles, the mo vement of the lower jaw shows no lateral component and the activity of all muscles is bilaterally symmetrical. The temporal muscles reach a peak activity during the fast-closing stage. During the reduction stag es, peak activities are subsequently reached in the maxillomandibular muscles, the medial pterygoids, the masseters, the zygomaticomandibula r muscles, the posterior masseters, and the lateral pterygoids in orde r. During fast opening, only the digastrics fire bilaterally. Magnitud e and duration show some variation for the different types of food off ered. The maxillomandibular muscle reaches its maximum activity whenev er the animals feed on groundnut. Food that does not require biting (i .e. rolled oats), produces very low muscle activity. The Rodentia incl ude groups with a similar gross muscular morphology but considerable d ifferences in their masticatory patterns, whereas members of different major groups show similar masticatory patterns. Although the masticat ory patterns shown by Rattus and Pedetes are similar, the forces actin g on their lower jaws differ. In Pedetes the masseter-complex is more important than in Rattus as the bite force at the incisors is 68% of t he estimated muscle resultant.