Abstract
Histochemical studies were made of the masticatory (temporal, masseter and digastric) muscles of the laboratory mouse, Mus musculus, and laboratory rat, Rattus norvegicus, which are omnivorous, the golden hamster, Mesocricetus auratus, which is omnivorous but with a tendency to eat much vegetable matter, and the Japanese field vole, Microtus montebelli, which is herbivorous. It was found that the masticatory muscles were composed almost entirely of fast-twitch fibers. Interspecific differences were found in the oxidative enzyme activity of the masseter muscle in relation to rodent dietary habits. The masseter muscles of the mouse and rat consisted of fast-twitch oxidative glycolytic and fast-twitch glycolytic fibers, thus they appear to have the capacity for powerful, or sudden, and enduring contractions. The masseter muscles of the hamsters were composed only of fast-twitch intermediate fibers, thus giving them the capacity for moderately enduring contractions, whereas the vole masseter muscles consisted only of fast-twitch oxidative fibers, and consequently they appear to have the capacity for particularly enduring contractions.
