Fibre composition of the masticatory muscles of Pteropus giganteus (Megachiroptera).

Routine histochemistry was used to study fibre type composition of the masticatory muscles of the frugivorous flying fox, Pteropus giganteus (BRUNNICH, 1782). Frozen sections were stained for alkaline- and acid-stable ATPase, NADH-tetrazolium reductase and alpha-glycerophosphate dehydrogenase, and fibres were subsequently identified as slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG) and fast-twitch glycolytic (FG). Based upon relative proportions of fibre types, muscles and their subdivisions can be classified into three groups: group 1 muscles (superficial and medial temporales), containing less than 10 \% of SO fibres, group 2 muscles (superficial and deep masseter, zygomaticomandibularis, deep temporalis, medial pterygoid), containing 20-30 \% of SO fibres, and group 3 muscles (anterior and posterior digastrics), containing 30-50 \% of SO fibres. Moreover, in group 3 muscles less than 5 \% of the fast twitch fibres are fatigue resistant (FOG), whereas in both group 1 and 2 muscles, about 20-30 \% of the fast-twitch fibres are FOG. The histochemical profile of the masticatory muscles is correlated directly with their contraction characteristics and indirectly with their EMG patterns.