抄録
The histochemical organization observed in cross sections of rat masseter muscle was investigated by staining for succinic dehydrogenase. Most primary fasciculi were composed of three muscle fiber types: type A, B and C classified by Stein and Padykula (29). Significant differences in the percentage of type B plus type C fibers (Pbc) and the percentage of type C fibers (Pc) were found in different regions (origin, belly, and insertion), and in different parts (the deepest masseter, anterior deep and posterior deep masseter, and superficial masseter). Moreover, marked differences were found in the percentage distributions of Pbc and Pc of different primary fasciculi in each part of the masseter. In general, the average Pbc and Pc values were highest in the deepest masseter, intermediate in the superficial masseter, and lowest in the deep masseter in the origin and belly portions. In aging rats the three kinds of muscle fibers were easier to distinguish and differences in the average Pbc and Pc values in different muscle parts were greater. Moreover, primary fasciculi with high Pbc and Pc values, or those with low Pbc and Pc values were more numerous than in young adult rats.
