Composition of myofiber types in the vocalis muscles involved in rapid closure of the glottis in Japanese macaques.

Myofiber types of the medial thyroarytenoid (vocalis) muscle, lateral thyroarytenoid muscle, and cricothyroid muscle of the Japanese macaque were examined with enzyme-histochemical methods. For comparison, the semitendinosus muscle of the Japanese macaque and the thyroarytenoid (vocalis) muscle of cattle, sheep, and pig were examined with the same methods. The vocalis muscle of the Japanese macaque was composed exclusively of fast-twitch/oxidative/glycolytic (FOG) myofibers; it differed from the lateral thyroarytenoid, cricothyroid, and semitendinosus muscles of the Japanese macaque and from the vocalis muscles of the other animals, which consisted of slow-twitch/oxidative, FOG-, and fast-twitch/glycolytic myofibers or type IIC myofibers. The histochemical properties of the vocalis muscle of the Japanese macaque show that the vocalis muscle has a capacity to close the glottis rapidly and completely.