Abstract
Histochemical muscle fiber composition was studied in hyoid muscles from 4 rats (2 males, 2 females) . Muscle fibers were classified as white, intermediate and red by lactate dehydrogenase (LDH) activity. The following results were obtained: 1) Cross-sectional area of sternohyoid muscle and the anterior belly of digastric muscle were larger than those of other hyoid muscles, and were remarkably smaller than those of lower limb and trunk muscles. No sex differences were observed. 2) The number of muscle fibers per sq. mm was smallest in omohyoid muscle. Suprahyoid and thyrohyoid muscles were larger than lower limb and trunk muscles. 3) The anterior belly of digastric muscle had the most total muscle fiber, and this was equal to that of sternomastoid muscle which had the least in the lower limb and trunk. 4) The percentages of white muscle fibers were greatest in the posterior belly of digastric muscle, sternohyoid muscle and omohyoid muscle, and the red muscle fiber was most predominant in mylohyoid muscle. Intermediate fibers were most predominant in other muscles. 5) Fiber size of white muscle fibers was largest, and that of red fibers was smallest in each hyoid muscle, and no sex differences were observed. Muscle fiber size was remarkable smaller than that of the lower limb and trunk muscles. Muscle fiber sizes of each types were larger in sternohyoid and omohyoid muscle than in other hyoid muscles. The fiber size in transverse-mandibula muscle was smallest.
