Abstract
The myofibrous organization of the laryngeal muscles of the dog was investigated and compared with those of macaque and man to elucidate relations between vocalization and laryngeal muscle morphology. In macaque and man, the innervation ratio of each laryngeal muscle was also analyzed. Materials and method : Materials included a male dog, a female dog, a male Japanese macaque and 4 male humans (ages in forties and fifties) . The dog laryngeal muscle fibers were stained with Sudan Black B and classified into three types. The laryngeal muscle fibers of the men and the macaque were stained with hametoxyline eosin and the nerve fibers were stained with toluidine blue. Results : 1. The laryngeal muscles of the dog did not include the musculus epiglotticus or arytenoideus obliquus which were observed in man and chimpanzee, but they did include the musculus ventricularis. 2. The cross sectional area and the total numbers of muscle fibers of the musculus cricothyroideus were the largest of the dog laryngeal muscles. Those of the musculus thyroarytenoideus including the musculus vocalis were the second largest, and those of the musculus ventricularis were smallest. Generally, all values were larger in male than in female. 3. The frequency of the white muscle fiber of each laryngeal muscle of the dog was highest and was followed by the intermediate muscle fiber. The female white muscle fiber frequency was higher than that of the male. Thickness of the muscle fibers decreased in the order of white, intermediate and red muscle fiber. The white muscle fibers of the musculi cricoarytenoideus dorsalis, cricothyroideus and arytenoideus transversus were larger. Although the order of the muscle fiber types in the female dog was same as that in the male, differences between the muscle fiber sizes of the intermediate and red muscle fiber were less than those of the male. The male muscle fibers tended to be larger. 4. Comparison of the laryngeal muscles of the dog with those of man, chimpanzee, Japanese macaque and galago revealed that the muscles of the chimpanzee were most similar to those of the dogs. Most of the laryngeal muscles of the dog were larger, and were more frequently white muscle fiber than those of men. 5. The ratios of muscle fibers per myelinated nerve fiber in man and macaque were compared. The ratios for all of the laryngeal muscles of man were smaller than those of macaques. Thus, a more dense ratio of innervation in man was concluded. The difference in this ratio was remarkable in the musculi thyroarytenoideus and arytenoideus transversus. Though the numbers of laryngeal muscles of man and macaque were similar, those of dog and man were much different, because of the remarkable differences in the numbers of each muscle.
