Comparative histochemistry of human and sheep laryngeal muscles.

Four laryngeal muscles of human male, human female and sheep female cadavers were evaluated by histological, histochemical and quantitative techniques. The muscle fibre sizes showed significant differences between human male, female and sheep. Fibre diameters of male human laryngeal muscles were 2 to 4 microns larger than in female human and 11 to 13 microns larger than in sheep muscles. In the group of human laryngeal muscles, the posterior cricoarytenoid muscle contained the highest percentage (65%) of type I fibres. In sheep, the homologous muscle consists only of 45% type I fibres. On the other hand, in sheep the cricothyroid muscle showed significantly more type I fibres (58%) than the human counterpart (43%). In both species the vocal muscles had a rather low content of type I fibres (26 to 37%).