[Functional structure of the human vocal cord]

19 laryngeal specimens (11 male, 8 female) were cut in horizontal serial sections, parallel to the free edge of the vocal cord. After staining, the structures of the glottis were measured microscopically and statistical analysis of the sex-related differences performed. The results show that the glottis can be divided not only into the well-known anterior and posterior glottis, but into five histological and functional distinctive portions. Within the anterior glottis, these parts are the freely vibrating midportion of the vocal cord, which is connected to the stiff laryngeal frame via an anterior and posterior transition zone. Within the posterior glottis there are two parts: the vocal process of the arytenoid cartilage (which is, according to Hirano, also the cartilage portion of the vocal cord) and the lateral wall of the posterior glottis. Statistical analysis of the data revealed significant sex differences, not only in the absolute measures but also on comparing the relative dimensions in respect of the total glottic length. The posterior glottis accounts for 37% of the total glottic length in men and for 42% in women and is therefore longer than generally accepted. We found statistically significant sex-related differences in the length of the posterior glottis, which is absolutely longer in men but relatively longer in women. The reason for this is the difference in the length of the midportion of the vocal cord. This zone is twice as long in men (8.5 mm) than in women (4.6 mm) and accounts for 37% of the total glottic length in men compared to 29% in women. As this portion is the most vibrating part of the vocal cord this could be an explanation for the unsolved phenomenon why the fundamental frequencies are 1:2 between men and women while all dimensions of the larynx are 1.5:1. The vibrating midportion of the vocal cord is connected to the stiff laryngeal framework by highly differentiated transition zones: the nodulus elasticus anterior and posterior. The lamina propria of the midportion shows a three-layered structure, orientated parallel to the free edge of the vocal cord. In the transition zones the deep layer of the lamina propria consists of interwoven bundles of collagen and elastic fibres, thus having the function of a "cushion ball" (Hirano). A functionally important portion is the vocal process of the arytenoid cartilage. The complex movements of the vocal process during abduction and adduction of the vocal cords produce a severe mechanical strain on the mucous membrane covering this part of the glottis.