ON THE FUNCTIONAL STRUCTURE OF THE HUMAN VOCAL CORD

19 laryngeal specimens (11 male, 8 female) were cut in horizontal seri al sections, parallel to the free edge of the vocal cord. After staini ng, the structures of the glottis were measured microscopically and st atistical analysis of the sex-related differences performed. The resul ts show that the glottis can be divided not only into the well-known a nterior and posterior glottis, but into five histological and function al 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 proc ess of the arytenoid cartilage (which is, according to Hirano, also th e cartilage portion of the vocal cord) and the lateral wall of the pos terior glottis. Statistical analysis of the data revealed significant sex differences, not only in the absolute measures but also on compari ng 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 len gth of the posterior glottis, which is absolutely longer in men but re latively 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 lon g in men (8.5 mm) than in women (4.6 mm) and accounts for 37% of the t otal glottic length in men compared to 29% in women. As this portion i s the most vibrating part of the vocal cord this could be an explantio n 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. Th e vibrating midportion of the vocal cord is connected to the stiff lar yngeal framework by highly differenciated transition zones: the nodulu s elasticus anterior and posterior. The lamina propria of the midporti on shows a three-layered structure, orientated parallel to the free ed ge of the vocal cord. In the transition zones the deep layer of the la mina propria consists of interwoven bundles of collagen and elastic fi bres, thus having the function of a ''cushion ball'' (Hirano). A funct ionally important portion is the vocal process of the arytenoid cartil age. The complex movements of the vocal process during abduction and a dduction of the vocal cords produce a severe mechanical strain on the mucous membrane covering this part of the glottis.