Particular structure of the anterior third of the human true vocal cord

The histological aspects of the true vocal cord mucosa change in the anterior third compared with the posterior two thirds. The anterior third is characterized by an epithelium where the ridges, marked in the posterior two thirds, are very slight or even absent. The underlying basement membrane, which is thin in the posterior two thirds, here appears particularly thick. At the ultrastructural level in this area, beneath a normally thickened basal lamina, a thick layer of finely granulated electron-dense material, interspersed with thin and randomly scattered collagen fibrils and proteoglycan filaments, is detectable. Beneath this thickened basement membrane, a layer of small undulated collagen fibril bundles with very numerous interspersed oxytalan fibres is found. The collagen fibrils, small in diameter (30-40 nm), seem to continue with the collagen fibrils of the basement membrane. In this layer numerous blood vessels with a very thick, delaminated basement membrane are also observed. The underlying area is characterized by the vocal cord ligament, composed by large compact collagen fibril bundles with interspersed elastic fibres. The particular features of the thick basement membrane, the thick-walled and delaminated vessels and the modular distribution of the elastic system together may well form the basic structure enabling the functional integration of the vocal ligament into the overlying mucosa and the underlying vocal muscle.