Fine structure of the dorsal epithelium of the mongoose tongue

The epithelium of the lingual dorsum of the mongoose, Herpestes edwardsi, was composed of two main areas: the interpapillary area, characterised by the absence of keratinisation; and the papillary area, characterised by hard keratinisation. The number of tonofibrils in the cytoplasm gradually increased, and the volume of the individual cells also increased, from the germinal layer to the intermediate layer of the interpapillary epithelium. No keratohyalin granules were recognised in these cells. In the cells of the surface layer of the interpapillary epithelium, most of the cytoplasm was filled with tonofilaments. The germinal layer of the papillary epithelium was almost identical to that of the interpapillary epithelium. In the intermediate layer, three different types of keratohyalin granule were apparent. The first type consisted of loosely aggregated ribosomes and had moderate electron density. The second type consisted of electron-dense granules derived from granules of the first type. The third type consisted of conjugated structures made up of tonofibrils, which were embedded in electron-dense material. Free ribosomes gradually disappeared as the keratinised layer was approached and most of the cytoplasm of cells in this layer was filled with keratin fibres.