Correlated TEM, SEM, and histological observations of filiform papillae of the cow tongue.

The ultrastructural and histological characteristics of the filiform papillae of the cow tongue are described. These large, conical papillae display a fully keratinized external projection, which demonstrates a dominant hard keratin core partially ensheathed by soft keratin. This biostructure differentiates from a dominant posterior cell line, leading to the hard keratin core, and a thinner anterior cell line which, with contributions from an interpapillary cell line, appears responsible for an attenuating sheath of soft keratin around the hard keratin core. The hard keratin cell line differentiates from cells devoid of keratohyalin granules (KHG), which are rich in thick bundles of tonofilaments. The soft keratin cell line differentiates from cells containing both eosinophil and basophil KHG and dispersed tonofilaments. The bovine filiform papilla also appears similar in biostructure to the mammalian hair shaft and the 'filiform hairs' of the rat penis.