Tongues were removed from fetuses of mice on the 15th day of gestation (E15), from newborns (P0), and from juveniles on the 7th day (p7) and on the 21st day (P21) after birth for examination by light microscopy and transmission electron microscopy. In the fetuses at E15, no rudiments of filiform papillae were visible on the dorsal surface of the tongue. No evidence of keratinization was recognized throughout the entire dorsal lingual epithelium. At P0, rudiments of filiform papillae were compactly distributed over the dorsal surface, as are the filiform papillae in the adult, but their tips were rounder than those of the filiform papillae in the adult. Cell columns in the epithelium, with different degrees of keratinization of the type observed in the matured adult were indistinct. However, a keratinized layer was clearly visible on the tip of each filiform papilla. In juveniles at P7, the filiform papillae on the anterior part of the tongue were long and slender, and the anterior and posterior cell columns of the filiform papillae were identical to those in the adult. These results indicate that, in mice, the morphogenesis of filiform papillae advances in parallel with keratinization of the lingual epithelium from the stage just before birth to a stage a few weeks after birth.

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