Tongues were removed from rat fetuses on d 16 of gestation (E16) and from newborn (P0) and juvenile
rats on d 7 (P7) and d 21 (P21) postnatally for examination by light and transmission electron microscopy.
In the fetuses at E16, no rudiments of filiform papillae were visible on the dorsal surface of the tongue. No
evidence of keratinisation could be recognised over the entire dorsal lingual epithelium. At P0, rudiments of
filiform papillae showed a similar distribution to that seen in the adult, but had a more rounded appearance.
The columnar structure of cells in the epithelium, with the different degrees of keratinisation as observed in
the mature adult, was indistinct, but a keratinised layer was clearly located at 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 and the interpapillary cell columns were
clearly distinguishable. In juveniles at P21, the structure of filiform papillae was identical to that in the
adult. These results indicate that, in rats, the morphogenesis of filiform papillae advances in parallel with
keratinisation of the lingual epithelium from just before birth to a few weeks after birth.