Scanning electron microscope study of tongue development in the CD-1 mouse fetus.

The objective of this study was to examine three dimensionally the embryonic and fetal stages of tongue development with scanning electron microscopy. Time-bred CD-1 mice were sacrificed at quarter-day intervals on days 10-13, and at half-day intervals on days 13.5-16.5 of gestation. Fetal tongues were dissected and fixed in s-collidine buffered 4% glutaraldehyde at pH7.4, and subsequently processed for SEM viewing. Tongue development was initiated on the 11th day by the appearance of the tuberculum impar and the two lateral lingual swellings on arch I. This was followed by the elevation of the hypobranchial eminence, which unites arches III and IV in the ventral midline, and overgrows arch II anteriorly. During the 12th day, remodeling occurred in areas of arches II and III, forming the root of the tongue. A cone-shaped midline swelling, the epiglottis, appeared in the ventral midline of arches III and IV. By the 13th day, the general proportions of the tongue, occupied by the body, root, and epiglottis, were established. The single circumvallate papilla and fungiform papillae were initiated during the early part of the 13th day, followed on the 15th day by differentiation of filiform and foliate papillae and raised nodules of lingual tonsilar tissue. The SEM study documented the temporal and morphological sequence of events during mouse tongue development. The tuberculum impar persisted to the late fetal stages and may therefore contribute largely to the dorsum of the tongue anterior to the circumvallate papilla.