Prenatal development and innervation of the circumvallate papilla in the mouse.

The embryonic development of the circumvallate papilla in the mouse is described. Serial sections of Day 11 to Day 18 mouse embryos were stained by Linder's silver method and examined to determine the temporal events in relation to circumvallate papilla formation. This was complemented by scanning electron micrographs. On Day 13, the earliest sign of a single median circumvallate papilla formation was visible as an epithelial invagination which had bilateral nerve innervation. Scanning electron micrographs of this stage showed a median flattened area demarcated at its periphery by cells invaginating from the surface. On Day 14, the epithelial invagination appeared like an inverted cup with a dense nerve plexus within its core. By the afternoon of Day 14 a furrow had formed by a split in the epithelium. During that period the surface morphology changed from a flattened area to a central dome-shaped structure. As development progressed the furrow became accentuated by the elevation of its lateral walls. Nerve fibres penetrated the epithelium, but taste bud differentiation was not easily observable. The dense innervation of the circumvallate papilla was established from the start of its formation. The role of these nerves as an inductive factor or as providing a trophic effect on the formation of the circumvallate papilla remains to be investigated.