Morphological observations on the papillae of the opossum tongue.

The dorsum of the opossum tongue shows filiform, fungiform, conical and three vallate papillae. An additional type, the compound filiform papilla, is characteristic of most marsupials, including the opossum. These are unique structures in which the epithelium forms fringe-like, keratinized projections around the apical borders of the papillae. The covering epithelium is an extensively keratinized, stratified squamous type with a well-developed stratum granulosum containing numerous keratohyalin granules. Large, heavily cornified conical papillae occur in a patch near the anterior end of the tongue and the apex of each papilla is directed posteriorly. Taste buds are associated with only the three vallate papillae which form a triangle near the base of the tongue. They are not present on the fungiform papillae or in the posterolateral mucosal folds which appear to replace the foliate papillae of other species.