Three-dimensional fine structure of the lingual papillae and their connective tissue cores in the human tongue.

The three-dimensional structure of the four types of lingual papillae and their connective tissue cores (CTCs) in the human tongue was studied by scanning electron microscopy after removal of the epithelial cell layer, and was compared to those of other mammalian species. Filiform papillae are densely distributed on the dorsal surface of the anterior two-thirds of the tongue. Each filiform papilla has numerous slender protrusions on the top. After removal of the epithelium, the CTC of the filiform papilla has a columnar primary core with 10-30 rod-shaped small secondary cores surrounding an upper central depression. A few long spine-like protrusions are frequently found in the center of this upper depression. The number, thickness and length of each secondary protrusion of the filiform CTC show some variations at the region distributed on the tongue. Fungiform papillae with spherical heads are scattered among these filiform papillae and are numerous at the anterior margin of the tongue. The CTC of the fungiform papilla shows a coralliform structure with numerous small rod-shaped protrusions on the lateral surface, and its branched top has flat areas with a few small round depressions harboring taste buds. It must be emphasized that human fungiform papilla has some taste buds not only in the young, but also in the adult age. Several to 12 vallate papillae are distributed in front of the terminal groove and had the CTC of pinecone-like structure with numerous small thorns (secondary connective tissue cores). Foliate papillae consist of 10-15 parallel folds at the posterior margin of the tongue. The CTC of the foliate papillae appears as ridges and grooves. Small protrusions are scattered on the surface of the ridges. The underside view of the exfoliated epithelium of the vallate as well as the foliate papillae revealed numerous taste buds arranged in single file in the lateral epithelium. The dorsal surface of the root of the tongue has evenly distributed short rod-shaped protrusions of the connective tissue.