 Circumvallate papillae are the large, dome-shaped structures that reside in the mucosa just anterior to the sulcus terminalis (see Fig. 16.3). The human tongue has 8 to 12 of these papillae. Each papilla is surrounded by a moatlike invagination lined with stratified squamous epithelium that contains numerous taste buds (Fig. 16.4d). Ducts of lingual salivary (von Ebner’s) glands empty their
FIGURE 16.3 • Human tongue. Circumvallate papillae are positioned in a V configuration, separating the anterior two thirds of the tongue from the posterior third. Fungiform and filiform papillae are on the anterior portion of the dorsal tongue surface. The uneven contour of the posterior tongue surface is attributable to the lingual tonsils. The palatine tonsil is at the junction between the oral cavity and the pharynx.
serous secretion into the base of the moats. This secretion presumably flushes material from the moat to enable the taste buds to respond rapidly to changing stimuli.
 Foliate papillae consist of parallel low ridges separated by deep mucosal clefts (see Fig. 16.4c and Plate 50, page 561), which are aligned at right angles to the long axis of the tongue. They occur on the lateral edge of the tongue. In aged individuals, the foliate papillae may not be recognized; in younger individuals, they are easily found on the posterior lateral surface of the tongue and contain many taste buds in the epithelium of the facing walls of neighboring papillae (Fig. 16.3e). Small serous glands empty into the clefts. In some animals, such as the rabbit, foliate papillae constitute the principal site of aggregation of taste buds.
The dorsal surface of the base of the tongue exhibits smooth bulges that reflect the presence of the lingual tonsil in the lamina propria (see Fig. 16.3).
FIGURE 16.4 • Lingual papillae. a. Structurally, the filiform papillae are posteriorly bent conical projections of the epithelium. These papillae do not possess taste buds and are composed of stratified squamous keratinized epithelium. 45. b. Fungiform papillae are slightly rounded, elevated structures situated among the filiform papillae. A highly vascularized connective tissue core forms the center of the fungiform papilla and projects into the base of the surface epithelium. Because of the deep penetration of connective tissue into the epithelium (arrows), combined with a very thin keratinized surface, the fungiform papillae appear as small red dots when the dorsal surface of the tongue is examined by gross inspection. 45. c. In a section, foliate papillae can be distinguished from fungiform papillae because they appear in rows separated by deep clefts (arrows). The foliate papillae are covered by stratified squamous nonkeratinized epithelium containing numerous taste buds on their lateral surfaces. The free surface epithelium of each papilla is thick and has a number of secondary connective tissue papillae projecting into its undersurface. The connective tissue within and under the foliate papillae contains serous glands (von Ebner’s glands) that open via ducts into the cleft between neighboring papillae. 45. d. Circumvallate papillae are covered by stratified squamous epithelium that may be slightly keratinized. Each circumvallate papilla is surrounded by a trench or cleft. Numerous taste buds are on the lateral walls of the papillae. The dorsal surface of the papilla is smooth. The deep trench surrounding the circumvallate papillae and the presence of taste buds on the sides rather than on the free surface are features that distinguish circumvallate from fungiform papillae. The connective tissue near the circumvallate papillae also contains many serous-type glands that open via ducts into the bottom of the trench. 25.