This figure shows the dorsal surface of the tongue with the filiform papillae (Fil P). They are the most numerous of the three types of papillae. Structurally, they are bent, conical projections of the epithelium, with the point of the projection directed posteriorly. These papillae do not possess taste buds and are composed of stratified squamous keratinized epithelium. The fungiform papillae are scattered about as isolated, slightly rounded, elevated structures situated among the filiform papillae. A fungiform papilla is shown in the inset. A large connective tissue core (primary connective tissue papilla) forms the center of the fungiform papilla, and smaller connective tissue papillae (secondary connective tissue papillae) project into the base of the surface epithelium (arrowhead). The connective tissue of the papillae is highly vascularized. Because of the deep penetration of connective tissue into the epithelium, 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.
Ventral surface, tongue, monkey, H&E ×65.
The ventral surface of the tongue is shown in this figure. The smooth surface of the stratified squamous epithelium (Ep) contrasts with the irregular surface of the dorsum of the tongue.
Moreover, the epithelial surface on the ventral surface of the tongue is usually not keratinized. The connective tissue (CT) is immediately deep to the epithelium; deeper still is the striated muscle (M).
The numerous connective tissue papillae that project into the base of the epithelium of both ventral and dorsal surfaces give the epithelial– connective tissue junction an irregular profile. Often, these connective tissue papillae are cut obliquely and then appear as small islands of connective tissue within the epithelial layer (see figure above).
The connective tissue extends as far as the muscle without changing character, and no submucosa is recognized. The muscle (M) is striated and is unique in its organization; i.e., the fibers travel in three planes. Therefore, most sections will show bundles of muscle fibers cut longitudinally, at right angles to each other, and in cross section. Nerves (N) that innervate the muscle are also frequently observed in the connective tissue septa between the muscle bundles.
The surface of the tongue behind the vallate papillae (the root of the tongue) contains lingual tonsils (not shown). These are similar in structure and appearance to the palatine tonsils illustrated in Plate 36.
KEY CT, connective tissue Ep, epithelium Fil P, filiform papillae M, striated muscle bundles N, nerves arrowhead (inset), secondary connective tissue papilla