Tongue surface. Light micrograph of a section through the surface of a tongue showing a circumvallate papilla (round, upper left), one of the structures that controls the sense of taste. The papilla is set into the surface of the tongue and surrounded by a cleft (narrow white channel). The epithelial lining of the cleft contains numerous taste buds (round, light purple), sensory structures stimulated when food dissolves in the mouth. Aggregations of glands, known as Von Ebner's glands (light purple clumps, lower frame), secrete watery fluid into the cleft. This helps to dissolve food components, aiding taste. Magnification unknown.