Circumvallate papilla on tongue. Coloured Scanning Electron Micrograph (SEM) of the surface of mammalian tongue, showing a circumvallate (round) papilla. The papilla is seen at above centre. It is surrounded by small, pointed filiform papillae, much the more numerous type of papillae which make the tongue feel rough. Circumvallate papillae are the largest and rarest of three types of tongue papillae. They consist of the papilla itself, a wall surrounding it, and an intervening moat" or trench. In this moat large numbers of taste buds occur; circumvallate papillae play an important role in taste. They are found at the back of the tongue. Magnification: x52 at 6x7cm size. x176 at 8x10 inch size."