The dorsal surface of the tongue is covered with four types of papillae. Filiform are the most numerous papillae and cover the anterior two-thirds of the dorsum of the tongue. Although these papillae have no taste function, they may serve a tactile function. There are four basic taste sensations: sweet, salt, sour, and bitter. Specific regions of the tongue have specific associations with these sensations. The data is incomplete, but it's been shown that generally the tip of the tongue has receptors for sweet and salty sensation, and sour and bitter receptors lie near the back.
Fungiform papillae are singular knoblike projections scattered among the filiform papillae and may appear redder than the area around them. Circumvallate papillae are large, mushroom-shaped elevations that form an inverted V separating the anterior two-thirds from the posterior one-third of the tongue.
Foliate papillae are found on the lateral border of the tongue in the region of the circumvallate papillae and appear as parallel slits.