The tongue is a muscular hydrostat on the floor of the mouth of most vertebrates that manipulates food for mastication. It is the primary organ of taste (gustation), as much of its upper surface is covered in taste buds. The tongue's upper surface is also covered in numerous lingual papillae. It is sensitive and kept moist by saliva, and is richly supplied with nerves and blood vessels. In humans a secondary function of the tongue is phonetic articulation. The tongue also serves as a natural means of cleaning the teeth. The ability to perceive different tastes is not localised in different parts of the tongue, as is widely believed. This error arose because of misinterpretation of some 19th-century research (see tongue map).