Chemotopic representation of the human tongue according to Hänig (1901), the first source on tongue maps,
showing that no taste area is sensitive to less than 4 taste qualities. Taste sensitivity (inverse detection threshold)
is represented by the density of symbols. For each of the 4 qualities shown, sensitivity extends across anterior,
lateral and posterior (vallate) parts of the tongue. It is highest for sucrose-sweet at the tip, for HCl-sour at the
sides and for quinine-bitter at the back, but the differences in sensitivity within each quality are moderate
(they are also controversial). In addition, taste sensitivity was reported for the palate (not included here).

From these diagrams, now 98 years old, the popular textbook versions, often conveying the impression of
more or less specialized areas, probably arose by "graphical evolution", a curious process.

The chemotopic diagram of a rat tongue was never published. It would look quite different from the human
diagram, but in the rat, too, areas are not specialized to a single taste quality.