The rhinarium of lagomorphs is similar in detail to that of rodents. It consists of narial pads situated between the nares. Each pad consists of two crurae and the pads are separated from the Dorsum nasi by the Sulcus transversarius. Moreover, the ontogenetic process of pad formation is much the same in both orders. The Regio rhinarica is first a single structure, i.e., undivided, which becomes subdivided by increasing isolation of the pads within the Regio internarica. Distributional data suggest that the undivided Regio rhinarica in adult stages is a plesiomorphic mammalian and therian character. Most probably, the undivided common type rhinarium with developed internaric, supralabial and supranaric parts as well as Sulcus medianus and Areolae rhinarii is also a therian groundplan character. Cohesion of the Regio rhinarica throughout ontogeny is widespread within therians and the formation of pads, i.e., subdivision of the Regio rhinarica, is most likely nested within the large sample of taxa showing the undivided condition during ontogeny. Thus, application of the ontogenetic criterion indicates that narial pads of rodents and lagomorphs are an apomorphic therian character. Ontogenetic criterion and comparison with monotremes. metatherians and metatherian groundplan give mutual support that the narial pads are an autapomorphic character of the Glires. Evidence from behavior, neurology, and morphology suggest, that the evolution of pads was part of a complex evolutionary transformation. The primitive rhinarium, originally an extended skin area providing a tool for tactile exploration and manipulation, has been reduced to the comparatively small narial pads. The gnawing teeth, easily exposable, seem to have replaced the rhinarium in that regard. Associated with the gnawing apparatus, infoldings of the lips (Inflexa pellita) have separated the gnawing teeth from the remaining toothrow. A median cleft of the lip allows easy exposure of the incisors antertiorly. The uniqueness of the narial pads and their likewise unique ontogeny within Recent mammals as well as their involvement into a complex evolutionary transformation, supports the hypothesis of Glires monophyly. Other seemingly unique external characters of rodents and lagomorphs corroborate this conclusion (Inflexa pellita, highly mobile Dorsum nasi).