The Wart Hog has a very anomalous dentition, for as age advances all the teeth except the canines and last molars show signs of disappearing; both pairs of persisting teeth are however very large. Various extinct Ungulata such as _Anoplotherium_ have teeth which are intermediate in character between the bunodont and selenodont types. _Anoplotherium_ has the regular mammalian series of forty-four teeth. The crowns of all the teeth are equal in height, and there is no diastema--an arrangement found in no living mammal but man. We come now to the selenodont Artiodactyla. The Tylopoda--camels (Camelidae) and Llamas (Aucheniidae) when young have the full number of incisors, but in the adult the two upper middle ones are lost. The molars are typically selenodont and hypsodont[158]. In the Camel the dental formula is _i_ 1/3 _c_ 1/1 _pm_ 3/2 _m_ 3/3, total 34. The upper incisors, canines and first premolars of the Camel are very small teeth, and the first premolar is separated by a long diastema from the others. The Tragulina or Chevrotains have no upper incisors, while the canines are largely developed, especially in the male. The Ruminantia or Pecora are very uniform as regards their dentition. The upper incisors are always absent, for though their germs are developed they are reabsorbed without ever becoming visible, and as a rule the upper canines are absent too, while the lower canines are incisiform. The grinding teeth are typically selenodont, and in the lower jaw form a continuous series separated by a wide diastema from the canines. The dental formula is usually _i_ 0/3 _c_ 0-1/1 _pm_ 3/3 _m_ 3/3. The canines are largely developed in the male Muskdeer (_Moschus_) and in _Hydropotes_. _PERISSODACTYLA_. The premolars and molars have a very similar structure and form a continuous series of large square teeth with complex crowns. The crowns are always constructed on some modification of the bilophodont[159] plan, as is easily seen in the case of the forms with brachydont teeth, but in animals like the Horse, in which the teeth are very hypsodont, this arrangement is hard to trace. All four premolars in the upper jaw are preceded by milk teeth, while in Artiodactyla the first has no milk predecessors. In the Tapiridae the grinding teeth are brachydont and the lower ones are typically bilophodont. The last two upper molars have the transverse ridges united by an outer longitudinal ridge. The dentition is _i_ 3/3 _c_ 1/1 _pm_ 4/3 _m_ 3/3, total 42. In some of the extinct Perissodactyles such as _Lophiodon_[160], the dentition is brachydont and bilophodont, the grinding teeth in general resembling the posterior upper molars of the Tapir. The same type of brachydont tooth is seen in _Palaeotherium_ but the transverse ridges are crescentic instead of straight, and are separated from one another by shallow valleys without cement. Some of the Palaeotheridae have the regular series of forty-four teeth.