_i_ 1/1 _c_ 0/0 _pm_ (0--1)/(0--1) _m_ 3/3, total 18 or 20. The incisors always have chisel-like edges and persistent pulps, and are separated by a wide diastema from the premolars. Canines are always absent, and there are generally three grinding teeth not preceded by milk teeth; their surface may be grooved, or may be bunodont. Teeth are most numerous in the Duplicidentata (Hares and Rabbits), in which the formula is _i_ 2/1 _c_ 0/0 _pm_ 3/2 _m_ 3/3, total 28, and fewest in Hydromys and certain other forms, in which the formula is _i_ 1/1 _c_ 0/0 _pm_ 0/0 _m_ 2/2, total 12. The hares and rabbits are the only rodents which have well developed deciduous incisors, though a vestigial milk incisor has been described in the Mouse (_Mus musculus_). The last upper molar of _Hydrochaerus_ is very complicated, its structure approaching that of the teeth of Elephants. [Illustration FIG. 84. CARNASSIAL OR SECTORIAL TEETH OF CARNIVORA (from FLOWER). _Upper sectorial teeth_ of I. _Felis_, II. _Canis_, III. _Ursus_. 1. anterior, 2. middle, 3. posterior cusp of blade, 4. inner lobe supported on distinct root, 5. inner lobe posterior in position and without distinct root, characteristic of the Ursidae. _Lower sectorial teeth._ 1. _Felis_, 2. _Canis_, 3. _Herpestes_. 1. anterior, 2. posterior lobe of blade, 3. inner tubercle, 4. heel.] CARNIVORA have the teeth rooted and markedly diphyodont and heterodont. The canines are greatly developed, and the incisors are small. In _CARNIVORA VERA_ the incisors are almost always 3/3. The fourth upper premolar and first lower molar are differentiated as carnassial teeth (see p. 436), and retain fundamentally the same characters throughout the suborder. The upper carnassial (fig. 84, I. II. III.) consists of a more or less compressed, commonly trilobed blade borne on two roots, with an inner tubercle borne on a third root. The lower carnassial has only two roots; its crown consists of a bilobed blade with generally an inner cusp, and a heel or talon (fig. 84, 4) behind the blade. The most thoroughly carnivorous type of dentition is seen in the Æluroidea, and especially in the cat tribe (Felidae). In the genus _Felis_ the dental formula is _i_ 3/3 _c_ 1/1 _pm_ 3/2 _m_ 1/1, total 30. The incisors are very small, so as not to interfere with the action of the large canines, the lower carnassial is reduced to simply the bilobed blade (fig. 84, IV), and the cheek teeth are greatly subordinated to the carnassial. The extinct _Machaerodus_ has the upper canines comparable in size to those of the Walrus. The Civets and Hyaenas have a dentition allying them closely to the cats. The hyaena-like _Proteles_ has, however, the grinding teeth greatly reduced.