Rodents (Rodentia=:11 gnawing animals"), a well-defined order of Mammals, more widely distributed, and containing a greater number of species, than any other, and easily recognised by their large chisel-shaped incisor teeth and the absence of canines. All of them gnaw their food; nearly all are vegetable-feeders, but mice and rats are omnivorous. Most of them are adapted for life on the ground, but some are arboreal, others burrow, and a few are aquatic. There are two sub-orders - (1) Simple-toothed Rodents (Simplicidentata), with two upper incisors, and (2) Double-toothed Rodents (Duplicidentata), with a second pair of small size immediately behind the functional incisors of the upper jaw. Rats and mice belong to the first, and haree and rabbits to the second, group.