rodentia

Century Dictionary and Cyclopedia

1. An order of ineducabilian placental diphyodont Mammalia; the gnawers. The brain has a relatively small cerebrum, leaving much of the cerebellum and olfactory lobes exposed, and the corpus callosum has no well-defined rostrum in front. The placentation is discoidal-deciduate. The limbs are ambulatorial, variously modified for running, leaping, climbing, or swimming. The condyle of the lower jaw has its long axis longitudinal, and is not confined in a special socket, but glides back and forth, so that the lower jaw can be put forward and backward as well as moved up and down. The molar teeth are typically ridged on their crowns in various patterns; they are nearly always 3 in nnmber above and below on each side. The premolars are small or few, often none. There are no canines. The incisors are large, strong, heavily enameled on their front surface, scalpriform or beveled to a sharp edge, and grow continually from persistently open pulps; their roots traverse much or nearly all of the bones of either jaw, in the arc of a circle. The typical number of incisors is 2 above and below, or one pair of upper and under front teeth; exceptionally, as in the rabbit tribe, there are small supplementary upper incisors, crowded together and concealed behind the functional pair. In some groups, as Arvicolinæ, the molar teeth are perennial, like the incisors. There being no canines, and the premolars being few and small, if any, there is a great gap between the front and the back teeth. The typical number of teeth is 16, which obtains with few exceptions throughout the murine series of rodents; in one genus there are only 12. In the hystricine series there are normally 20 teeth, in one genus 16. In the sciurine series the teeth are always either 20 or 22; in the leporine series there are 26 or 28. This order is by far the largest one among mammals, and of world-wide distribution; its numerous members are adapted to every kind of life. They are mostly of small size, a rabbit being far above the average; the beaver, porcupine, or coypou is a very large rodent, and the capibara is a giant. The order is divisible into 3 suborders: Hebetidentata, enormal or blunt-toothed rodents, exceptional in having 4 lower incisors, and extinct; Duplicidentata, subnormal or double-toothed rodents, with 4 upper incisors: these are the hares, rabbits, and pikas; and Simplicidentata, normal or simple-toothed rodents, with only 2 incisors above and below. The last fall in 3 series: Hystricomorpha, the hystricine series, including the porcupines and very numerous related forms, chiefly South American, as the capibara, coypou, cavies, viscachas, chinchillas, octodonts, etc. (see cuts nnder capibara, coypou, rabbit-squirrel, porcupine, and Plagiodon); Myomorpha, the murine series, including rats and mice of all kinds (see cuts under mouse, Muridæ, and rice-field); and Sciuromorpha, the sciurine series, or the squirrels, spermophiles, marmots, beaver, etc. (see cuts under Arctomys, beaver, and prairie-dog). In addition, the duplicident rodents are Lagomorpha, the leporine series, the same as the suborder Duplicidentata, (See cut under Lagomys.) Many fossils of all these groups are known. There are 20 or 21 families of living rodents, and 100 genera. The order corresponds to the Linnean Glires, and is still often called by that name. Also called Rosores. See cuts under castor, Leporidæ, and scalpriform.

GNU Webster's 1913

1. n. (Zoöl.) An order of mammals having two (rarely four) large incisor teeth in each jaw, distant from the molar teeth. The rats, squirrels, rabbits, marmots, and beavers belong to this order.

WordNet 3.0

1. n. small gnawing animals: porcupines; rats; mice; squirrels; marmots; beavers; gophers; voles; hamsters; guinea pigs; agoutis.