. Elements of zoölogy : a textbook. Zoology. 124 VERTEBRATA : MAMMALIA. FIG. The Rodents are readily distinguished by their teeth. In each jaw they have two chisel-shaped incisors, between which and the molars there is a wide space without teeth, ca- nines being wanting. The incisors are covered with enamel only in front, so that their posterior edges wear away ami teeth oi a faster than the anterior edges, thus al- ways keeping these teeth sharp, however much they are used ; and they grow at the base as fast as they wear away at the summit. The lower jaw is articulated with the skull in
. Elements of zoölogy : a textbook. Zoology. 124 VERTEBRATA : MAMMALIA. FIG. The Rodents are readily distinguished by their teeth. In each jaw they have two chisel-shaped incisors, between which and the molars there is a wide space without teeth, ca- nines being wanting. The incisors are covered with enamel only in front, so that their posterior edges wear away ami teeth oi a faster than the anterior edges, thus al- ways keeping these teeth sharp, however much they are used ; and they grow at the base as fast as they wear away at the summit. The lower jaw is articulated with the skull in such a manner that the jaws have no hori- zontal motion, except backwards and forwards as is requi- site in the act of gnawing. The enameled ridges of the molars are transverse, thus in opposition to the horizontal forward and backward motion of the jaw, and exactly adapted to the process of trituration. The form of the Uodentia is generally such that the hind parts consider- ably exceed the forward parts; most kinds are thus adapt- ed to leaping instead of walking. The brain of the Rodents is smooth (Fig. 66), that is, without convolutions. Some kinds of the Rodentia, as the Jerboas or Dipodidre FIG. 130. Fro. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Tenney, Sanborn, 1827-1877. New York : Scribner
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