. The Cambridge natural history. Zoology. 460 INCISOR AND MOLAR TEETH grow to a very great length, extending back within the jaw to near the hinder part of the skull. These teeth are reinforced in tlie upper jaw by a small second pair in the Lagomorpha only. The incisors are chisel-shaped, and often brown or yellow upon the outer face, as is the case also with some Insectivores. This peculiar shape, and their strength, renders them especially capable of the gnawing action which characterises the Eodents. It has been pointed out that where the incisors are wider than thick, the gnawing powers a
. The Cambridge natural history. Zoology. 460 INCISOR AND MOLAR TEETH grow to a very great length, extending back within the jaw to near the hinder part of the skull. These teeth are reinforced in tlie upper jaw by a small second pair in the Lagomorpha only. The incisors are chisel-shaped, and often brown or yellow upon the outer face, as is the case also with some Insectivores. This peculiar shape, and their strength, renders them especially capable of the gnawing action which characterises the Eodents. It has been pointed out that where the incisors are wider than thick, the gnawing powers are feebly developed; and that on the con- trary, where these teeth are thicker than wide, the animals are good gnawers. The incisors have often an anterior groove, or it may be Fig. 232.âMolar teeth of Rodents. A, of C'lipybara (Hijdrochoerus) ; B, of Squirrel (Scivnis) â C, of riciiii,/âcfi//iii (After TiiUberg.) The cheek teeth vary in number from two {Hydromys) to .six (Eabbit) on each side of the two jaws. Four is the prevailing number outside the large division of the Itat-like Eodents. They are often set at an angle to the horizontal plane of the jaw, looking outwards and obliquely to its longitudinal axis; the in- dividual teeth too are not unfrequently bowed in form, remind- ing us of those of TiKCdilvn. This of course only occurs in those genera which have hypselodont teeth. The pattern of the teetli varies much, and the different forms recall the teeth of more than one other group of mammals. They are either bunodont or lophodont. In many cases the tooth is encircled with a ridge of enamel, which is either almost simple or has a more com- plicated contour ; such teeth are )jy no means unsuggestive of the Toxodonts. Some of the lophodont molars are by no means unlike those of the Proboscidea. In ,S'ciurns vulgaris the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
