. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. RODENTIA. 385 osteum, which covered the portion of bone absorbed from the bottom of the alveolus. The jumping hare (Hclamys capensis), when full grown, offers a good example of this cu- rious structure. The molars are not numerous in any Ro- dents ; the hare and rabbit (Lepus) have g g ——- ; i. e. six molars on each side of the upper 5—3 jaw, and five on each side of the lower jaw: 5 5 the pika (Lagomys), has '-—- ; the squirrels have 5—5 5—5 ; the families of the dormice, the 4—4 porcupines, the spring rats (Ec/tingideu
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. RODENTIA. 385 osteum, which covered the portion of bone absorbed from the bottom of the alveolus. The jumping hare (Hclamys capensis), when full grown, offers a good example of this cu- rious structure. The molars are not numerous in any Ro- dents ; the hare and rabbit (Lepus) have g g ——- ; i. e. six molars on each side of the upper 5—3 jaw, and five on each side of the lower jaw: 5 5 the pika (Lagomys), has '-—- ; the squirrels have 5—5 5—5 ; the families of the dormice, the 4—4 porcupines, the spring rats (Ec/tingideu), the octodonts, chinchillas, and cavies, have 4 4, f molars; in the great family of rats rr —4< (Jlftcne&e), the normal number of molars is O o o^^ i but the Australian water rat (Hydro- 2 2 myg) has but — ~ molars, making with the £' ' & incisors twelve teeth, which is the smallest number in the Rodent order ; the greatest number of teeth in the present order is twenty- eight, which is exemplified in the hare and rabbit ; but thirty-six teeth are developed in these species, six molars and two incisors being deciduous. In all the Rodents, in which the number of molars exceeds three in a series, the addi- tional ones are anterior to these, and are pre- molars, i. e. they have each displaced a deci- duous predecessor in the vertical direction, and are what Cuvier calls dents de remplace- ment. This it is which constitutes the essential distinction between the dentition of the marsupial and the placental Rodent; the latter, like the placental Carnivora, Ru- minantia, and ordinary Pachydermata having never more than three true molars. Thus the Rodents, which have the molar formula of 4 4, —r, shed the first tooth in each series ; and 41—*r this is succeeded by a permanent pre-molar, which comes into place later than the true molars; later, at least, than the first and second, even when the deciduous molar 1st shed before birth, as was observed b
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