ネズミ類の臼歯の型と発育について : II.長歯性臼歯

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1. The present paper reports the result of observations on developmental processes of the hypsodont molars in the two species of microtine vole, Clethrionomys rufocanus bedfordiae and Microtus montebelli. 2. The first and second molars of the two species begin to develop in the embryonic period and erupt on about 10th day after birth. In Microtus, however, there seems to exist some individuals whose molars erupt a few days earlier. Upper surface of the crown begins to wear out as soon as the upper and lower molars come into contact. 3. The modes of development of the molars in these two species are quite similar during at least 30 days after birth. The height of the dental crown increases gradually, and its bending, so characteristic of each molar, becomes more remarkable at the same time. 4. In Microtus the dental development of this feature lasts through life; in Clethrionomys the dental roots begin to appear after reaching adult stage, and since that time the height and length of the teeth begin to decrease. Each molar develops only two roots. 5. The dental roots of hypsodont molars in Clethrionomys differ from those of brachyodont teeth: they have, for instance, no cement layer around the dentine and continue to grow compensating the wearing down of the crown. 6. From the facts mentioned above and a fact that the prototype of mammalian teeth is brachyodont, it may be said that the hypsodont molars in Microtus, which bear no root, represent an extremely specialized type and that those in Clethrionomys, which develop the roots in the adult stage, represent a less specialized type in subfamily Microtinea.
社団法人日本動物学会の論文
1962-03-15

ネズミ類の臼歯の型と発育について : II.長歯性臼歯

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