. Texte livre de zoologie. Zoologie. La classe 6. Mammalia. 483 Il peut être faible et large^ fournis witli arrondie ou pointue des tubercules, ou il peut être bien compressé et dentelée à l'extrémité ; ou encore, il peut être traversé par de fortes crêtes transversales ou longitudinales séparées par des vallées, qui peut être si profond que pour atteindre la base de la Couronne (p. ex., dans les molaires de l'éléphant). Sillons perpendiculaires peuvent également se produire sur les côtés des dents ; habituellement, les plis plus profonds sont partiellement ou complètement rempli avec du ciment (chez le cheval et l'éléphant). Au cours de l'utilisation, l'émail, en particulier dans les dents plissées, est ve

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. Text book of zoology. Zoology. Class 6. Mammalia. 483 it may be low and broad^ provided witli rounded or pointed tubercles, or it may be much compressed and serrate at the edge ; or again, it may be traversed by marked transverse or longitudinal ridges separated by valleys, which may be so deep as to reach the base of the crown {e.g., in the molar teeth of the Elephant). Perpendicular furrows may also occur on the sides of the teeth ; usually the deeper folds are partially or completely filled with cement (in the Horse and Elephant). During use, the enamel, especially in plicate teeth, is very frequently worn away at all the projecting points, and the subjacent dentine is thus laid bare ; at the grinding surface, therefore, may be seen islands of dentine surrounded by slightly elevated enamel borders, and the latter are often again surrounded by cement (especially in teeth of herbivorous animals). The crowns and roots of many teeth are of almost equal length; sometimes one, sometimes the other may, however, be the longer. The former especially the case with much folded teeth, which are subjected to considerable wear and tear; in these the root (or roots) is often very short; the crown, on the contrary, is very long, but it projects from the jaw for only part of its length, and gradually, as the free end is worn away, the tooth is pushed out {e.g., in the molars of the Horse). The crown has often begun to wear down before the root is formed; in other cases tbere is actually no development of a root; as the crown is worn away above, growth takes place below, and never ceases; such teeth are said to grow from persistent pulps (the incisors of E.odents, the molars of many of the same group, the canines of the Boar, etc.). The teeth are arranged in a single row along the edge of premaxilla, maxilla, and mandible; those of designated incisors, the anterior teeth of the maxilla, next to these, canines; the rest, molars; in the lower jaw the teeth which bite just in front

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• bookdecade1890
• booksubjectzoology
• bookyear1896