. The comparative anatomy of the domesticated animals. Veterinary anatomy. 354 THE DIGESTIVE APPABATUS IN MAMMALIA been worn, this frictional surface assumes a particular aspect, which will ha indicated with most advantage to the student by examining the structure of the molar. " The root, if examined a short time after the eruption of the free portion, looks only like the shaft of the latter, without any appear- ance of'fangs, and has internally a wide cavity. It is not until the tooth begins to be pushed from the alveolus and its crown to become worn, that its fangs are formed; these ar
. The comparative anatomy of the domesticated animals. Veterinary anatomy. 354 THE DIGESTIVE APPABATUS IN MAMMALIA been worn, this frictional surface assumes a particular aspect, which will ha indicated with most advantage to the student by examining the structure of the molar. " The root, if examined a short time after the eruption of the free portion, looks only like the shaft of the latter, without any appear- ance of'fangs, and has internally a wide cavity. It is not until the tooth begins to be pushed from the alveolus and its crown to become worn, that its fangs are formed; these are at first hollow, and afterwards filled, as well as the cavity of the tooth, by the formation of a new quantity of dentine. From this time the fangs cease to grow; but the tooth, constantly projected beyond the alveolar cavity, allows the walls which inclose it to contract; so that, in extreme old age, it happens that the shaft, completely worn away, instead of the tooth, leaves several stumps formed by the fangs. " The molars of the two jaws exhibit a variety of roots. In the molars terminating the arcades, either above or below, or at the extremities of these, there are three; while the intermediate molars have four fangs in the upper jaw, and only two in the lower. " The molars are separated from each other by theix imbedded portion, particularly at the two extremities of the arcade; an arrangement which strengthens them by throwing the strain put upon the terminal teeth towards the middle of the ; The structure of the molars resembles that of the incisors, though it is much more complicated. The internal cavity is extremely diverticulated, and enveloped by the dentine. The ejiamel is applied in a layer over it, and is doubled in its external culs-de-sac exactly as in the incisors. There is also on the table of the tooth which has been worn, an external covering of enamel, and two circles, or rather two irregular polygons, of central enamel circumscribin
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