THE TEETH [Footnote: Although the teeth are always found in connection with the skeleton, and are, therefore, figured as a part of it (Fig. 1), yet they do not properly belong to the bones of the body, and are merely set in the solid jaw to insure solidity. They are hard, and resemble bony matter, yet they are neither true bone nor are they formed in the same manner. "They are properly appendages of the mucous membrane, and are developed from it."--LEIDY. "They belong to the Tegumentary System, which, speaking generally of animals, includes teeth, nails, horns, scales, and hairs."--MARSHALL. They are therefore classed with the mucous membrane, as are the nails and hair with the skin.] are thirty-two in all,--there being eight in each half jaw, similarly shaped and arranged. In each set of eight, the two nearest the middle of the jaw have wide, sharp, chisel-like edges, fit for cutting, and hence are called _incisors_. The next one corresponds to the great tearing or holding tooth of the dog, and is styled the _canine_, or eye-tooth. The next two have broader crowns, with two points, or cusps, and are hence termed the _bicuspids_. The remaining three are much broader, and, as they are used to crush the food, are called the _grinders_, or _molars_. The incisors and eyeteeth have one fang, or root; the others have two or three fangs. THE MILK TEETH.--We are provided with two sets of teeth. The first, or milk teeth, are small and only twenty in number. In each half jaw there are two incisors, one canine, and two molars. The middle incisors are usually cut about the age of seven months, the others at nine months, the first molars at twelve months, the canines at eighteen months, and the remaining molars at two or three years of age. The lower teeth precede the corresponding upper ones. The time often varies, but the order seldom. THE PERMANENT TEETH.--At six years, when the first set is usually still perfect, the jaws contain the crowns of all the second, except the wisdom teeth. About this age, to meet the wants of the growing body, the crowns of the permanent set begin to press against the roots of the milk teeth, which, becoming absorbed, leave the loosened teeth to drop out, while the new ones rise and occupy their places. [Footnote: If the milk teeth, do not promptly loosen on the appearance of the second set, the former should be at once removed to permit the permanent teeth to assume their natural places. If any fail to come in regularly, or if they crowd the others, a competent dentist should be consulted.] FIG. 25. [Illustration: _The teeth at the age of six and one half years._ I, _the incisors;_ O, _the canine;_ M, _the molars; the last molar is the first of the permanent teeth;_ F, _sacs of the permanent incisors;_ C, _of the canine;_ B, _of the bicuspids;_ N, _of the second molar; the sac of the third molar is empty._-- MARSHALL.]