The Teeth.

THE teeth are not like other bones, either in composition, method of nutrition, or growth. When broken they do not unite, not being furnished with the necessary power of reproduction of lost parts.
Both the upper and lower teeth are set into bony sockets, called alveolar processes. These, with the fibrous gums, give the teeth a very firm setting.

Origin. The teeth have their origin in little membranous pouches within the bone of the jaw, which, in their interior, have a fleshy bud. From the surface of this the bone or ivory exudes. The tooth and the bony socket are developed and rise up together, the former, when sufficiently long, pushing itself through the gum.

Number. The first set of teeth are only temporary, and are called milkteeth. There are but twenty of them. Between the age of six and fourteen, these become loose, and drop out, and the permanent teeth appear in their places. Of these there are thirty~two, sixteen in each jaw.

Names. The four front teeth in each jaw, a, 6, Fig. 27, are the cutting teeth (incisors) ; the next one, e, is an eyetooth (cuspid); the next two, c7, e, are small grinders (bicuspids) ; the last three, f, g, 7&,are grinders (molars). One appears late on each side, from the apof twenty to twentyfour, and is called wisdom tooth.

Composition. A tooth is composed of ivory ancl enamel. The internal part is ivory, which is harder than bone. The, coating upon the surface is enanwl, which is still harder than ivory. That part which rises above the jawbone is called the crown; it is this only which is covered with enamel. The part within the jaw is called the root orfang; this is composed of bony matter, through which small vessels pass in to nourish the tooth. Small white nerves also paw into the tooth, of the presence of which we have terrible evidence in toothache.