TEETH

are the organs of mastication, grinding down the food so that it can be easily swallowed. Situated in the upper and lower jaws, they are developed not from bone but from the same ti ue as the dermis, or true skin. The body of a tooth is formed of a somewhat hard substance termed dentine, composed of minute tubules, containing earthy matter closely cked together; the dentine body is hollow, the cavity being termed the pulp cavity, and containing arteries, veins, and a branch of a nerve which supplies the tooth. Covering the dentine in the region of the root of the tooth, contained within the gum, is a layer of cement, which protects the lower part of the body; while covering the body towards the crown, outside the gum is a layer of enamel, the hardest ti ue in the human body, composed almost entirely of earthy matter, enabling the tooth to carry out its functions effectively. The different types of teeth are adapted for different purposes; the ¢neisors, for cutting the food, have a single root and a somewhat thin vertical crown, which is beveled behind so as to present a sharp cutting edge; the canines, for tearing, are highly developed in carnivorous animals such as the dog, and have a single deep root and a rounded, pointed crown; the premolars or bicuspids have single or sometimes two roots, and a rather square crown on which are two slight projections; the molars, with the premolars, for grinding down the food, are much larger than the other teeth, and have from two to five roots, which are comparatively short, square crowns, on which are from three to five slight projections er cusps. A child has only twenty teeth, termed ‘milk teeth,’ which begin to appear at the age of six months and persist till about the age of seven years, when they fall out and begin to be replaced by the permanent teeth. An adult has 32 teeth, comprising, in each half of each jaw, 2 incisors, 1 canine, 2 premolars, and 3 molars. The most common disease of the teeth is caries, consisting of a progre ive decay of the substance of a tooth, predisposed to by hereditary weakne in the ti ues of the tooth substance, by debilitated conditions, disorders of the digestive system, or neglect and consequent retention of putrefying particles of food between the teeth; caries has been shown to be caused by a microorganism, and should at once be treated by a properly qualified dentist. See DENTISTRY. town, Arcadia, ancient Greece; contain a remains of famous temple of Athens Alea, built by Scopas; frequently engaged in warfare against Sparta; eventually destroyed by Alaric. lake, Upper Bavaria; drained by Mangfall to the Inn; length, 4 miles.