DIGESTION. 51 



each jaw. In each jaw there are 4 incisors, 2 canines, and 4 molars. 

 When the milk teeth drop out they are followed by the permanent 

 teeth. 



The permanent teeth are 32 in number, 16 in each jaw, consisting 

 of 4 incisors, 2 canines, 4 bicuspids, and 6 molars. 



There are three distinct parts in a tooth : crown, root, and neck. 



The crown, or body, is the protruding portion of the tooth; the 

 portion inserted in the alveolus of the jaws is the root, or fang. The 

 slightly constricted part enveloped by the gum, is the neck. The fang 

 is firmly fastened to the sides of the alveolus, in which it is inserted 

 by fibrous tissue, which is continuous with the periosteum of the jaws. 

 When the jaws are closed the under incisors are inclosed by the upper 

 ones, but the grinding surfaces of the molars are in contact. 



Temporary Teeth. There are 20 milk teeth, 10 in each jaw, or 

 5 on each side of the jaw; that is, 2 incisors, 1 canine, and 2 molars. 

 The temporary set resembles the permanent in form and structure. 

 The teeth are, however, fewer in number, smaller in size, and charac- 

 terized by the bulging out of the crown close to the neck, making the 

 latter very sharply defined. Lower central incisors are the first to 

 appear. They appear about the seventh month. 



The milk teeth die off and so give room for the second and more 

 permanent set. They die partly in accordance with the rule of epi- 

 thelial tissues and drop off, since all such tissues are expelled after 

 their death ; then, too, the jaws grow as the being passes from infancy 

 to adult life, when larger and more numerous teeth must replace the 

 smaller ones, so as not to impair the efficiency necessary to masticate 

 quantities of food proportionate to the demands of the growing body. 



Permanent Teeth. They are 32 in number. There are 8 in- 

 cisors and they form the 4 front teeth in each jaw, and are named 

 incisors because they divide the food. The upper incisors are the 

 larger. The lower molar is the first to appear in the permanent 

 set. It appears about the sixth year. 



The canine teeth are 4 in number, larger than the incisors. The 

 upper canines are usually called the eye teeth, and they are longer 

 and larger than the canine teeth in the lower jaw. In the carnivorous 

 animals, like the dog, the canine teeth are usually large; hence the 

 name of canine. The lower canines are popularly known by the name 

 of stomach teeth. There are 4 premolars, or bicuspids, in each jaw. 

 They* are shorter and smaller than the canines. The bicuspids of the 

 upper jaw are larger than those of the lower jaw. The functions of 

 the bicuspids are to cut and grind the food. The molars are 12 in 



