THE DIGESTIVE SYSTEM 



159 



The Teeth. The teeth are thirty-two in number. 

 There are sixteen in each jaw, divided into four incisors, 

 or cutting teeth, two canines, four bicuspids, and six 

 molars, or grinding teeth. Each tooth consists of a 

 crown, covered with enamel, a neck, and a root, sur- 

 rounded by the crusta petrosa, a thin layer of bone, em- 



FlG. 78.. Schema showing the temporary and permanent teeth in a child 

 five years old (right side) : i, Temporary teeth of the upper jaw ; 2, the five 

 temporary teeth of the lower jaw ; 3, 3', permanent median incisors; 4, 4', 

 permanent lateral incisors ; 5,5', permanent canines ; 6, 6', the' four perma- 

 nent bicuspids; 7, 7', first molar; 8, second molar of lower jaw in its alveo- 

 lus (in the upper jaw the second molar is not yet formed) ; 9, inferior dental 

 canal ; 10, orifice of inferior dental canal (after Testut). 



bedded in the alveolar process formed by the jaw bones. 

 A section through a tooth shows that it is composed of 

 dentine, in the center of which is the pulp cavity, contain- 

 ing blood-vessels and nerves. 



Temporary Teeth. The temporary teeth of children 

 are twenty in number ten upper and ten lower. They 

 appear at about the following ages, the lower teeth usually 



