166 DIGESTION 



4. Twelve molars, or multicuspid, situated just back of the bicuspid ; 

 six in each jaw. 



The incisors are wedge-shaped, flattened antero-posteriorly, and 

 bevelled at the expense of the posterior face, giving them 'a sharp 

 cutting edge. Each incisor has a single root The permanent incisors 

 make their appearance between the seventh and the eighth years. 



The canines are more conical and pointed than the incisors, and 

 have longer and larger roots, especially those in the upper jaw. Their 

 roots are single. The permanent canines make their appearance 

 between the eleventh and the twelfth years. 



The bicuspid teeth are shorter and thicker than the canines. Their 

 opposed surfaces are rather broad and are marked by two eminences. 

 The upper bicuspids are larger than the lower. The roots are single, 

 but in the upper jaw they are slightly bifurcated at their extremities. 

 The permanent bicuspids make their appearance between the ninth and 

 the tenth years. 



The molar teeth, called respectively counting from before back- 

 ward the first, second and third molars, are the largest of all. Their 

 form is that of a cube, rounded laterally and provided with four or five 

 eminences on their opposed surfaces. The first molars are the largest. 

 They usually have three roots in the upper jaw and two in the lower, 

 although they sometimes have four or even five roots. The second 

 molars are but little smaller than the first and resemble them in nearly 

 every particular. The third molars, called the wisdom-teeth, are much 

 smaller than the others and are by no means so useful in mastication. 

 The first molars are the first of the permanent teeth, making their 

 appearance between the sixth and the seventh years. The second 

 molars appear between the twelfth and the thirteenth years ; and the 

 third molars, between the seventeenth and the twenty-first years, and 

 sometimes even much later. In some instances the third molars are 

 never developed. 



The upper jaw has ordinarily a somewhat longer and broader arch 

 than the lower; so that when the mouth is closed the teeth are not 

 brought into exact apposition, but the upper teeth overlap the lower 

 teeth both in front and laterally. The lower teeth are all somewhat 

 smaller than the corresponding teeth of the upper jaw and usually make 

 their appearance a little earlier. 



The superior maxillary bones are immovably articulated with the 

 other, bones of the head and do not usually take any active part in 

 mastication. Their inferior borders present fixed surfaces against 

 which the food is pressed by the action of the muscles that elevate 

 the lower jaw. 



