MASTICATION. 191 



blood-vessels and nervous filaments, held together by longitudinal fibres of 

 connective tissue. This is the only portion of the tooth endowed with sensi- 

 bility. The blood-vessels and nerves penetrate by a little orifice at the ex- 

 tremity of each root. 



The dentine and enamel of the teeth must be regarded as perfected struct- 

 ures ; for when the second, or permanent teeth are lost, they are never re- 

 produced, and when these parts are invaded by wear or by decay, they are 

 not restored. 



The thirty-two permanent teeth are classified as follows : 



1. Eight incisors, four in each jaw, called the central and lateral incisors. 



2. Four canines, or cuspidati, two in each jaw, just back of the incisors. 

 The upper canines are sometimes called the eye-teeth, and the lower canines, 

 the stomach-teeth. 



3. Eight bicuspid the small, or false molars just back of the canines ; 

 four in each jaw. 



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, which 

 is sometimes perfectly straight but is generally more or less rounded. Each 

 incisor has a single root. The special use of the incisor teeth is to divide the 

 food as it is taken into the mouth. The permanent incisors make their ap- 

 pearance between the seventh and the eighth years. 



The canines are more conical and pointed ^han the incisors, and have 

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

 single. They are used, with the incisors, in dividing the food. The perma- 

 nent canines make their appearance between the eleventh and the twelfth 

 years. 



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

 posed 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. They are used, 

 with the true molars, in triturating the food. The permanent bicuspids 

 make their appearance between the ninth and the tenth years. 



The molar teeth, called respectively counting from before backward 

 the first, second and third molars, are the largest of all and are, par excel- 

 lence, the teeth used in mastication. 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 have generally 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 resem- 

 ble them in nearly every particular. The third molars, called frequently the 

 wisdom-teeth, are much smaller than the others and are by no means so use- 

 ful in mastication. The first molars are the first of the permanent teeth, 

 making their appearance between the sixth and the seventh years. The sec- 

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



