loS Sub/lance of tie Teeth. [Book IX. 



figned for the grinding of the food. The anterior 

 molares are fmaller and lefs uneven on the corona than 

 the pofterior; the ftrongeft being placed neareft the 

 articulation of the jaw bone, becaufe there we can 

 exert the greateft force. The roots of the molares are 

 long and pointed ; each tooth has two, three, four, and 

 fometimes, though very rarely, five roots. The roots 

 fometimes ftand feparate, fometimes are concreted 

 together; fometimes they are (trait, fometimes crooked. 



The fubftance of the teeth is compact. The corona 

 is covered with a curious fubftance, called the enamel. 

 This is thin, white, fhining, and, being the hardeft 

 and moil compact fubftance in the body, is admirably 

 adapted to the purpofes of maftication. 



It 13 fcarcely neceflary to remark, that in eating we 

 only move the lower jaw, and that the upper is on all 

 occafions fixed and immoveable, 



In the infant ftate, two fets of teeth are already ob- 

 fcrvable in the jaw-bones. In the cutting of the teeth, 

 the incifores firft make their appearance, in general 

 about the eighth month; and afterwards, at about two 

 years of age, two molares and the dog-tooth. The firft 

 fet of teeth when complete is bun twenty in number, 

 viz. eight incifores, eight molares, and four eanini. 

 In the fecond fet are added twelve molares, viz. three 

 on each fide in each jaw, making the complete fet in 

 the adult thirty- two. To make room for this addition, 

 the jaws undergo a gradual elongation. Hence the 

 face is fo much lengthened from eight to eighteen years 

 of age. About the feventh year the fecond fet begins 

 to fupply the place of the firft, which by this time be- 

 come loofe, by the wafte of the lockets and the growth 

 of the teeth below. 



If we extend our views to the lower animals, we 

 ihall find no part of the body more various among 



different 



