DIGESTION. THE TEETH. 59 



one or more points, is called the root of the tooth. Finally, we 

 often remark between the crown and the root, a slight shrinking, 

 called the neck of the tooth. 



30. The teeth are composed of an internal substance called 

 ivory, and a sort of extremely hard stony varnish, which covers 

 the surface, and is called enamel. 



31. The crown of the tooth only is covered with enamel. The 

 root has it not. 



32. The teeth are formed in the interior of Fig. 16. 

 the jaws, and within little membranous pouches 



called dental capsules, which are inclosed with- 

 in the substance of the bone, and which present 

 in their interior a fleshy bud, or granule, from c 

 the surface of which exudes the stony mat- 

 ter of which the tooth is composed, (fty. 16.) 



33. This stony matter is the ivory ; it moulds 

 itself upon the bud, and takes its form ; just in 

 proportion as new quantities of ivory are 



deposited upon that already formed, the tooth enlarges, as well as 

 the species of case which it forms around the bud, which shrinks 

 away until finally the little organ, being too much compressed, 

 disappears ; the tooth then ceases to grow. 



34. In proportion as the tooth is formed, as we have just said, 

 it rises in the alveolus, passes through the gum, and shows itself 

 without. 



35. The enamel is formed at the superior portion of the dental 

 capsule, and is applied upon the tooth just to the extent it traverses 

 that part of the capsule ; it is for this reason that the root, which 

 lemains at the bottom of the alveolus is never covered by it. 



36. The teeth which are formed in the earliest period of life, 

 are destined soon to fall, and to give place to other teeth, stronger 



Explanation of Fig. 16. One of the dental capsules opened to show the 

 fleshy tubercle or granule which is in it, 6, the tubercle upon which the 

 tooth in a manner moulds itself; v. blood vessels and nerves which enlei 

 into this little secreting organ, d. part of a tooth which has just begun to 

 form, c. capsule. 



30. What is the composition of teeth ? What is ivory ? What is enamel 7 



31. Have all parts of the tooth a covering of enamel ? 



32. How are the teeth formed ? What are the dental capsules? What 

 do they contain ? What office does this granule fulfil? 



33. How do teeth prow or increase in size ? Do teeth always continue to 

 grow ? Does the bud or granule always exist in the tooth ? 



34. How does the tooth rise in the alveolus ? 



35. W r here is the enamel formed ? How is it applied to the tooth ? Why 

 IP there no enamel on the roots of the teeth ? 



36. Dp the teeth of infancy remain through life ? 



G 



