FORMATION OF THE TISSUES TEETH. 



489 



unequal i.vear of these substances,' the Enamel being the hardest, and the 

 Cementum the softest, occasions this surface to be always kept rough. 



634. The Enamel is composed of solid prisms or fibres, about l-5600th of 

 an inch in diameter, arranged side by side, and closely adherent to each other ; 



[Fig. 121. 



[Fig. 122. 



A vertical section of an imperfectly developed Incisor, 

 taken from the follicle in which it was enclosed; this sec- 

 tion is meant to show the position of the enamel fibres, and 

 also that a part of the appearances which are seen in this 

 substance under a less magnifying power, originate in 

 parallel curvatures of the fibres; 1, 1, the enamel ; 2, 2, the 

 dental bone, or ivory ; 3, 3, the minute indentations and 

 points on the surface of the ivory, on which the enamel 

 fibres rest; 4, 4, brown parallel fibres; 5, parallel flexions 

 of the fibres of the dental bone in these stripes.] 



A portion of the surface of the Enamel 

 on which the hexagonal terminations of 

 the fibres are shown highly magnified; 

 1, 2, 3, are more strongly marked dark 

 crooked crevices, running between the 

 rows of the hexagonal fibres.] 



their length corresponds with the thickness of the layer which they form ; and 

 the two surfaces of this layer present the ends of the prisms, which are usually 

 more or less regularly hexagonal. The course of these prisms is more or less 

 wavy ; but their curves are for the most part parallel to each other. In the 



[Fig. 123. 



[Fig. 124. 



The Fibres of the Enamel viewed sideways 

 under a magnifying power of 350 times ; 1, 1, 

 the enamel fibres; 2, 2, the transverse stripes 

 upon them.] 



A small portion of fig. 120 covered with turpentine 

 varnish, viewed under a magnifying power of 350 

 times; 1, 2, 3, are the tubes containing a powdery, 

 lumpy substance. They are regular, and closely un- 

 dulating ; but the branches do not appear, because they 

 are penetrated by the varnish.] 



perfect state, the Enamel contains but an extremely minute quantity of animal 

 matter; but if a young tooth be examined, it is found that, after the calcareous 

 matter of the tooth has been dissolved away by an acid, there remains a set of 



