44 A MANUAL OF DENTAL ANATOMY. 



of limited growth it terminates by a thin edge at the 

 neck of the tooth, where it is overlapped to some slight 

 extent by the cementum. When a thick coating of cemen- 

 tum exists over the whole crown, this lies outside the 

 enamel, the proper place of which is therefore between the 

 cementum and the dentine. 



The external surface of the enamel is finely striated, the 

 course of the strise being transverse to the long axis of the 

 crown ; in addition to this very fine striation, there may be 

 a few deeper and more pronounced grooves or pits, which 

 are pathological, and are marks of checks in development 

 more or less complete. The enamel of some animals is, to 

 all appearance, structureless ; such is the nature of the 

 little caps which, like spear points, surmount the teeth of 

 fishes of the eel tribe, cod tribe, or of the newt, and which 

 from their extreme brittleness are often lost in preparing 

 sections, so that their very existence has long been over- 

 looked. But the absence of structure, if such it really be, is 

 after all a mere question of degree ; in the commonest form 

 of enamel, such as that of the human teeth, there is a finely 

 fibrous structure, very apparent in imperfect teeth, but far 

 less so in well-formed ones, and the enamel of the eel is, in 

 the manner of its development, fibrous ; so that even though 

 we cannot distinguish its constituent fibres when it is com- 

 pleted, this is merely an indication that calcification has 

 progressed a little farther than in human teeth : if calcifica- 

 tion only goes far enough, all structure, if not destroyed, 

 will at all events be masked from sight. 



The structure of human enamel has been stated to be 

 fibrous ; that is to say, it has a cleavage in a definite direc- 

 tion, and is capable of being broken up into fibres or prisms, 

 which seem in transverse section to approximate more or 

 less closely to hexagonal forms brought about by their 

 mutual apposition. The general direction pursued by the 

 prisms is one from the dentine towards the surface ; this is, 



