OUR FACE FROM FISH TO MAN 



end, after becoming ossified (after which it is 

 called the articular bone) serves for the main 

 articulation of the lower jaw with the primary 

 upper jaw; this arrangement persists from the 

 crossopt fishes up to the most advanced mammal- 

 like reptiles, which are the immediate predecessors 

 of the mammals. 



Each tooth of the above described fossil crossopt 

 fishes consists essentially of an enlarged cone with 

 an open pulp cavity, the sides of the cone being 

 very deeply infolded toward the base, so that in 

 cross-section the primary and secondary folds give 

 rise to the characteristic labyrinthodont pattern 

 (Fig. 18). The surface of the tooth is deeply 

 covered with enamel-like ganoine, which is folded 

 into the primary and secondary folds, and the 

 interior consists of dense, stratified bone or 

 dentine. The derm bone which bears the tooth 

 is strongly attached to it and is folded into its 

 sides along with the primary and secondary folds. 



This labyrinthodont mode of attachment of the 



teeth to the jaw bones is a far more primitive and 



important method than any of those commonly 



cited in textbooks on comparative dental anatomy, 



which usually describe only the either degenerate 



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