CHAPTER IV 

 THE TEETH OF VERTEBRATES 



In this great sub-kingdom true teeth are the 

 rule and not the exception. They are enderonic 

 structures, because they are derived from the 

 deeper portions of the derm, or corium of the 

 integument, and possess a calcified tissue called 

 dentin. This is the main tissue of the teeth in 

 all Vertebrates, but in the higher forms the crown 

 is covered and protected by a calcified epithelial 

 tissue called enamel, and the root in the higher 

 forms is surrounded by a calcified osseous tissue 

 known as cementum. The teeth of the lower 

 Vertebrates, the Fishes and Reptiles, are com- 

 posed mainly of dentin, and to this the other 

 tissues, enamel and cementum, are added in the 

 higher forms. 



In position the teeth in the Vertebrates are 

 mostly confined to the oral cavity and to the bones 

 and cartilages of the head and face. In the 

 higher Vertebrates they are supported by the up- 

 per and lower jaws, — the maxillae and mandible 

 only. In the lower forms they may extend to the 

 thorax (or even to the oesophagus, as in some 



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