866 



TEETH. 



tissue.* Fig. 545. illustrates this structure in 

 a longitudinal section of a tooth of a shark of 



Fig. 515. 



Fig. 517. 



Section of tooth of Lamna, magnified. 

 ( Owen's Odontograpluj. ) 



the genus Lamna : v is the vaso-dentine ; d 

 the hard dentine; the earthy constituent so 



Pis. 546. 



Section of tooth of Dagnng ( Tlallcore}, magnified. 

 * Odontography, pp. 17. 37. 



Section of tooth of Cachalot (Physeter). 



predominates that the tissue 

 takes a polish like enamel, for 

 which it has commonly been 

 mistaken in the teeth of fishes : 

 I have called it " vitro-den- 

 tine." 



The molars of the Dugong 

 are examples of teeth com- 

 posed of dentine and cement, 

 the latter tissue forming a 

 thick external layer. Fig. 

 546. A. is a transverse section 

 of the crown of the second 

 molar, natural size; and B. 

 a magnified view of a por- 

 tion of the section ; d the 

 dentine, remarkable for the 

 number of minute calcigerous 

 cells at its periphery ; and c 

 the cement. 



In the great teeth of the 

 lower jaw of the Cachalot, 

 the pulp-cavity of the growing 

 tooth becomes filled up by 

 osteo-dentine, the result of a modified calci- 

 fication of the dentinal pulp ; and the full- 

 grown tooth presents three tissues, as shown 



