96 MICROSCOPIC ANATOMY OF THE TEETH 



geal teeth where vascular loops encroaching on the enamel 

 are also visible. 



Fig. 50 shows one of the teeth in use at the margin of 

 the maxilla, which has undergone very extensive absorption 

 of the dentine, and also of the enamel where the successional 

 denticles are advancing. Fig. 49 also shows the excavation 

 of the denticles farther back in the jaw, the dentine at a, as 

 in fig. 50, having almost entirely disappeared. Fig. 51 



FIG. 51. Section of upper jaw of Pseudoscarus showing 

 arrangement of denticles in the bone. ( x 10.) 



shows under lower magnification the superimposed teeth of 

 the maxillary bone of Pseudoscarus. 



The Tubular Enamel of Marsupials 



The tubes in marsupial enamel are entirely connected 

 with the dentinal tubes, and there is no penetration of the 

 enamel from without as in many fish. 



The determination of the exact nature and significance 

 of this tubular condition is of the greatest importance in 

 the study of the development of marsupial enamel and of 

 mammalian enamel generally, and will be considered more 

 fully in the chapter on ' Development of the Enamel '. 



