164 MICROSCOPIC ANATOMY OF THE TEETH 



as evidenced in the completed tissue, for considering that 

 these tubes are not an enamel product but are penetrating 

 dentinal tubes, and the evidence in favour of this view, 

 afforded by developing teeth, may now be considered. 



Although, as in all other mammalian enamels described, 

 calcification in the dentine in marsupials precedes that in 

 the enamel, yet when a small layer of calcified dentine only 

 is laid down, it can be seen that the area of enamel between 





FIG. 95. Developing tooth of Macropus cut without decalcification. 

 s. Stratum intermedium ; a. ameloblasts ; t. Tomes' processes ; e. enamel ; 

 d. calcified dentine ; o. odontogenic zone ; od. odonto blasts ; p. pulp. 

 (x75.) 



the ameloblasts and the dentine is very much wider than 

 that of the dentine (fig. 95), but this space is occupied by 

 the extended fibres of the Tomes' processes, and the calcifica- 

 tion within and between them is very incomplete. In this 

 section of an advanced germ of Macropus cut without 

 decalcification, and in which there is no disturbance of the 

 tissues, it is seen that a very much wider area of enamel 

 than of dentine is laid down ; in one part measured, the 

 enamel was found to be three times the width of the calcified 

 dentine. The stain employed (methylene blue) has uniformly 



