ENAMEL 97 



x 



Sir John Tomes (17 a) in 1849 first described the existence 

 of tubes in the enamel of marsupials, continuous with those 

 of the dentine. This fact was denied by Waldeyer and Hertz, " 

 but, as C. S. Tomes says, ' it is very difficult to understand 

 how any one looking at a section of a tooth of the Kangaroo 

 or Wallaby could have any doubts on this point '. J. Tomes, 

 moreover, showed that when marsupial enamel was de- 

 calcified the tubes were seen hanging out from the dentine 

 after the removal of the lime salts. 



In all marsupials, with the exception of the rodent-like 

 Wombat, these tubes can be seen ; but they are not by any 

 means developed to the same extent in the different families 

 of marsupials, where all degrees of penetration are seen 

 from the very complete one in Macropus to the scanty 

 development of the tubes in many Phalangers. In Macropus 

 the tubes not only enter in great abundance but traverse 

 nearly the whole width of the enamel, in many places 

 terminating just beneath the outer border. 



If a ground section of the enamel of Macropus be examined 

 under the microscope it is seen that the dentinal tubes pass 

 across the boundary at the amelo -dentinal junction, and 

 enter irregular dilatations or spaces, whence they are con- 

 tinued in more or less parallel lines into the enamel. A uni- 

 form bending of the tubes at an obtuse angle near the dentine 

 is a very frequent appearance in marsupials. 



The dilatations above referred to vary greatly in size 

 and contour, and in some places are altogether absent, 

 the tubes passing from the dentine directly into the enamel, 

 as seen in many parts in the teeth of the Hypsiprymninse. 

 When teeth of the Wallaby or Kangaroo are examined 

 which have been injected with alcoholic fuchsin from 

 the pulp cavity, the stain is seen to have passed uninter- 

 ruptedly across the boundary and along the whole length 

 of the tubes. The interprismatic substance also shows a 

 diffuse staining in places ; in fact, in many of these sections 

 the enamel appears to be more fully stained than the 

 dentine (figs. 52 and 53 A, B). 



This method of staining demonstrates very clearly the Termina- 

 continuity of the enamel tubes with the dentinal tubes. tlSesin 

 In some sections of the teeth of Bettongia (fig. 54), one of Bettongia. 



MDMMEEY JJ 



