66 MICROSCOPIC ANATOMY OF THE TEETH 



of the amelo blasts, which are prolonged into the enamel 

 and constitute the longitudinal system of organic fibres 

 which form the foundation of enamel. 



In studying the wing processes the author also made use 

 of marsupial enamel, which in many respects appears to 

 give us the key to the mode of formation of higher mamma- 

 lian enamels ; it is less perfectly calcified, at all events in 

 early stages, and the structure is more easily made out 

 than in a tissue which is very rapidly calcified and in which 

 the early stages of development are soon obscured by the 

 densely deposited lime salts. Teased preparations of the 

 forming enamel of Macropus rufus were examined. The 

 wing processes were very much more evident than in any 

 other enamel investigated ; they have a more feathery 

 appearance and often pass right across groups of prisms, 

 and appear to show a transition into membrane-like expan- 

 sions (Plate III , figs. 1 2 and 13). This would appear to indicate 

 that wing processes and these calcified membranes are one 

 and the same thing, and, as before stated, the wing processes 

 and transverse fibres of the membrane-like expansions are 

 seen to pass almost at right angles to the columns of prisms 

 and their pointed needle-like fractured terminations. The 

 author was, however, unable to detect in marsupial enamel, 

 either in early or completed stages, the curious interlocking 

 of the prisms described by Smreker in human enamel. 

 The prisms in all marsupials examined show the usual 

 polygonal forms in transverse section, and no longitudinal 

 grooving could be detected in teased preparations. 



It may be that the interlocked prisms indicate a more 

 highly developed and specialized structure of the enamel. 

 Inter- The intercolumnar bridges are somewhat difficult to 



Detect i n human enamel ; they are shown in fig. 14 and in 

 several of Leon Williams's photographs. In the Elephant 

 they can be seen with great distinctness both in longitudinal 

 and transverse sections (11 a). A study of the microscopic 

 anatomy of the enamel of the Elephant which curiously seems 

 to have escaped the attention of histologists, convinced the 

 author that this remarkable form and arrangement of the 

 prisms is an actual fact and not a false appearance due 

 to the prisms being viewed obliquely, for in the Elephant 



