52 MICROSCOPIC ANATOMY OF THE TEETH 



have an arched appearance, being rounded on one aspect 

 and more or less concave on the opposite side (fig. 24), 

 as will be more fully explained later. Prisms of hexagonal 

 form are not very frequently met with in human teeth, and 

 Leon Williams describes them as usually oval or rounded 

 (see fig. 16). In marsupial enamel they appear, however, 

 to be more constantly of an hexagonal form. 



Bodeker holds that there is a living protoplasmic network 

 between the enamel columns continuous with the contents 



FIG. 16. Transverse section of enamel showing oval and rounded 

 sections of prisms. ( x800.) 



of the dentinal tubes, but such a view is at variance with 

 all our knowledge of the structure and composition of enamel, 

 and is certainly due to a misinterpretation of appearances. 



The course of the enamel prisms is more regular in some 

 orders of Mammalia ; in the Manatee they are in many places 

 arranged in straight parallel lines, and the Rodents especially 

 show curiously regular patterns which will be further 

 explained when treating of rodent enamel. 



As the area of the enamel is much greater at the outer 

 surface than at the dentine junction it is supposed that there 

 must be supplemental prisms interposed, but these, owing 

 to the complicated pattern of the enamel, are difficult to 



