THE DENTAL TISSUES. 47 



pattern found in the Manatee through that of the squirrel 

 and dormouse, and the porcupine, we see how a very definite 

 arrangement, at first simple, becomes modified into some- 

 thing a little more complex, till at last it reaches a degree 

 of complexity that looks like mere disorder. No one un- 

 familiar with the enamel of other rodents, looking at the 

 enamel of the porcupine, would be able to unravel the very- 

 indefinite looking chaos of prisms before him ; but had he 

 studied forms in some degree transitional he could not doubt 

 that the tortuous, curving course which he saw the prism 

 to be pursuing was nevertheless perfectly definite and precise, 

 and formed part of a regular pattern. 



In perfectly healthy human enamel the fibrillar arrange- 

 ment is not so very strongly marked ; the prisms are solid, 



FIG. 19 x . 



are apparently in absolute contact with one another, without 

 visible intervening substance. 



Bat Bodecker, basing his conclusions upon the examination 

 of thin sections, stained with chloride of gold, holds that 

 enamel is built up of columns of calcified substance, between 

 which minute spaces exist. These are filled by a material 



(*) Human enamel, from the masticating surface of a molar. The 

 figure is merely intended to show the general direction of the fibres. 



