PRIMARY AND SECONDARY CURVES. XXlll 



that the teeth are in the same condition as bone in this 

 respect. 



"The dentinal tubes, as before said, appear dark; 

 the lighter and apparently broader masses are the real 

 substance of the dentine. In this, and especially near 

 the layer closest to the enamel, dentinal cells are some- 

 times seen, which may probably be analogous to the 

 lacunae of bone. 



"If the dentinal curvatures are examined, it will be 

 seen that they are of two kinds. One set is in bold 

 and evident curves ; the other is not so evident, but it 

 exists, nevertheless, and a little patience and a high 

 magnifying power will demonstrate the fact that its 

 curves are upon the curves of the first set. The former 

 are called the primary, the latter the secondary curves 

 of the dentinal tubuli (in botanical description, a 

 biserrated leaf). From the tubuli minute bracelets 

 are given off on the sides, and toward the end the tubes 

 terminate, either in cells, by anastomosis, or by looping 

 back upon themselves. 



"The cement at first envelops the whole tooth, but 

 soon wears off the crown and as far down as the neck. 

 Compared with the dentine and enamel, it is very soft, 

 and more closely resembles bone ; in fact in some ani- 

 mals it is continuous with the bone of the jaw, thus 

 proving its identity. It contains lacunas and canalic- 

 uli, and, when there is a large mass of it, something 

 like Haversian canals. 



" There is a great analogy between tooth and bone. 

 In the cement there is absolute likeness, and in the 

 dentine, analogies too striking to be overlooked, viz., 

 the tubuli, analogous to the canaliculi, the intertubular 

 cells, analogous to the lacunae, and the intertubular 

 substance, analogous to the laminae of bone. In the 



