COGSWELL — ON THE HUMAN TEETH. 159 



the teeth of the pike, ox, and lion with those oi man give a laro^e 

 percentage in favor of the latter, the phosphate of lime being 

 greatly in advance of the other, 



Man. Lion. Pike. Ox. 



Dentine— 66.72 60.03 59.57 



Enamel— 89.82 83.33 63.98 81.86 



In man we find a difference in favor ^^ of the phosphate of lime 

 or enamel over the lion, while many teeth are composed only of 

 dentine and cement, like the great sperm whale, the cement taking the 

 place of enamel. The human tooth at first sight appears to be 

 composed only of dentine and enamel, but their crowns from the 

 gums are covered with enamel, while the roots are covered with a 

 cement or crusta petrosa. The internal structure of the teeth are 

 nourished 2coA supplied (of man) from the principal nerves run- 

 ning through the central portion of the teeth, thus we have a 

 longitudinal section of a cuspid tooth with various modifications, 

 tooth structure, nierve and its filanverds. The three different 

 substances so readily seen in the chart are these three disposed 

 according to ^h^ purposes required of them. 



First, we have the cement^im or crusta petrosa ; second, the den- 

 tine, (known as ivory in the tusk of the elephant) , and third, enamel. 



The first, cementum or crusta petrosa, corresponds in most 

 especial particulars with bone, possessing its characteristic /acwwoe 

 or small cavities, and being traversed by small medullary canals ; 

 this is the first covering of the young teeth, and covers the fang of 

 the tooth which enters the alveolar process of the jaw. 



The dentine or ivory consists of a firmer substance, in which 

 inorganic or mineral matter predominates less than the enamel. 

 This is traversed by a vast number of very fine tubulin (as seen on 

 the chart,) which commence at the pulp cavity and radiate toward 

 the surface. 



The size of these are immeasurably small, so much so that they 

 cannot receive blood, but no doubt like canaliculi of bone, imbibe 

 fluid from the pulp cavity, thus aiding in the nutrition of the 

 tooth. These tuhuli when deprived of enamel covering become 

 highly sensitive, and are the small telegraph wires, giving warn- 



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