ELEMENTS OF HIPPOLOGY. 



31 



Seventh: The mark, the dental star, and the shape 

 of the tables. 



All the details above enumerated are preliminary to the ex- 

 amination of the tables of the teeth and confirmatory of what is 

 to be learned from them. 



The structure of the incisors is the same for all: A central 

 cavity, the pulp cavity, containing the nerves, blood-vessels, 

 and secreting tissues, is contained in the axis of the tooth. Sur- 

 rounding this pulp cavity is dentine, a dense and ivory-like sub- 

 stance, forming the body of the tooth. This dentine in the per- 

 fect tooth 

 has a deep 

 hollow i n 

 i t s outer 

 end. Over 

 the surface 

 I of the tooth 

 and lining 

 the depres- 

 sion in its 

 outer end, 

 is enamel, 

 white, very 

 hard, and 

 of varying thickness. The depression in the tooth soon becomes 

 discolored frorn the debris of decomposing food lodging there. The 

 enamel that crowned the tooth at its appearance soon wears off, but 

 the enamel on the outside of the tooth and that lining its central 

 depression still shows in cross-section on the table of the tooth. 

 The blackened spot in the center of the tooth, with its surround- 

 ing ring of white enamel, is called the mark, and is present in 

 every permanent incisor for about three years after its appear- 

 ance. By this time, in the ordinary case, the grinding of the 

 teeth against each other has worn off that part of the tooth con- 



Figure 21. — Cross-Section of Center Incisor. 

 Drawn by Captain C. B. Hagadorn, 23d U. S. Infantry. 



