232 A MANUAL OF DENTAL ANATOMY. 



the individual teeth being more conspicuous. The whole 

 outer surface of the jaw near to its working edge is covered 

 by a sort of tesselated pavement, formed by the several 

 teeth which are pressed together into a mass, but they form 

 only the outer surface and the immediate edge, so that the 

 soft bone forms a part of the working surface, or would do 

 so but that, by its more speedy wear, it leaves the edge, 

 formed by dentine and enamel, always prominent and more 

 or less sharp. 



The structure and succession of these teeth have been care- 

 fully described by J. von Boas (Zeits. f. Wissen. Zool. xxxii.), 

 and the differences between the several genera pointed out. 

 He describes cementum as binding the denticles together 

 and forming a part of the working edge, but that which he 

 describes as cementum appears to me to be that tissue 

 which I have termed " bone of attachment." See page 208. 

 In a section of a jaw in my possession, which I believed 

 to have belonged to a Gymnodont fish but which bears a 

 remarkably close resemblance to that figured by von Boas 

 as being a jaw of Pseudoscarus, a very beautiful arrange- 

 ment serves to preserve the sharpness of the edge of the jaw. 

 The denticles are conical, and form a series of hollow 

 superimposed cones with the points upwards ; they consist 

 of dentine and enamel, and the point of the subjacent cone 

 fits closely up into the hollow of that above it, so closely 

 that in von Boas' specimen the dentine of the older tooth is 

 in great part absorbed to make way for the point of its 

 successor, so that the working denticle comes to be little 

 more than a hollow cone of enamel. This is not the case in 

 my specimen in which there is a quantity of dentine left 

 in each denticle. This vertical series of superimposed 

 sharp cones lie in the midst of the somewhat thin jaw bone, 

 fused together by cementum (1 bone of attachment), and 

 enclosed between the inner and outer plates of the jaw. 

 The bone being much softer than the denticle, wears 



