230 A MANUAL OF DENTAL ANATOMY. 



row ; the vomer is also armed with a double row of very 

 much larger and shorter teeth ; the lower jaw, with the 

 exception of its anterior part, is occupied by teeth of similar 

 character. 



All the teeth of the Wolf-fish are anchylosed slightly to 

 the bone, a definite process from which forms a sort of short 

 pedestal for each tooth. The jaws are worked by muscles 

 of great power, and it seldom happens that a specimen is 

 examined in which some of the teeth are not broken. It 

 feeds upon shell fish, the hard coverings of which are 

 crushed by the blunter teeth, while the pointed front teeth 

 apparently serve to tear the shell fish from the rocks to 

 which they are commonly attached. 



In the group of fish known as " Gymnodonts " (naked 

 toothed), the teeth and the margins of the dentigerous bones 

 form a sort of beak, which is not covered by the lips. The 

 example here figured consists of the upper and lower jaws of 

 the Diodon, so called because it appears to casual observators 

 to have but two teeth. A kindred fish in which the division 

 of each jaw in the middle line is conspicuous, is similarly 

 called Tetrodon. The jaw consists of teeth and bone very 

 intimately fused together; the broad rounded mass (c. in 

 the figure), which lies just inside the margin of the jaws, is 

 made up of a number of horizontal plates of dentine, the 

 edges of which crop out upon its posterior surface ; and 

 these are united to one another by the calcification of the 

 last remains of the pulp of each plate into a sort of osteo- 

 dentine, the different hardness of the two tissues keeping 

 the surface constantly rough, as the plates become worn away. 

 The whole margin of the jaw is similarly built up of smaller 

 horizontally disposed denticles, or plates of dentine, which 

 are, as they wear down, replaced by the development of 

 fresh plates, which are added from beneath, where they are 

 developed in cavities situated low down in the substance of 

 the bone. 



