THE ATTACHMENT OF TEETH. 205 



thickened edge is received upon a little buttress of bone, 

 and it occupies a much higher level than the opposite thin 

 edge to which the hinge is attached, so that the tooth cannot 

 possibly be bent outwards without actual rupture of the 

 ligament. 



And what is not a little remarkable is, that whilst the 

 Hake, the most predatory of all the Gadidce, is possessed of 

 these very perfectly hinged teeth, other members of the 

 family have teeth moveable in a less degree, whilst others 

 again have teeth rigidly fixed. So that within the limits of 

 a single family we have several steps in a gradual progres- 

 sion towards a very highly specialised organ. 



In the hinged teeth already alluded to the purpose served 

 by their mobility seems to be the catching of active fish, and 

 the elasticity resides solely in the hinges ; but the common 

 Pike possesses many hinged teeth which seem to be con- 

 cerned in the swallowing of the prey after it has been caught, 

 and there is no elasticity in the hinges, the resilience of the 

 teeth being provided for in another way. 



The teeth which surround the margins of the jaws are 

 anchylosed, and they are more or less solidly filled up in 

 their interior with a development of osteodentine, which, by 

 becoming continuous with the subjacent bone, cements them 

 upon it. The manner of development of this is by rods of 

 calcifying material shooting down through the central pulp 

 (see page 165) j in the hinged teeth also these trabeculse shoot 

 down, and become continuous with the subjacent bone, only 

 instead of rigidly ossifying they remain soft and elastic, so 

 that the tooth is like an extinguisher fastened down by a 

 large number of elastic strings attached to different points 

 on its interior, and hinged at one side. 



The elasticity is very perfect, so that the teeth depressed 

 and suddenly released return with an audible snap, but it 

 resides solely in these strings, for if these be divided by 

 carefully slipping a cataract needle under the tooth without 



