LABROIDS. Ill 



with .the beautiful illustration of the best mechanical principles by 

 which enormous pressure can be sustained and transferred to par- 

 ticular points. 



To crush the hard shells of marine testacea and comminute them 

 for deglutition requires strong teeth and the requisite power to work 

 them ; and of a dentition adequate to such purposes we have frequent 

 examples in the class of fishes. The jaws of the wolf-fish, figured 

 in plate 60, are peculiarly well provided with instruments for this opera- 

 tion. But in the wrasse, the waste of the molar teeth consequent on 

 the rude attrition to which they are subject, is repaired by the develop- 

 ment of new teeth directly beneath those in use, whilst in the wolf- 

 fish the new teeth are formed by the side of the old. Here, then, a 

 new difficulty was to be obviated ; had the crushing tooth rested by 

 the whole of its basis upon the alveolus, as in the wolf-fish (see the 

 section of the jaw of that species figured in PI. 60, fig, 2), the sup- 

 porting plate, gradually undermined by the growth of the new tooth, 

 would have given way, and been forced upon the subjacent delicate 

 and highly vascular matrix with the half-formed tooth : this, there- 

 fore, must have either sustained the irritation and injury of the 

 undue pressure, or the important functions of the pharyngeal grinders 

 must have been temporarily suspended, until the undermined tooth had 

 been shed, and its successor sufficiently solidified and adequately 

 fixed. 



To obviate this evil, the centre of the pulp of the pharyngeal 

 molar remains uncalcified long after the tooth has taken its place, 

 and the circumference only of the base of the tooth rests upon the 

 raised margin of the alveolus. The part of the tooth which sustains 

 and transmits the pressure is strengthened by the development of a 

 strong convex ridge projecting from its inner surface into the pulp- 

 cavity ; and the calcigerous tubes of this ridge, while simply following 

 the ordinary course of development, acquire a direction the best 

 adapted for diffusing the pressure equally to every point, by radiating 

 from the plane of resistance. The pressure received by the border of 

 the alveolus is transferred to the walls which divide the vaulted 

 cavities containing the germs of the new teeth. The roof of these 

 cavities, which forms at the same time the floor of the alveolus above, 



