30 



100. The left superior pharyngeal bone of a large fish of the genus Cossyphus. 



It is paved with rounded or flattened molars of different sizes. Some of these 

 have been shed, and the germs of their successors are exposed in the closed 

 alveoli, which are immediately above the teeth that are shed. Hunterian. 



101. A right superior pharyngeal bone of a large fish of the genus Cossyphm; 

 it is vertically bisected, showing the mode of attachment of the teeth in use, 

 and the cavities of reserve with the germs of the successional teeth beneath 

 them. 



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 pres- 

 sure 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 subjacent 

 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, being thus relieved from the superin- 

 cumbent weight, freely yields to the absorbent process consequent on the growth of the new 

 tooth ; and before the latter becomes subjected to any pressure from above, its formation has 

 been sufficiently perfected to enable it to sustain that pressure without injury. The lateral 

 walls of the cavities containing the reserve teeth, to which the pressure is transferred from 

 the margins of the sockets of those in use, consist of a much denser osseous tissue than the 

 other parts of the pharyngeal bone. 



Hunterian. 



102. An inferior pharyngeal bone of a Labroid fish, longitudinally bisected, show- 

 ing the cavities of reserve of the successional teeth. Hunterian. 



103. The upper and lower pharyngeal bones and teeth of a small Labroid fish, 



called the ' Red-mouthed Grunt ' on the original label. Hunterian. 



104. The basibranchials and hypobranchials of the third and fourth gill-arches, and 



the coalesced basibranchials of the fifth arch, which form the basis of support 

 for the inferior pharyngeal teeth, of a small Wrasse or Labroid fish. 



Hunterian. 



