384 



ANATOMY OF VERTEBRATES. 



teeth rising from the mucuous membrane behind the rear rank of 

 the phalanx. 



This endless succession and decadence of the teeth, together 

 with the vast numbers in which they often coexist in the same 



26i 



Skull and jaws of Port Jackson Shark (Cestracion Phtlippii), showing the forms and arrangement of 



the teeth, v. 



Fish, illustrate the law of Vegetative or Irrelative Repetition, 1 as 

 it manifests itself on the first introduction of new organs in the 



o 



Animal Kingdom, under which light we must view the above- 

 described organised and calcified preparatory instruments of 

 digestion in the lowest class of the vertebrate series. 



o 



At the extreme limit of the class of Fishes, and connecting 

 that class with the Reptiles, stands the very remarkable genus, 

 the dental system of which is figured in cut 251. This consists 

 of two small, slender, conical, sharp-pointed, and slightly recurved 

 teeth, which project downward from the nasal bone, <?, and of 

 strong trenchant dental plates, anchylosed with the alveolar border 

 of the upper, , and lower, I, jaws, in each of which the plate 

 is divided at the middle, or symphysial line, so as to form two 

 distinct lateral teeth. The office of the two laniariform teeth is 

 to pierce and retain the nutritive substance or prey which is 



1 CCXLIX. 



