DENTITION OF LOWER VERTEBRATES 37 



limited degree and hence once again our generalization falls 

 short of completeness. Many Mammals, the domestic Cat 

 among them, use their teeth only for seizing and dividing their 

 prey not for masticating it. Teeth are then in the first place 

 prehensile organs and only later become modified for dividing, 

 crushing or masticating food. For the mere seizing and hold- 

 ing of prey the conical teeth seen in many fish are perfectly 

 satisfactory and it is with such simple forms that our study 

 must commence. 



The numerous modifications of form, structure and attach- 

 ment of teeth as exemplified by Fishes have no immediate con- 

 cern for us since our object is the investigation of the mam- 

 malian dentition and we may therefore pass on at once to con- 

 sider teeth in higher forms. 



On an evolutionary plane higher than that of the Fishes Ave 

 find the now specialized and aberrant group Amphibia which 

 includes the Frogs, Toads, Newts and Salamanders. Upon ex- 

 amination the upper jaw of the Frog shows a row of small 

 conical teeth firmly ankylosed to the underlying bone and pro- 

 jecting but little from the surface of the soft tissues lining the 

 mouth Avhile the lower jaw is edentulous. There are other teeth 

 upon the palate, the so-called vomerine teeth, also simple and 

 small but Ave shall not stay to consider them. The Frog is not 

 limited to one set of teeth alone; successional teeth originally 

 developed at the inner aspect of the older teeth eventually 

 undermine the bony pedestal of the last mentioned and com- 

 plete their development in what Avas originally the pulp cavity 

 of their predecessors, ultimately being fused Avith the bony tis- 

 sue precisely as are the teeth on the jaws. 



Higher in the scale than Amphibians are the Reptiles which 

 comprise Lizards, Snakes, Turtles and Alligators. All of these 

 have become specialized although the Lizards perhaps less 

 than the rest. But all modern Reptiles are far removed from 

 the main evolutionary track Avhich Ave intend to folloAv. Never- 

 theless among them are to be found many interesting modifica- 



