316 



COMPARATIVE ANATOMY 



Spelerpes, Plethodon, Batrachoseps, Fig. 230) ; in the larvae of Sala- 

 manders and in Proteus the splenial of the lower jaw is also 

 toothed. Horny teeth and horny jaws are present in larval 

 Anura (except Xenopus), and similar structures occur in Siren 

 lacertina. Teeth are altogether absent in the Bufonidae and in 

 Pipa. 



The teeth of certain of the Stegocephali (Labyrinthodonta) 

 were extremely complicated, the enamel forming numerous 

 corrugated folds extending from the periphery towards the 

 centre. 



Reptiles and Birds. Corresponding with the greater firm- 

 ness of the skull in Reptiles, the teeth are usually strongly 



ZK 



RF 



zs 



B 



Fi<;. 231, A TOOTH OF FROG, and B OF Salnmiilra atra. 



M, maxilla ; PH, pulp-cavity ; RF, circular furrow ; S, apex, covered with 

 enamel ; ZK, crown ; ZS, base. 



developed, and may be more highly differentiated than in Amphi- 

 bians. They are either situated upon a ledge on the inner 

 side of the lower jaw, with which their bases become fused 

 (pleurodont dentition most Lacertilia) ; or they lie on the free 

 upper border of the jaw (acrodont dentition Chameleon); or 

 finally, as in Crocodiles and numerous fossil Reptiles, they are 

 lodged in alveoli (thecodont dentition) (Fig. 232). Both upper 

 and lower jaws, and occasionally the palatine and pterygoid also, 

 are toothed (Lizards and Snakes) ; and in Hatteria, vomerine 

 teeth may also be present. The teeth are usually conical, more or 

 less pointed (Fig. 232, B), and often long and recurved, for seizing 

 the prey (e.g. Snakes) : in Lizards the apex may be double, and 

 in many Reptiles (e.g. Uromastix spinipes, Agamae, and numerous 



