26 



WATER REPTILES OF THE PAST AND PRESENT 



Fig. 9. — Mandible of Trimerorhachis, a, stegocephalian amphibian, ancestrally 

 related to the reptiles: A from within; B from without. The coronoid is composed 

 of three bones, the true coronoid (cor), the intercoronoid (icor), and the precoronoid 

 (j)c). The splenial is composed of two, the true splenial (i/i) and the postsplenial 

 {psp). The prearticular {pa) is broad, the dentary (d) is small; and the angular {an) 

 is only slightly visible on the inner side. 



Fig. 10. — Mandible of Labidosaurus, a cotylosaur reptile: A from within; B from 

 without. The coronoid {cor) is a single bone, but extends far forward. The splenial 

 (sp) is also a single bone, replacing the two of the amphibians. The prearticular {pa) 

 is narrower, and the angular {ang) appears broadly on the inner side. The dentary (d) 

 is much larger and the surangular {sa) is distinct. The articular {art) is small. 



