26 WATER REPTILES OF THE PAST AND PRESENT 



an. 



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 

 (pc). The splenial is composed of two, the true splenial (sp) 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 otLabidosaurus, 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. 



