26 



WATER REPTILES OF THE PAST AND PRESENT 



Fig. q. — Mandible of Triwcrorluichis, a stcgoccphalian ami)hibian, ancestrally 

 related to the reptiles: .1 from within; B from without. The coronoid is composed 

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

 ipc). The splenial is composed of two, the true splenial {sp) and the postsplenial 

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

 is only slightly visible on the inner side. 



Fk;. lo. — MandibleofZ,a6/</o5aKrH5, a cotylosaur reptile: A from within; /} 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 {aiiji) appears broadly on the inner side. The dentary {d) 

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



