34 



MARINE EEPTILES OF THE OXFOED CLAY. 



inwards ; these seem to be functionally coronoid processes, the posterior one especially 

 having roughened surfaces for muscle-attachments. Behind these again the upper border 

 spreads out laterally and is deeply concave, the concavity being marked oif posteriorly by 

 a prominent tubercle (t), behind which is the thin upper edge of the expanded portion 

 which, as above described, bears the articular on its inner face. Ventrally the sur- 

 angular receives the upper border of the angular in front, while behind its outer 

 face is extensively overlapped by that bone. 



The angular {ang.) forms the lower border of the posterior part of the mandibular 

 ramus ; it consists of an elongated ventral portion, the upper edge of which, as just 

 mentioned, interlocks with the ventral border of the surangular ; below and internally 

 it is closely united with the splenial. Posteriorly it widens out and forms the postero- 

 inferior angle of the jaw ; in this region it extensively overlaps the surangular 



Text-fig. 22. 



sur.angj! B. 



a.s 



ang.f 



Eight articular bone of OpJithalmosaurus : A, inner surface ; B, outer surface. (E. 2180, |- nat. size.) 



ang.f., facet for the angular bone ; a.s., anterior surface ; cor.f., facet for the backward prolongation of the 

 coronoid bone ; i.s., inner surface ; p.s., posterior surface ; sur.ang.f., facet for the surangular bone. 



externally, while internally it is firmly united to two distinct facets on the lower edge 

 of the articular {g[.v.). On its inner side also its upper edge unites with the backward 

 prolongation of the coronoid. 



The coronoid {cor.) is situated entirely on the inner face of the ramus, and does not 

 project above it, the prominences on the surangular apparently replacing the true 

 coronoid process. In front the bone is deep and thin, and is wedged in between the 

 dentary on the inner, and the surangular on the outer side. Farther back it narrows 

 and is separated from the surangular by a deep fossa, which is closed behind by the 

 anterior end of the articular. Posteriorly the bone sends back a long process to the 

 hinder end of the jaw, wedged in between the lower side of the articular and the upper 

 border of the angular. 



The articular {art., text-figs. 20, 22) is a cartilage-bone quite diiferent in texture 



