680 



DR. 11. UROOM ON TllK STRUCXURK 01;" TilE SKULL 



We also know fully the structure in some of the Pelycosaurs. 

 In the early reptiles more related to the primitive Diapsitlans 

 — the Ichthyosaurs and the Plesiosaurs— the structure is also 

 satisfactorily known. 



Quite clearly the affinities of the Titanosuchian jaw are with 

 those of the Anomodonts and Gorgonopsians ; and though in 

 each of those three groups the jaws have some quite charac- 

 teristic features, the jaw structure shows that there is a close 

 genetic relationship between the three. 



If the Titanosuchits jaw be compared with that of a Gorgon- 

 opsian, it will be seen that the two are fundamentally similar. 



Text-lis>ure 13. 



A. Transverse section of the jaw of Dicynodon audreivsi Broom near the middle 



of the jaw, I'or comparison with suction CC of the jaw of Titaiiosuvhus 

 clootei Uroom. The curious overlapping of the prearticular hj' the splcnial 

 is seen. 



B. A similar section a little further hack from another jaw of Bicynodon spec. 



C. Section through the hack of the jaw of a young Gorgonopsian, showing the 



splitting of the angular. Compare with section E E of jaw of Titanosuchtis 

 cloetei Broom. 



The Gorgonopsian diflers in having a much larger coronoid bone, 

 which serves as a splint to bind the back part of the dentary and 

 the front part of the prearticular. The dentary has a well- 

 developed coronoid process which is lacking in Titanosuchus. 

 The articular is much smaller in the Gorgonopsian, in keeping 

 with the very small size of the quadrate. The Gorgonopsian 

 angular shows the same sort of splitting that is seen in Titano- 

 suchus ; but in the Gorgonopsian the outer plate is much less 

 fully developed. 



The Anomodont jaw also shows marked affinities with that of 

 Titanosuchus, but these are to some extent obscured by the 

 remarkable specializations. There have been one or two points 



