ART. 23. AN EXTINCT VARANID LIZARD GILMORE. 13 



The upper internal side of the dentary presents a beveled sur- 

 face, on which the expanded bases of the pleurodont teeth are at- 

 tached. This surface slopes downward from the outer alveolar 

 border of the jaw, and gradually increases in width from the poste- 

 rior end to the point where the bone is broken off. 



Sura7igvZar. — The surangular is the largest bone of the posterior 

 half of the ramus and forms the greater part of the external view 

 of this portion of the jaw (see A, fig. 12). Posteriorly it has a 

 pointed extremity which ends posterior to the cotylus of the jaw. 

 Ventrally the posterior half of this bone unites by a horizontal 

 suture with the underlying articular -f prearticular, the anterior half 

 with the smaller angular. The anterior end is truncated, this end 

 passing 5 mm. inside the posterior end of the dentary. On the ante- 

 rior, superior and upper lateral surfaces depressions of the bone 

 distinctly marks the depth of overlap of the dentary. On the supe- 

 rior anterior border a grooved surface marks the seat of the coronoid 

 bone which is detached. The posterior end of the surangular is 

 trasversely expanded and contributes slightly to the formation of 

 the anterior border of the cotylus for the articulation of the quad- 

 rate. On the inside of the jaw the surangular meets the prearticular 

 by a horizontal suture somewhat below the middle of the ramus and 

 continues forward to their contact with the overlying splenial. 



Angular. — The angular is a small pointed bone that underlies the 

 surangular externally and the forward extension of the prearticular 

 internally (see A, fig. 12). As in the living Monitor, a slender 

 pointed process continues forward, being intercalated between the 

 splenial and dentary, slightly in advance of the vertical surangular- 

 dentary suture. On the anterior internal side it is overlapped by a 

 posterior projection of the splenial. 



ArtiGular-\-2)reartiGular. — The so-called articular in the lizards is 

 considered by Williston^ to be the articular 4-prearticular complex. 

 There is no indication of a suture in this specimen to show which part 

 of this complex is articular and which is the prearticular portion. As 

 a matter of convenience in describing this part of the ramus, that part 

 of the complex lying in front of the cotylus will be arbitrarily con- 

 sidered the prearticular portion, and the posterior part, including 

 the cotylus, the articular portion. 



The articular + prearticular complex is an elongate bone that forms 

 the whole of the lower boundary of the ramus posterior to the angu- 

 lar and all of the extension of the jaw behind, including the cotylus 

 (see fig. 12). The prearticular portion extends forward beneath the 

 surangular to meet the angular, where it passes from a lateral view, 

 but internally it continues forward, the anterior end being inter- 

 calated between the splenial and dentary. Posteriorly it forms the 



*Journ. of GeoL, vol. 22, 1914, p. 411. 



