OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



91 



What he [Lambe] regards as the angular is almost certainly a long process of the articular, such as 

 occurs in the lizards. If in Lambe's specimen there is really a suture between the articular and the 

 bone called by him the angular the latter is a distinct prearticular. Quite certainly in Ceratosaurus 

 the suture does not exist. Here the process reaches the foramen and a little below it. 



This more recent examination confirms Doctor Hay's conclusion regarding a 

 suture between the articular and prearticular, at this point. Osborn was unable 

 to detect it in the ramus of Tyrannosaurus studied by him although its probable 

 course is indicated by a dotted line. In the Antrodemus specimen No. 4734, U.S. 

 N.M., the prearticular is shown to extend to the angle of the jaw, underneath the 

 articular (see figure 15), and a close examination of the present specimen shows 

 a very similar condition. In advance of the posterior broken end of the left ramus 

 on the internal side is the broken end of the prearticular plainly shown as under- 

 lapping the articular. The rather indistinct suture can be traced forward for a 

 short distance where it appears to rise on the front of the articular, but its further 

 course can not be traced, except that in front of the articular it appears to unite 

 by a vertical suture with an inwardly directed . process from the surangular. 

 Ventrally the prearticular is underlapped by the angular. The anterior portion is 

 missing in this specimen, but in all probability it curved upward, the anterior end 

 being received between the coronoid and splenial as in Antrodemus and as indi- 

 cated in figure 55. 



The prearticular extends posteriorly nearly to the end of the articular, but 

 the surangular is slightly shorter and allows the articular to appear in a lateral 

 view. The posterior sutures between articular and surangular are very distinct, 

 but more anteriorly, especially those on the inner side, are coalesced and can no 

 longer be traced. Viewed from above the suture between the surangular and 

 articular runs diagonally across the outer fossa of the cotylus, but can not be 

 traced further than a deep pit between the inner fossa of the cotylus and the pre- 

 articular. All of the evidence appears to indicate the presence of the prearticular 

 as a distinct element as found in Tyrannosaurus and some other dinosaurs. Hay 

 considered this part of the lower jaw in Ceratosaurus as being a forward prolongation 

 of the articular, but I believe when a younger individual is known it will be found to 

 be a distinct element as in other Theropodou& dinosaurs. The deep pit mentioned 

 above is bounded on the inner side by a thin sheet of bone, but how much of it is 

 articular I am unable to determine because of the complete coalescence of the 

 sutures. The articular has a greatest transverse diameter of 73 mm; and an antero- 

 posterior diameter of 69 mm. 



Comparative measurements of Antrodemus and Ceratosaurus jaws. 



Greatest length 



Height of ramus below center of orbit 



Height of ramus center of dentary 



Length of dental series 



Antrode- 



Ceratosau- 



mus, 



rus. 



No. 4734, 



No. 4735, 



U.S.N. M. 



U.S.N. M. 



mm. 



mm. 



690 



650 



140 



119 



66 



64 



1 295 



280 



i No. 8335 U.S. Is. 



