28 BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



depressions apparently indicates a strictly upward and downward movement of the 

 jaws. The articular forms more than one-half of the cotylus the anterior outer 

 portion being in the surangular. Posterior to the cotylus on the inner side, there 

 is an excejjtionally deep transverse notch (fig. 15., C). 



A higli thin transverse ridge separates this notch from the broad, oblique, 

 dorso-ventrally compressed posterior end of the articular which forms the most 

 posterior portion of the ramus. The articular is overlapped along its outer side by 

 the surangular, and on the ventral outer third by the prearticular. 



Prearticular (p. ar. and pr. ar.). — The prearticular is well showTi in figure 15. 

 It is a long curved clement that extends forward from the articular and forms the 

 lower posterior boundary of the ramus, externally it turns up and joins the inferior 

 border of the surangular as shown in A in figure 15. Unfortunately, on account of 

 the coalescnce of the suture with the articular the exact line of demarcation between 

 these two elements can not be determined. The forward prolongation at about the 

 center of the external mandibular foramen turns strongly upward terminating in a 

 pointed end at the top of the surangular. This part of the bone is relatively thin 

 transversely but considerably expanded antero-posteriorly as shown in figure 15, B. 

 It is almost identical in shape and position with the prearticular of Tirrannosaurvs 

 as figured by Osborn.' 



EXTERNAL OPENINGS IN THE SKULL. 



Viewed from the side, the openings in the skull of Antrodemus, begmning pos- 

 teriorly, are the lateral temporal fenestra, the orbito-infraorbital opening, the first 

 antiorbital fenestra, the second antiorbital fenestra and the anterior nares. I can find 

 no evidence of a third antiorbital fenestra in specimen No. 4734, U.S.N.M., such as 

 is present in Tijrannosaurus and which Osborn has observed^ in two skuUs of Antro- 

 demus in the collections of the Americair Museum of Natural History. Viewed dor- 

 saUy the supratemporal fossae on either side of the brain case are the only openings 

 of importance. No pineal opening present. 



Lateral temporal fenestra (lat. t. fen.). — The lateral temporal fenestra is a 

 vertically elongated opening, narrower above than below. This fenestra is bounded 

 above by the postemporal bar formed by the united processes of the squalnosal and 

 postorbital bones; anteriorly by the postorbital bar formed by the union of the 

 processes of the postorbital and jugal; ventrallj- by the quadratojugal and scjua- 

 mosal. The greatest vertical extent is 200 mm.; the greatest diameter antero- 

 posteriorly is SO mm. whereas the same measiu-ement in Ceratosaurus is 120 mm. 



Orhital opening (o.). — Like the temporal fenestra the orbital opening is verti- 

 cally elongated, widest antero-posteriorly at the middle, but narrowing at both top 

 and bottom. There is no partial separation of the infraorbital portion as in Tyranno- 

 saurus. Dorsally the upper boundary is formed by the postorbital-postfrontal 

 complex, frontal, and prefrontal; anteriorly by the prefrontal and jugal; ventrally 

 by the jugal, and posteriorly by the descending and ascending branches of the post- 

 orbital and jugal respectively. At the top a deep but narrow notch carries the 

 border in to the frontal. 



' Memoir Amer. Mus. Nat. Hist., new ser., vol. 1, pt. 1, 1912, p. 22, fig. 18. 

 2 Idem, p. 28, figs. 26, 27. 



