80 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



Basisphenoid (b. s.). — The basipterygoid processes are more strongly developed 

 than in Antrodemus. The cavity on the median ventral side of the basisphenoid, 

 which probably leads up to the foramen for the median Eustachian canal is not so 

 large as in the latter genus, and on account of being filled with matrix its upward 

 extent can not be determined. 



Parasphenoid (p. sp.). — The parasphenoid in Ceratosaurus was first recognized 

 by Hay, 1 and as shown in figure 54, (21), is a vertical plate of bone with a pointed 

 anterior extremity that extends forward from the front of the basisphenoid. Crush- 

 ing and adhering matrix render its relationship with the orbitosphenoids obscure. 

 Above, it supports what appears from its position to be the ethmoid. 



£ r°s 



-p?nx 



cm 



Fig. 53.— Skull of Ceratosaurus nasicornis Marsh. Side view. No. 4735, U.S.N.M. \ nat. size, an, angular; ar, 

 articular; d, dentart; /' first antiorbital fenestra; ;', jugal; la, lachrymal; lat.t.fen, lateral temporal 

 fenestra; n, nasal; n.h, nasal horn core; o, orbit; p, parietal; p.ar, prearticular; p.f, prefrontal; pmx, 

 premaxillary; po.f, postfrontal+postorbital; p.oc, paraoccipital; pt, pterygoid; g, quadrate; gj, quadrato- 

 jugal; sa, surangular; sg, squamosal. 



Parietal (p.). — The sutures defining the boundaries of the parietals are largely 

 obliterated. Between the supratemporal fossae, the parietal surfaces appear more 

 rounded transversely than in Antrodemus. The thin plate-like transverse exten- 

 sions of the parietal has been represented by Marsh in his figure of the superior 

 view of the skull of Ceratosaurus nasicornis as having the dorsal border continuing 

 outward to unite strongly with the postorbital and the squamosal bones. In this 

 he was in error, for with the articulated skull of Antrodemus as a guide it is plainly 

 evident the relations of these bones are very similar. There is a deep notch between 

 the parietal and squamosal at the back of the supratemporal fossa, as in both 

 Antrodemus and Tyrannosaurus. At the bottom of this notch, as shown in figure 1, 

 plate 18, the parietal has a weak union with the squamosal. Moreover the articu- 



i Proc. U. S. Nat. Mus., vol. 35, 1908, p. 360, figs. 1 and 2 (21). 



