OSTEOLOGY OF CARNIVOROUS DINOSAURS. 



79 



The principal differences found by a comparison of the skulls of Ceratosaurus 

 and Antrodemus are contrasted in the two parallel columns below. 



ANTRODEMUS. 



1. None present. 



2. Lateral borders of nasals roughened and sharp. 



3. Skull, relatively wider, dorso-ventrally than 

 in Ceratosaurus. 



4. Quadrate relatively short. 



5. Premaxillary with 5 teeth. 



6. Upper dental series, 20-22 teeth. 



7. Second antiorbital fenestra present. 



8. Infratemporal fenestra relatively narrow at 

 bottom. 



9. External nares elongated. 



10. Nasals without pit. 



11. Nasals gradually narrowing. 



CERATOSAURUS. 



1. Prominent median horn-core on the nasals. 



2. Lateral borders of nasals smooth and rounded. 



3. Skull, relatively narrower, dorso-ventrally 

 than in Antrodemus. 



4. Quadrate, long. 



5. Premaxillary with 3 teeth. 



6. Upper dental series, 18 teeth. 



7. Second antiorbital fenestra appears to be 

 wanting. 



8. Infratemporal fenestra wide (anteroposteriorly) 

 at bottom. 



9. External nares oval. 



10. Pit on posterior median junction of nasals. 



11. Nasals, posterior to external nares swollen. 



Basioccipital (bo.). — The occipital condyle is hemispherical in general form, and 

 is inclined downwards, making an obtuse angle with the long axis of the skull. The. 

 basioccipital processes are short and stout, as compared with the narrower and more 

 ventrally elongated processes in Antrodemus. 



On account of the crushed condition of this region of the skull, the relationships 

 of the basioccipital with adjacent bones can not be accurately determined, though 

 I am inclined to believe they are somewhat different than in Antrodemus. 



Exoccipital (ex. oc). — The exoccipitals contribute to the upper articular surface 

 of the occipital condyle, meeting on the median line and entirely excluding that 

 element from the boundary of the foramen magnum. It can not be determined 

 whether these bones bridge over the foramen magnum, and thus exclude the supra- 

 occipital from its boundary as they do in Tyrannosaurus. Latterly they coalesce 

 with the paraoccipital processes. These processes are more widely expanded 

 vertically toward their outer ends than in Antrodemus, and with a heavier more 

 rugose outer extremity. In the skulls here compared the paraoccipital processes 

 of Ceratosaurus extend more obliquely backward, but this difference may be entirely 

 due to crushing, a point that can not be determined. Otherwise they are very 

 similar. 



Paraoccipital (p. oc). — The paraoccipital processes are present, but they are 

 so badly crushed that contrasting them with others of the Theropoda would be of 

 doubtful value. From what can be observed of their form and relationships they 

 appear to be very similar to those of Antrodemus, except that vertically their outer 

 ends are more widely expanded and more rugose than in that genus. 



Supraoccipital (so.). — On account of the crushed condition of this portion of 

 the occipital region and the coalescence of the sutures the boundaries of the supra- 

 occipital can not be determined. 



Alisplienoid (al. sp.). — The distorted condition of the alisphenoids and the 

 coalescence of the sutures in the Ceratosaurus skull render the comparison of this 

 element with those of other Theropod reptiles of little value. 



