244 



EEPTILIA 



CLASS III 



known only from the Uppermost Cretaceous (Laramie Formation) of Mon- 

 tana, AVyoming, Coloi'ado, and Dakota. They are chiefly remarkable for 

 the armature of the huge skull, the strong, pointed horn -cores of which 

 resemble those of the Bovidae. Their rugose outer surface exhibits distinct 

 vascular impressions, and was doubtless once sheathed with horny tissue. 

 Internally they are hollow at the base, but become solid higher up. 



Tricerafops, Marsh {Polyonax, Jgathawmts, Cope), (Figs. 349, 350). Skull 

 over 1-5 m. long, exceeding in size that of any known land animal. Facial 



region compressed and pointed, hinder half 

 greatly expanded and hood-like. There is 

 a sharp cutting beak in front, a strong nasal 

 horn -core, a pair of large pointed horns 

 over the orbits, and a row of sharp pro- 

 jections around the margin of the posterior 

 hood. External nares very large, placed 

 between the nasals and rostral bone. Brain 

 cavity smaller in proportion to the skull 

 than in any other kno\vn reptile. Besides 

 the dentary, which develops a large coronoid 

 process, an articular, angular, surangular, 

 and splenial are distinguishable in the 

 lower jaw. Atlas and axis are fused with 

 the next cervical to support the head ; 

 ilSSTooU^Mafte^'laL^i^ ^^6 two lumbars and first four caudals 



fused Avith the sacrum, which has double 

 transverse processes, and the neural canal is not especially enlai^ged. Tail 

 of moderate length, chevron bones placed intervertebrally. The small per- 



FlG. 349. 



Triceratopsjerrat us, Marsh. Upper Cretaceous 

 Montana 

 worn max 



F 11^. 3u0. 

 rrkeratops prorsus, Marsli. Upper Cretaceous ; Montana. Restoration of skeleton, 1/70 ('ifter JIiu-sli). 



forated coracoid sometimes fused with the scapula in old individuals. Radius 

 and ulna short and stout, the latter with large olecranon process ; maiuis 

 with five hoofed digits. Ilium much elongated ; pubis massive, but with 

 slender post-pubic process. Ischium smaller and more elongated than the 

 pubis. Femur not much longer than the humerus, tibia and fibula short, the 

 latter very slender. Astragalus usually fused with distal end of tibia ; pes 



