CRETACEOUS VERTEBRATE FOSSILS. 513 



The skull of Triceratops, the best-known genus of the family, has 

 many remarkable features. First of all, its size, in the largest individuals, 

 exceeds that <>t' any land animal hitherto discovered, living or extinct, and 

 is surpassed only by that of some of the Cetaceans. 



Another striking feature of the skull is its armature. This consisted of 

 a sharp, cutting beak in front, a strong horn on the nose. ;i pair of very 

 lame, pointed horns on tin- top of the head, and a row of sharp projections 

 around the margin of the posterior crest. All these had a horny covering 

 of great strengthand power. Foroffense and defense they formed together 



an armor for the head as complete as any known. This armature domi- 

 nated the skull, and, in a greal measure, determined its form and structure. 

 In some species the armature extended over portions of the body. 



The skull itself is wedge-shaped in form, especially when seen from 

 above.' The facial portion is very narrow and much prolonged in front. 

 In the frontal region the skull is massive and greatly strengthened to sup- 

 port the large and lofty horn-cores which formed the central feature of the 

 armature. The huge, expanded, posterior crest, which overshadowed the 

 back of the skull and neck, was evidently of secondary growth, a practical 

 necessity for the attachment of the powerful ligaments and muscles that 

 supported the head. 



The trout part of the skull shows a verj high degree of specialization, 



and the lower jaws have been modified in connection with it. In front of 

 the premaxillaries there is a large massive bone not before seen in any ver- 

 tebrate, which has been called by the writer the rostral bone (os rostraU ). 

 It cover- the anterior margins of the premaxillaries, and its sharp inferior 

 edge is continuous with their lower border. This bone is much compressed 

 and its surface very rugose, showing that it was covered with a strong, 

 horny beak. It is a cartilage ossification, and corresponds to the pre- 

 dentary bone below. The latter, in this genus, is also sharp and rugose, 

 and likewise was protected by a strong, horny covering. The two together 

 closely resemble the beak of some of the turtles, and as a whole must have 

 formed a most powerful weapon of offense. 



The frontal bones are quite short, and early unite with each other and 



with the adjoining elements, especially those behind them. The frontal or 

 mom xxvn .;:: 



