or homed Dinosaurs, of North America. 169 



connection with it. In front of the premaxillaries, there is a 

 large, massive bone not before seen in any vertebrate, which 

 I have called the rostral bone (os rostrate). It covers the 

 anterior margin 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 dermal ossifica- 

 tion, and corresponds to the pre-dentary bone below. 



The latter, in Triceratops, is also sharp and rugose, and like- 

 wise was protected by a strong, horny covering. The two 

 together closely resembles the beak of some of the turtles, and, 

 as a whole, must have formed a most powerful weapon of 

 offense. 



In one skull figured (Plate I, figures 1-2), the rostral bone 

 was free, and was not secured. This was also true of the 

 pre-dentary bone and the nasal horn-core. Hence, these parts 

 are represented in outline, taken from another specimen in 

 which they are all present, and in good preservation. In 

 another skull represented (Plate I, figure 4, and Plate II, 

 figures 1-3), the rostral bone and nasal horn-core are in 

 position, and firmly coossified with the adjoining elements. 



The premaxillary bones are large, and much compressed 

 transversely. Their inner surfaces are flat, and meet each 

 other closely on the median line, In old specimens, they are 

 firmly coossified with each other and with the rostral bone. 

 Each sends upward a strong process to support the massive 

 nasals. Another process, long and slender, extends upward 

 and backward, forming a suture with the maxillary behind, 

 and uniting in front with a descending branch of the nasal. 

 The premaxillaries are much excavated externally for the 

 narial aperture, and form its lower margin. They are entirely 

 edentulous. 



The maxillaries are thick, massive bones of moderate size, 

 and subtriangular in outline when seen from the side. Their 

 front margin is bounded mainly by the premaxillaries. They 

 meet the prefrontal and lachrymal above, and also the jugal. 

 The alveolar border is narrow, and the teeth small, with only 

 a single row in use at the same time. 



The nasal bones are large and massive, and greatly thickened 

 anteriorly to support the nasal horn-core. In two of the skulls 

 figured, these bones are separate, but in older individuals, they 

 are firmly coossified with each other and with the frontals. 

 The nasal horn-core ossifies from a separate centre, but in 

 adult animals, it unites closely with the nasals, all traces of the 

 connection being lost. It varies much in form in different 

 species. 



