130 THE CEKATOPSIA. 



offensive and defensive weapons. The form and character of the rostral bone are well shown 

 in fig. 109. 



The predentary, fig. 110, is longer and more slender than the rostral. It is pointed anteri- 

 orly and posteriorly and is triradiate, presenting two superior lateral processes which overlap 

 the antero-superior margins of the dentaries and a single inferior median process which is 

 bifurcated distally and passes beneath the antero-inferior borders of the dentaries. 



The dentary is short and shows a number of large and small foramina arranged in a some- 

 what irregular longitudinal series on the external surface of the bone, as shown in fig. 41, mid- 

 way between the inferior and alveolar borders and commencing just in advance of the base of 

 the coronoid process. Between the base of the coronoid process and the anterior extremity 

 of the dentary the external surface is deeply concave antero-posteriorly instead of nearly straight, 

 as in some of the larger forms. 



The coronoid process curves strongly outward at the base. It is rather slender, of moderate 

 height, and much expanded antero-posteriorly at the summit. 



The articular, angular, and surangular, fig. 40, are closely applied to and interlocked with 

 one another in a somewhat complicated manner. They are not, even in the present specimen, 

 which represents a rather old individual, coossified either with the dentary or with one another. 

 The free condition of these elements, taken in connection with the open symphysis and the 

 free quadrate and shallow articular cup, might be taken as indicative at least of the possibility 

 of some lateral and fore-and-aft motion in the lower jaws. However this may have been, it 

 is quite certain that the jaws were not absolute^ rigid, though the manner in which wear has 



Fig. 110.— Predentary of type of Trlceralops prorsus Marsh, No. 1S22. Yale Museum. 1, Side view; 2, superior view; 3, inferior view, a, Ante- 

 rior end; o, upper border; d, groove for dentary; s, symphysis. One-eighth natural size. After Marsh. 



taken place on the teeth both in the upper and lower series is proof positive that in tne process 

 of mastication there was little or no lateral movement of the jaws one upon the other. 



From the inner side the dentary presents a regular longitudinal series of dental foramina 

 on its median surface, numbering one for each of the vertical series of teeth in the dental 

 magazine, which in the present instance amounts to thirty-two. 



Posteriorly the dentary is invaded by the deep and elongated mandibular fossa, which 

 is closed behind by the angular, surangular, and articular, and internally by the long and slender 

 splenial. Near the anterior extremity of the mandibular fossa two rather large foramina 

 pierce the walls of the dentary. 



The splenials, fig. 37, are very long and quite slender anteriorly, but broader behind, 

 where they form the inner walls of the mandibular fossae and are each pierced by a 

 large internal mandibular foramen which communicates with the mandibular fossa. 



The premaxillaries have the usual form. They send upward and forward two strong 

 buttress-like pillars which give support from beneath to the superior arm of the rostral and 

 the nasal horn core. A shorter buttress, not so stout, is directed upward and backward. 

 This reaches only about halfway to the nasals, and with its anterior and posterior projecting 

 lamina? forms an imperfect median nasal septum. 



The narial orifice is large and opens externally by two very large lateral openings bounded 

 above by the nasals and behind by the inferior processes of the nasals and the postero-superior 

 processes of the premaxillaries. The narial orifice is confluent below with the mouth. The 

 palatines and pterygoids did not form a closed palate. The vomers probably formed a long 



