O. C. Marsh — Skull of the Gigantic Ceratopsidm. 505 



The quadrate is robust, and its head much compressed. The 

 latter is held firmly in a deep groove of the squamosal. The 

 anterior wing of the quadrate is large and thin, and closely 

 united with the broad blade of the pterygoid. 



The quadrato-jugal is a solid, compressed bone, uniting the 

 quadrate with the large descending process of the jugal. In 

 the genus Triceratops, the quadrato-jugal does not unite with 

 the squamosal. In Oeratops, which includes some of the 

 smaller, less specialized, forms of the family, the squamosal is 

 firmly united to the quadrato-jugal by suture. Above this 

 point, it shows a number of elevations, which are wanting in 

 Triceratops. 



The quadrato-jugal arch in this group is strong, and curves 

 upward, the jugal uniting with the maxillary, not at its pos- 

 terior extremity, but at its upper surface, as shown in Plate 

 XII, figure I. This greatly strengthens the center of the 

 skull which supports the horn-cores, and also tends to modify 

 materially the elements of the palate below. The pterygoids, 

 in addition to their strong union with the quadrate, send 

 outward a branch, which curves around the end of the max- 

 illary. This virtually takes the place of the transverse bone. 

 The latter is thus aborted, and is represented only by a small, 

 free ossicle resting upon the posterior extremity of the 

 maxillary. 



The lower jaw shows no specialization of great importance, 

 with the exception of the pre-dentary bone already described. 

 There is, however, a very massive coronoid process rising from 

 the posterior part of the dentary, which is well shown in Plate 

 XII, figure 1. The articular, angular, and surangular bones, are 

 all short and strong, and the splenial is comparatively slender. 

 The angle of the lower jaw projects but little behind the 

 quadrate. 



The unique characters of the skull of the Ceratopsidm are 

 especially the following : 



(1) The presence of a rostral bone, and the modification of 

 the pre-dentary to form a sharp, cutting beak. 



(2) The frontal horn-cores, which form the central feature 

 of the armature. 



(3) The huge, expanded parietal crest, 



(4) The epoccipital bones. 



(5) The aborted transverse bone. 



These are all features not before seen in the Dinosauria, 

 and show that the family is' a very distinct one. 



