4 Prof. 0. C. Marsh — Gigantic Ceratopsidee. 



The base of the skull has been modified in conformity with its 

 upper surface. The basi-occipital is especially massive, and strong 

 at every point. The occipital condyle is very large, and its articular 

 face, nearly spherical, indicating great freedom of motion. The basi- 

 occipital processes are short and stout. The basi-pterygoid processes 

 are longer, and less robust. The foramen magnum is very small, 

 about one-half the diameter of the occipital condyle. The brain - 

 cavity is especially diminutive, smaller in proportion to the skull, 

 than in any other known reptile. 



The excccipitals are also robust, and firmly cob'ssified with the 

 basi-occipital. The supra-occipital is inclined forward, and its ex- 

 ternal surface is excavated into deep cavities. It is firmly coossified 

 with the parietals above, and with the exoccipitals on the sides. The 

 post-temporal fossae are quite small. 



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 quadi-ato-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 squa- 

 mosal. In Ceratops, 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 posterior 

 extremity, but at its upper surface, as shown in Plate I. Fig. 1 

 This greatly strengthens the centre 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 maxillary. This virtually takes the place of the trans- 

 verse 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 I. Fig. 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 Ceratopsidee 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. 



