THE SKULL. 23 



The Maxillakies. 



In all the Dinocerata, the maxiHaiy bones form a large portion of the 

 lateral surface of the skull. They contain all the teeth, except those of the 

 lower jaw, and also expand into the large median pair of osseous elevations, 

 or horn-cores. On the external lateral surface, the maxillarles unite above 

 with the frontals by suture ; below this, with the lachrymals, and further 

 down with the malar. This is well shown in tlie figure of Dinoceras 

 mirabile, Plate II, ni. In front, the maxillaries unite with the pre- 

 maxillaries by a nearly straight, and nearly vertical, suture. Above, 

 they join the nasals, as already described. 



Tlve large canine tusk is entirely enclosed in the maxillary, and in the 

 genus Dinoceras its root extends upward into the base of the maxillary 

 liorn-core. In all known Dinocerata, there is a diastema between the upper 

 canine and the pre-molars. The latter are small, and form with the molars 

 a continuous series. On their inner surface, the maxillaries send in strong 

 palatine plates, which meet on the median line. The maxillary is 

 perforated by a large antorbital foramen, the outlet of which is concealed, 

 in the side view of the skull, by a ridge extending upward in front of the 

 orbit. Its position is shown in figures 22-24, c, page 25. 



The Pkemaxillaries. 



The premaxillary bones are edentulous, and, even in young- 

 specimens, contain no teeth. These bones liave three distinct branches, 

 the largest of which extends well forwai'd below the anterior nasal 

 opening. The second branch also extends forward above this opening, 

 forming with the nasal its superior border, as shown in the tj'pe of 

 Binoceras mirahUe, Plate II, pin. The third branch is a horizontal plate 

 extending inward to the median line, where it joins its fellow, and thus 

 completes the anterior portion of the palate. 



The anterior free portions of the premaxillaries are well separated on 

 their palatal surface, but tliese bones meet somewhat in front of the anterior 



