36 . THE CEKATOPSIA. 



cavity at about the middle of its posterior border. Near the inner border the superior wall 

 of the orbit is supported by three more or less perpendicular pillars. The most posterior, 

 largest, and strongest of these is fornied by that buttress-like lamina already described as 

 being present on the superior wing of the alisphenoid and supporting from beneath the post- 

 frontals and the massive supraorbital horn cores. 



THE ANTERIOR NARES. 



Unlike the anterior nares in crocodiles, alligators, and most recent reptiles, the anterior 

 nares in the Ceratopsia are separated by an imperfect bony partition and open laterally instead 

 of vertically. They are broad, deep incisions between the premaxillaries and nasals. Poste- 

 riorly they communicate with the pterygoid fossae by large vacuities between the palatines and 

 the superior branches of the maxillaries seen at v in fig. 20. 



THE POSTERIOR NASAL OPENING. 



This is imperfectly closed in front and internally, though it apparently consisted of a single 

 opening near the base of and between the pterygoids and communicated with the narial orifice 

 through the partially inclosed canals situated opposite each other and one on the internal side 

 of either pterygoid. It was not inclosed by the pterygoids as in the crocodiles. 



THE POSTERIOR PALATINE VACUITIES. 



These are very large and greatly elongated openings between the maxillaries and are 

 divided medially by the slender vomers. They communicate above with the narial orifice 

 and below with the mouth. There is really no ossified false or true palate in the Ceratopsia, 

 such as is seen in most modern reptiles and more especially in the crocodiles and alligators, 

 where the palatines and inferior plates of the maxillaries are greatly developed, forming a con- 

 tinuous roof to the palate, interrupted posteriorly only by the elongated, lateral palatine 

 vacuities, separated by the broad, united palatines. In the Ceratopsia there is really no bony 

 roof to the palate, the oral cavity and narial orifice being confluent throughout almost their 

 entire length. 



THE ANTERIOR PALATINE FORAMINA. 



There are no true anterior palatine vacuities in the Ceratopsia. The premaxillaries and 

 the anterior portion of the maxillaries meet by their inner borders, entirely roofing over the 

 palate in this region, and the premaxillaries each send upward two strong pillars which give 

 support to their superior branches, the anterior extremity of the nasals and the nasal horn, 

 besides forming a considerable portion of the incomplete median nasal septum already men- 

 tioned. Although true anterior palatine vacuities are not present, the inferior surface of each 

 premaxillary is perforated by two (sometimes three) small foramina placed in longitudinal 

 series one anterior to the other. It seems scarcely possible that these small foramina shown in 

 fig. 28 can be remnants of the anterior palatine vacuities. 



THE BRAIN AND BRAIN CAVITY. 



Considering th^ size of the skull the brain is smaller in the Ceratopsia than in any other 

 known group of vertebrates. The external opening of the foramen magnum is large when 

 compared with the size of the brain. It is oval in outline, the transverse diameter being a little 

 the shorter. Just within the external opening of the foramen magnum two large foramina 

 (xn, fig. 31) enter the brain cavity, one on either side. These served to transmit the twelfth 

 pair of nerves. A little in front of these is a second and smaller pair of foramina (xi, fig. 31), 

 which I have interpreted as transmitting the eleventh pair of nerves, though Professor Marsh 

 has considered these nerves as entering the brain case together with the tenth through that 

 large foramen which is placed anterior to and a little above this and which I have interpreted as 

 the foramen lacerum posterius. Whatever the function of this foramen may be, it forms the 



