120 THE CEKATOPSIA. 



The alisphenoid differs materially in the type of the present genus from that in the type 

 of Sterrholophus , a as will be readily seen by a comparison of figs. 9 and 27. Instead of stopping 

 a little short of the anterior opening of the olfactory foramen as in the last-mentioned genus, 

 it is carried considerably in advance of that opening, which in the present specimen is divided 

 by a strong median septum into two openings, the olfactory nerves leaving the brain case by 

 two lateral foramina in the type of Triceratops instead of by a single median one as in the type 

 of Sterrholophus, 11 differences which should certainly be regarded as of generic importance if both 

 skulls were adult. Since, however, the type of Sterrholophus pertained to a young individual 

 it is probable that the median septum was present as cartilage and was lost in maceration. 

 It is very unlikely that there was in any of these dinosaurs a single olfactory nerve. 



The posterior portion of the vomers appears in position wedged in between the vertical 

 plates of the palatines, while at their extreme posterior end they divide and embrace the anterior 

 and inferior edge of the alisphenoid, which shows a small median foramen just beneath the 

 olfactory foramina. Beneath and posteriorly the vomers join the ascending branches of the 

 pterygoids in a W-shaped articulation, as shown in fig. 25 (p. 28). Only the posterior portion 

 of the vomers is preserved. 



The palatines are each composed of two broad, thin vertical plates of bone, one directed 

 antero-posteriorly, and the other transversely. The transverse plates are well shown in fig. 27, 

 while the longitudinally directed plates are better seen in fig. 24. Posteriorly the longitudinal 

 plates of the palatines join the pterygoids and together they form the posterior lateral walls 

 of the palate. Beneath, the palatines overlap a considerable portion of the posterior and 

 inner surface of the maxillary concealing a number of the dental foramina. There is a large 

 circular foramen between the palatines and pterygoids just above the superior border of the 

 maxillary. The function of this I have been unable to determine. Above, the longitudinal 

 blades of the palatines overlap the vomers, the superior branches of the pterygoids and clasp 

 between them the inferior edge of the alisphenoid, while the external portions of the superior 

 borders of the transverse blades are produced upward until they nearly or quite meet two 

 opposing dependent processes from the anterior extremity of the postfrontals and surround 

 two large vacuities shown at / in fig. 27, placed one on either side, which afford direct 

 communication between the narial orifices and the lateral temporal fossas. 



On the right side the entire external wall of the skull had weathered away, and when the 

 matrix filling the capacious lateral temporal fossa was removed the relations of those elements 

 that form the internal walls of that fossa were clearly revealed, as shown in fig. 24. The broad 

 superior and posterior blade of the pterygoid is seen to curve outward and backward and to 

 pass beneath the thin superior blade of the quadrate, while, as shown in the same figure, the 

 slender inferior posterior blade runs backward along the inner surface of the maxillary, curving 

 quite around the posterior extremity of the inferior branch of the latter and articulating with 

 the rudimentary transverse bone or ectopterygoid. The latter element is reduced to an elongated' 

 flat plate of bone, broad and rounded behind and pointed in front, thickened in the middle 

 and thin at either end and fixed to the upper external surface of the inferior branch of the 

 maxillary. 



Above and in front the postfrontals appear intercalated between the alisphenoids and the 

 frontals and prefrontals. .In front there is a large cavity filled with matrix between the pre- 

 frontals and postfrontals and behind this the postfrontals are much thickened and are invaded 

 by a number of large cavities separated by strong partitions of bone. These postfrontal cavities 

 are present in all the larger members at least of the Ceratopsia, and they doubtless had their 

 origin in the application of that well-known mechanical principle or device, so often exhibited 

 in the organic world, by which strength is combined with lightness. Posteriorly and superiorly 

 the alisphenoid sends upward and outward a powerful buttress-like blade which acts as a 

 strong pillar, giving support to the postfrontals and the enormous supraorbital horn cores. 

 At the base of this pillar the optic foramen and foramen rotundum are seen separated from 

 the foramen ovale by a conspicuous prominence, while in front of these are the other smaller 

 foramina shown in the figure, the functions of some of which are at least doubtful. 



a Triceratops flabellatus, No. 1821, Yale Museum. 



