34 THE CERATOPSIA. 



inferior surface of the anterior extremities of the premaxillaries. The external surface of 

 the rostral is very rugose, and in life was doubtless covered with a horny sheath which opposed 

 a similar covering on the predentary of the mandible. 



THE EPIJUGALS. 



These are small, conical dermal ossifications, one on the external side and at the inferior 

 extremity of each jugal. In young animals they are free, but in old age they become firmly 

 coossified with the jugals. They are blunt at the apex and triangular in cross section. The 

 external surface is very rugose, indicating that in life they were incased in a dense horny or 

 dermal covering. Inferiorly and superiorly the epijugals are expanded into thin plates covering 

 over the posterior border of the jugal and overlapping the quadratojugal. 



THE EPOCCIPITALS. 



Arranged about the periphery of the frill are a series of small, usually elongated triangular 

 ossicles called by Marsh the epoccipitals, though this name does not seem especially appro- 

 priate, since they have no connection with any of the occipital bones. They might more 

 appropriately have been called the epiparietals and episquamosals, since they are borne upon 

 and in old age become coossified with these bones. These elements are wanting in the genus 

 Torosaurus and perhaps also in some species that have been referred to Monoclonius. There 

 is a single large median one at the distal extremity of the parietals, placed transversely to the 

 longitudinal axis cf the skull, and the others are arranged at intervals of a few centimeters 

 on either side, along the external borders of the parietals and squamosals. In the type of 

 Triceratops serratus (No. 1823, Yale Museum) there were eight of these on either side of the 

 single median one, making seventeen in all, though the number evidently varied in the different 

 species, since in the type of Triceratops prorsus there were nine, on either side, or nineteen in 

 all. The median of these ossicles is somewhat the larger, but they continue of about equal 

 size until that near the upper border of the squamosal is reached, when they rapidly grow 

 smaller and terminate in a diminutive little ossicle situated on the anteroinferior angle of 

 the squamosal. These ossicles all present a pointed median apex, and from their surface mark- 

 ings they appear in life to have been covered with a horny substance. When in position they 

 give to the border of the frill a peculiar scalloped appearance, which during life was probably 

 even more pronounced, through the presence of the horny coverings. Whether functioning 

 primarity as ornaments or weapons, they must have imparted a very striking appearance 

 to this portion of the animal's anatomy. 



EXTERNAL OPENINGS IN CRANIUM. 



Although in the Ceratopsia the different bones of the skull are more completely ossified 

 than in most other reptiles and the external wall is as complete and continuous as in most 

 mammals, instead of having the different elements present only in a cartilaginous condition 

 or reduced to mere rods of bone loosely articulated and separated by wide vacuities, as is 

 generally the case among reptiles, nevertheless most of the more important cranial openings 

 found in the reptilian skull are still to be seen in the skulls of this group. 



THE SUPRATEMPORAL FOSSAE. 



These are two large openings, situated one on either side at the anterior extremity of the 

 parietal and between that bone and the squamosals. They are elliptical in outline, with the 

 antero-posterior diameter the longer, but are directed inward and forward at an angle of about 

 45° to the median line of the skull. At the supero-posterior border of each of these foramina 

 a number of deep canals or channels emerge and spread out over the surface of the parietals, 

 forming a complicated system of ramifying channels, while from the postero-inferior angle 

 of the fossa a single deep groove runs along the superior border of the squamosal, giving rise 



a Dinosaurs of North America, p. 210. 



