THE SKULL. 



25 



The lachrymals form a part of the lower portion of the anterior border of the orbits. This 

 portion of the orbital border is much thinner and is less projected than that immediately above, 

 which is formed by the prefrontals. In front of the orbit the lachrymal is continued forward 

 between the prefrontal above and the jugal and maxillary below. The anteroinferior angle of 

 the lachrymal is lodged between the nasal and the superior branch of the maxillary, and just at 

 the union of these three elements there is in the type of Triceratops serratus a foramen which 

 passes between rather than through any of these bones. The position'of this foramen varies in 

 the different species; in general it is comparable with that of the infraorbital foramen in the 

 mammalia, and its function may have been similar in the two groups. The internal opening 

 of this foramen is partially bounded by the palatine. 



THE NASALS. 



In the skulls of old individuals the nasals of opposite sides are firmly united by suture. 

 In the types of Triceratops flabellatus and T. serratus, however, they are still separate. Along 

 the median line of the skull the sutural border is very thick throughout the entire length of the 

 nasals. The external surface of the nasals is regularly convex. Each nasal consists of a 

 broadly expanded posterior portion, an 

 elongated superior portion closely ap- 

 plied to, and in old age coossified with, 

 that of the opposite nasal, and a shorter 

 inferior branch, as shown in fig. 19, A 

 and B. The elongated superior branches 

 of the nasals form the roof of the nasal 

 passage anteriorly and support the nasal 

 horn, which, however, has its origin in a 

 distinct and single center of ossification 

 that does not coossify with the nasals 

 until late in life. At their anterior ex- 

 tremities the rtasals each send down- 

 ward a short process which overlaps the 

 superior border of the premaxillary. 

 The postero-inferior branch of the nasal 

 is shorter and more slender than the 

 superior. It is directed downward and 

 forward and overlaps the ascending pos- 

 terior branch of the premaxillary, which is wedged in between this branch of the nasal and 

 the maxillary. The free borders of the nasals form the superior, posterior, and most of the 

 inferior borders of the anterior nares, which open laterally. Posteriorly the nasals are over- 

 lapped by the anterior edges of the frontals, prefrontals, and lachrymals. The nasals pass far 

 back under the anterior border of the frontals and prefrontals, but the surface covered over by 

 the lachrymals is more limited. 



THE MAXILLARIES. 



The general outline of the maxillaries, as shown in fig. 22, is that of an irregular triangle, 

 of which the inferior border forms somewhat the longer side. Posteriorly the maxillary is 

 produced into a superior ascending branch and an inferior and horizontal branch. Anteriorly 

 and superiorly the maxillary has an extended articulation with the premaxillary, and supero- 

 posteriorly it is in contact with the jugal, the lachrymal and for a short distance with the nasal, 

 as shown in fig. 10. Internally it has an extended union with the palatine and the lachrymal, 

 as seen in fig. 20. The long inferior and posterior process of the maxillary is embraced at its 

 extremity by the anterior of the two inferior processes of the pterygoid, and supports on its 

 superior and external surface the flat and rather rudimentary transverse, which latter bone, as 



Fig. 19.— A, External view of right nasal of type of Triceratops flabellatus, 

 No. 1821, Yale Museum; B, internal view of same, a, Inferior process; 6, 

 process beneath nasal horn overlapping premaxillary; c, surface for contact 

 with premaxillary: I, surface for lachrymal; /, surf ace for frontal ; no, ante- 

 rior nasal opening; h, surface for support of nasal horn core; n, surface for 

 opposite nasal. One-eighth natural size. 



