1904] Posterior crest of horned dinosaurs 



83 



The horn core, figure 3, found with the crest is presumably a 

 nasal one. It is straig-ht, and laterally compressed so as to be 

 lenticular in cross section presenting a sharp edge to the front and 

 rear. A somewhat similarly shaped nasal horn core has been de- 

 scribed by Cope under the name Monoclonius sphenocerus. One 

 side, that figured, is deeply channelled longitudinally, the other is 

 more regularly convex ; vascular markings are conspicuous on both 

 sides. There is apparently no great distortion, if any, of the 

 specimen, which is 30 centimetres long and imperfect at the tip and 

 below. ^ 



We may conclude from the above that Ctnitnisaurus apertus had 

 a broadly expanded squamoso-parietal crest composed mainly of 

 the coalesced parietals, the squamosals being confined to the 

 anterc-iateral edge of, and taking but little part in the formation 

 of, the frill. That the large oval fontanelles were included en- 

 tirely within the parietal part of the expansion and that epoccipital 

 bones were well developed, of which the hinder pair were greatly 

 modified so as to form large hooks or spurs of bone on the hinder 

 border. That a closely fitting integument was present, as is indi- 

 cated by the many impressions of blood-vessels on the upper sur- 

 face, with the probability that the projections of the periphery at 

 the sides and behind were sheathed in horn. 



The.'quamoso-parietal frill o{ Monochmiiis canadensis is re- 

 presented by a well preserved right squamosal, figures 4 and 6, 

 and part of the parietal, figures 5 and 7. With these were found 

 other parts of the skull, to which reference has been made in the 

 original description. 



The squamosal is plate-like, somewhat triangular in shape 

 with the apex of the triangle directed backward. The inner 

 border is concave in outline, the outer one convex and scalloped. 



1 he front border has two deep emarginations in its outer half- in 

 the inner half are the sutures for the jugal and postfrontal 'its 

 upper surface is smooth. Beneath is a deep pit, r, figure 6, which 

 received a process from the quadrate, and at a slightly lower level 



he outer end of the exoccipital probably effected a junction where 

 the broken surface is indicated at d. A shallow groove, f. figures 

 6 and 4, extends from the raised surface for the exoccipital to and 

 over the inner border to the upper surface where it ends; it be- 

 comes deeper and narrower near the border. There is a wide tri- 

 angular excavation in the inner front portion of the lower surface 

 with indications that the bone here overlapped the postlrontal to 

 some extent, the contact with the jugal being limited to a sm;dl 

 surface which would include the marginal pit shewn in fip-ure 

 4 at ^. ^ 



The parietal reached the squamosal from behind by means of 

 an attenuated lateral extension of which only the anterior extre- 



