41 
of a vertical median septum. This nasal chamber occupies the greater 
part of the crest within, is flanked outwardly by the premaxillary and 
nasal bones and is somewhat over 150 mm. in height, and narrow from 
side to side, with a fore-and-aft diameter about three-fifths the height. 
An exit from the chamber is indicated externally by the greater convexity 
of the crest laterally in an area surrounding the narrow central vacuity. 
The Stephanosaurinid form of the external nares of Corythosaurus and 
Cheneosaurus points to the presence of a nasal chamber in these genera also.” 
Beneath the above-described chamber, the palatal surface also arches 
upward and it appears very probable there may be openings through could 
the specimen be prepared sufficiently to show them. 
A third specimen, No. 8503, in the Geological Survey collections, 
consisting of a considerable part of a skeleton of which only the skull 
has been prepared, is provisionally identified as belonging to this same 
species. The surfaces of the skull and especially of the crest are much 
abraded and eaten away, probably before entombment, and the posterior 
extension of the crest is missing. This skull is of interest in having, at the 
place where the elongated posterior extension; would attach, a vertically 
elongated aperture that apparently leads into the nasal chamber described 
above, and it suggests the probability that this passage continued still 
farther backward within the posterior premaxillary extension. 
I fail to detect any divisional septa, but may this air passage not be 
analogous to the “tube-like passages” described 1 by Parks in the posteriorly 
elongated crest of Parasaurolophusf It further suggests that the upper 
longitudinal half, at least, of the Parasaurolophus crest is composed entirely 
of the premaxillse instead of being formed by the nasals as these bones 
were provisionally determined. After a study of the skulls of several 
crested hadrosaurian genera in the Canadian Geological Survey collections, 
it seems quite certain that the longitudinal half of the Parasaurolophus 
crest is composed of the nasals instead of the frontals, as tentatively identi- 
fied by Professor Parks. Although Parasaurolophus has a remarkable 
development of the crest, in the lack of positive evidence, I see no reason 
for regarding it as fundamentally different in composition from those 
other members of the crested Hadrosauridse in which the structure is now 
so fully known. In none of these forms do the frontals enter into the 
formation of the crest; rather, as has been shown, these bones are greatly 
shortened antero-posteriorly, and have their anterior ends specially modi- 
fied by a deep vertical suture in order to give the necessary anchorage for 
the extensive premaxillary-nasal crest. Parks is certainly in error in 
regarding all the lateral area above and in front of the orbit as being com- 
posed of the frontal. If this were true the prefrontal has entirely dis- 
appeared and the lachrymal has assumed a position that has no parallel in 
the reptilia either recent or extinct. The element identified as lachrymal 
is surely the upper extremity of the superior maxillary process, and when 
other specimens are found in which the sutures can be seen, the lachrymal 
will undoubtedly be found occupying its proper position within the border 
of the orbit. The notching of the suture at the top of the jugal is exactly 
as it unites with the lachrymal in several other hadrosaurian crania. 
1 University of Toronto Studies, No. 13, 1922, pp. 10, 11. 
