79 
postorbital and prefrontal and contributes to the formation of the orbital rim, 
but not to as great an extent as in the case of T. annectens or T. edmontoni. 
Posteriorly the frontals meet the anterior border of the coalesced 
parietals, to the full extent of their breadth, with a digitating suture. 
The postorbital is a triradiate bone with a stout anterior process 
which unites internally with the frontal; a long, thin, posterior bar which 
overlaps the anterior process from the squamosal; and a descending process 
which meets the ascending postorbital process of the jugal. The descending 
process is quite large in the superior three-fifths of its length; then it 
suddenly diminishes and continues as a small, thin bar which is overlapped 
an tero-in tern ally by the long, slender, ascending process of the jugal. 
The postorbital resembles that bone in Edmontosaurus regalis in that it 
develops a well-defined fold or pocket subsidiary to the orbital cavity. 
This pocket differs from that of the above-mentioned species in being 
smaller, situated at a lower level, and in having different proportions. The 
greatest diameter is supero-inferior, being almost three times the transverse 
diameter. Marsh makes no mention of such a pocket in the postorbital 
of T. annectens , but his illustration suggests the presence of a similar one. 
The parietals are thoroughly fused and resemble those of T. annectenSj 
except that they have a greater expansion anteriorly and form a consider- 
able part of the anterior border of the supratemporal fossa. 
The squamosal resembles that element in T. annectens , and, as in 
that species, sends a process forward which with the posterior process 
of the postorbital forms the supratemporal arcade. 
The quadrate is a long, vertically placed, transversely compressed 
bone. From its inner surface a large, thin flange is directed inward and 
forward for attachment with the pterygoid. When viewed from the 
side, in the articulated skull, it appears to be straighter than that element 
in T. annectens , thu being largely due to the fact that in the upper portion 
the anterior face is less convex and the posterior face less concave. Just 
below the midlength on the antero-external surface is a prominent excava- 
tion for the reception of the quadratojugal. This is more strongly defined 
than in the above-mentioned species, due to the greater size of the quadrato- 
jugal. The inferior condyle might be said to be made up of two articulating 
surfaces, a large, strongly convex, lower surface which articulates with 
the surangular and a small, flattish, inner surface which faces downward, 
inward, and somewhat backward and articulates with the articular. This 
surface is at a higher level than the main condyle. 
The quadratojugal is a thin discoid bone of considerable size. It 
runs to a very thin edge anteriorly where it is overlapped, to about one-half 
its extent, by the jugal, but is thicker on its posterior margin where it 
overlaps the emarginated, antero-external border of the quadrate. It 
separates the jugal and quadrate, except for a slight contact between these 
bones at the extreme postero-superior tip of the jugal. 
The jugal is of the general hadrosaurian shape, but is long and slender. 
Its length is more than four times its greatest breadth, whereas in T. 
annectens the length is slightly more than three times the greatest breadth. 
Posteriorly it is particularly slender and unites with the jugal in its supero- 
posterior extremity. This slenderness of the posterior portion is due 
to the great excavation of its upper surface which also increases the length 
of the infratemporal fossa. 
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