32 
or about two-thirds of its length from the upper end. Above the lower 
end it rises rapidly with a concavely curved edge to its apex whence it 
ascends less rapidly with a nearly straight edge to the head. Throughout 
it partakes of the general curve of the main portion of the bone so that its 
interno-posterior face is concave. Between the base of the flange and the 
incurved anterior border the inner surface of the bone is concave; a con- 
cavity equally deep but extending for a shorter distance above and below 
the midlength occurs behind the flange between its base and an incurve 
of the posterior border. 
The lower end of the quadrate has its greatest diameter transverse 
and fits into the mandibular cotylus jointly contributed to by the sur- 
angular and the articular. When seen from below it is subtriangular in 
outline with the apex of the triangle inward, the base convex outward, 
and the sides concave. The larger outer part of the lower surface is 
convex and faces directly downward in contact with the surangular, the 
inner and smaller apical portion of the surface is almost flat, looks down- 
ward and backward, and fits against the articular, the combined facets 
being the quadrate’s contribution to the mandibular hinge. The inner 
articular extension of the lower end acts as a pedestal for the ascending 
flange. 
A roughened surface on the inner front of the bone, extending for a 
short distance downward from the head, marks the close sutural contact 
of the short, stout process or spur descending from the squamosal in 
advance of the pit in that element into which the head of the quadrate 
fits. 
Above the narrow, curved surface which marks the overlap of the 
quadrato-jugal, a limited, roughly striated area on the inner side of the 
anterior border indicates the surface of contact with the jugal. 
The extent of the overlap by the pterygoid is well marked on the 
postero-internal face of the flange by a surface which extends downward 
from the top of the flange for more than two-thirds of its length. This 
surface extends over the flange from its edge and is roughened by striations 
which are approximately at right angles to the free edge. At its lower 
end it broadens abruptly below a conspicuous sunken area in the inner 
posterior marginal concavity already described. 
The head of the quadrate in an undetermined species of Trachodon 
has elsewhere^ been referred to as movable in the cotylus of the squamosal. 
There can be no doubt that it was firmly fixed in position and immovable 
in the genus now under description. Tlie fact that a heavy process from 
the squamosal descended for some distance on and suturally united with 
the anterior border of the quadrate below its head is sufficient to prove 
that the quadrate was stable at its upper end. The very extensive lapping 
contact between the quadrate and the pterygoid would in itself be sufficient 
to prevent any movement of the former element. The direct contact 
of the jugal with the quadrate was slight and can have added little to the 
strength of the close union of the jugal with the quadrato-jugal, and the 
latter with the quadrate. 
^Memoirs of the American Museum of Natural History, new series, vol. I, pt. I, “Crania of Tyrannosaurus 
.nd Allosaurus,” by Henrs' Fairfield Osborn, 1912, p. 18, fig. 13. 
