43 
which apparently passes forward on the inner side of the flange and is 
supported below by the narrow horizontal shelf between the base of the 
flange and the sutural surface for the angular. 
The upper surface of the bone externo-posteriorly is shallowly excavated 
for the reception of the greater portion of the lower end of the quadrate, 
the remaining part of the cotylus being supplied by the articular. The 
contribution given to the cotylus by the surangular passes inward and up- 
ward on to the flange and is deflned in front by a low, rounded ridge 
which runs transversely outward from the flange near its anterior ending 
to the outer border slightly in advance of the postero-exterior angle of 
the main portion of the bone. 
Measurements of Right Surangular of Edmontosaurus, Cat. No. 2289 {disarticulated 
skull). 
Mm. 
Length of bone measured along the curve of its lower surface from the front border 
to the termination of the posterior extension 290 
Breadth at midlength 81 
Height at midlength from lower surface to top of median flange 69 
Backward extension of surangular beyond infero-posterior termination of dentary. . 147 
Thickness, from lower to upper surface, of main portion of midbreadth slightly 
behind midlength 31 
Articular. (Ar.). Figures 20 and 23. In this species the articular 
is as yet imperfectly known. In the type skull. Cat. No. 2288, it is repre- 
sented in the right mandibular ramus by a small fragment in place between 
the surangular and the splenial above the posterior termination of the 
angular. In the disarticulated skull, Cat. No. 2289, the only part of it 
A 
Figure 23. Portion of left articular of Edmontosaurus, Cat. No. 
2289, in place on the splenial; j natural size. A, external aspect; B, 
anterior aspect in outline; C, posterior aspect in outline. Ar, articu- 
lar; q, surface for contact with quadrate; sa, surface for surangular; 
/Sp, splenial; sp, surface for splenial. 
remaining is a piece of irregular shape, 55 mm. in maximum length, 51 mm. 
in depth behind, and 21 mm. in breadth antero-superiorly, adhering to 
and in its proper relative position to the outer posterior surface of the 
left splenial as shown in Figure 23. The fragment in the type skull, so 
far as its smallness permits, corroborates the larger portion in the second 
skull as regards shape and position. 
