44 
The portion of the articular preserved in the disarticulated skull, 
although imperfect behind and possibly in front gives the depth and 
thickness of the bone apparently where it is stoutest. It is thinnest 
below and rises on its inner side slightly above the upper border of the 
splenial. Outwardly it displays a flattened surface directed obliquely 
downward, for attachment to the surangular, and having a depth equal 
to about two-thirds of the total depth of the bone. Above this surface 
is the remaining one-third of the depth of the bone directed outward, 
and supplying a free surface which in its anterior part is slightly concave 
and constitutes the small contribution of the articular to the mandibular 
cotylus. The narrow lower border of the articular fits into the groove 
in the surangular mentioned in the description of that bone as occurring 
above the posterior end of its surface for the attachment of the angular. 
Continuing backward the articular probably rose still higher above the 
upper border of the splenial, as restored in Figure 20, reliance being placed 
to some extent on the shape of the articular in Gryposaurus. The articular 
in advance of its contribution to the cotylus, in view of the fact that there 
is a space left between the splenial and the surangular when these bones 
are in position, maj^ have continued forward as a moderately thin bone 
between the inner vertical face of the flange of the surangular and the 
concave outer surface of the splenial, and supported below by the hori- 
zontal shelf of the surangular. However, the possibility of the presence 
of a prearticular should not be overlooked. 
Figure 24. Left splenial of Edmontosaurus, Cat. No. 2289; i 
natural size. A, outer view; B, inner view; an, surface for angu- 
lar; ar, surface for articular; dn, surface for dentary. 
Splenial. {Sp.). Figures 20 and 24^ This element is a moderately 
thin plate of bone of about the same general thickness as the angular but 
deeper and shorter, and is in contact with the angular, the dentary, and the 
articular, interiorly with the angular, antero-externally with the dentary, 
and postero-externally with the articular. 
It is deepest at about one-third of its length from the front where a 
thin process, developed from the superior border, curves outwardly over 
the supero-internal termination of the dentary behind the dental magazine. 
