46 
the dentary. It runs forward from a short distance in advance of the 
hinder end of the surangular, on the inner side of that bone, to a point 
on the dentary below the Meckelian groove, presumably about in line 
with the midlength of the dental magazine. In lateral aspect it is bent 
at one-third of its length from the posterior termination, being straight 
and inclined slightly upward in the hinder part, and horizontally straight 
in the two-thjrds forward length. Its greatest depth is at the bend whence 
it narrows forward and backward to its pointed ends. Viewed from 
above it has a flattened sigmoid curve resulting from its close application 
posteriorly to the convex curve of the inner border of the surangular, 
and anteriorly to the longitudinal concavity of the lowermost inner surface 
of the dentary. Superiorly, for nearly the whole of its posterior half- 
length, it is in contact with the lower border of the splenial. In Figure 
25B, representing the inner aspect of the right angular, the surfaces of 
contact of the bone With the three elements above mentioned are clearly 
indicated. 
Measurements of Right Angular of Edmontosaurus, Cat. No. 2289 {disarticulated skull). 
Mm. 
Length of bone preserved, measured along the inner curve 290 
Estimated total length 377 
Depth at bend 37 
Maximum horizontal breadth of sutural surface for surangular (max. thickness) . . 15 
Outer Openings of Skull. 
Supratemporal Fossce. These openings are of moderate size, and 
very close together on either side of the extremely narrow longitudinal 
parietal ridge. They are subtriangular in outline, more than twice as long 
as wide, narrowly rounded behind, and end squarely in front where they 
are widest. They are bounded externally by the postfrontal and squa- 
mosal (supratemporal arcade), posteriorly by the squamosal, anteriorly 
by the postfrontal and parietal, and internally by the parietal and squa- 
mosal. They are floored on their inner side by the parietal, prootic, and 
to a limited extent also toward the front by the alisphenoid. Infero- 
externally they open beneath the supratemporal arcade into the infra- 
temporal fossa, and are confluent infero-anteriorly with the orbital 
cavities. 
Infratemporal Fossce. The principal feature of these openings is their 
extreme narrowness in comparison with their height. Although narrow 
below they become still further reduced in their upper half where they are 
encroached on by the backward extension of the large postfrontals. Their 
lower end is within the jugal. Anteriorly the fossa are bounded by the post- 
orbital bar proper and the augmented postfrontal; their narrow upper 
end is confined by the postfrontal and squamosal, and posteriorly their 
margin is formed by the squamosal, quadrate, and jugal. They are nearly 
twice as long as the supratemporal fossa. 
Orbital Cavities. The orbits are the largest of the openings of the 
skull, the next in size being the narial opening. They are subcircular in 
outline with an antero-inferior extension downward and forward, the 
height slightly exceeding the length at midheight. The anterior margin 
is formed by the prefrontal, lachrymal, and jugal. Superiorly the opening 
is bounded by the prefrontal, frontal, and postfrontal, posteriorly by the 
