21 
parietal, externo-posteriorly the postfrontal, and anteriorly the nasal and 
prefrontal. Postero-externally it reaches the anterior margin of the 
supratemporal fossa at about the latter’s midbreadth. Externally toward 
the front it extends outward between the postfrontal and prefrontal, and 
contributes narrowly to the formation of the orbital rim. The prefrontal 
and nasal together form an angular emargination of the front border, the 
extent of contact with the nasal being about one-third of that with the 
prefrontal. As viewed from below the frontal meets the prefrontal to the 
full extent of the latter’s breadth which is equal to about three-fifths of the 
breadth of the frontal, the line of suture between the two running trans- 
versely inward from the orbital rim with a strongly zigzagged course. 
Between this contact and the longitudinal midline of the skull the frontal 
extends forward thinly beneath the nasal to a point nearly as far advanced 
as the supero-anterior edge of the prefrontal, the full fronto-nasal lapping 
length being about 111 mm. Beneath the nasals the frontals meet along 
the midline except for a short distance in front. 
Postfrontal. (Pof.) Figures 3, 4, 5, 6, 7, 8, and 26. The postfrontal 
is a conspicuous bone of considerable size and is remarkable in that it 
develops a large fold or pocket subsidiary to the orbital cavity. Seen 
from above its outline is irregularly triangular with the apex of the triangle 
directed outward, the long base being greater than either of the other two 
sides. In lateral aspect its outline may also be said to be roughly triangular 
with the apex downward. 
For one-half its length internally it is in contact with the frontal in 
a zigzagged suture extending from the centre of the upper curve of the 
orbital rim to the centre of the anterior margin of the supratemporal fossa. 
The posterior half of its length internally forms the outer half of the an- 
terior margin of the supratemporal fossa and contributes largely to the 
formation of the outer margin of that opening. Overlapping the squamosal 
to near the posterior end of the supratemporal fossa it constitutes with 
that bone the supratemporal arcade separating the supratemporal from 
the infratemporal fossa. 
Curving outward and downward and narrowing as it descends the 
postfrontal is gibbous externally to a marked degree and encloses within 
itself a large pocket which is a backward extension of the orbit and lies 
exterior to the postfrontal contribution to the postorbital bar. This 
pocket, opening directly forward, relegates the upper part of the post- 
orbital bar to a position within the orbit, well removed from the exterior 
surface of the skull. The presence of this pocket occasions modifications 
of shape in the postfrontal bone, not previously described, so far as the 
writer is aware, in any known member of the Hadrosauridse. 
The excavation of the postfrontal bone to form the postorbital pocket 
is extensive, measuring fully 115 mm. in fore-and-aft depth, and leaves the 
enveloping walls thin, particularly on the inner side, where over a con- 
siderable area the bony tissue is only about 1 mm. thick. In the external wall 
a thickness of from about 4 to 7 or more mm. is attained. In the sweeping 
inward curve infero-posteriorly the thickness averages about 5 mm. The 
excavation in its backward extension even enters for a short distance 
that part of the bone which overlaps the squamosal. Both in the roof 
and floor of the pocket the bone becomes thicker, especially so in the 
former on approaching the frontal suture; in the latter the thickening 
