38 
The prefrontal is a triangular bone that forms the orbital rim between 
the lachrymal in front and the postorbital behind. Internally it unites 
strongly with the frontal and the nasal as shown in Figure 8 A. The post- 
orbital, called the postfrontal by Lambe, Brown, and others, may possibly 
represent a complex of the two elements, as in the theropodous dinosaurs. 
The alisphenoid, however, abuts against it internally, and from an exam- 
ination of detached hadrosaurian postorbital bones, a cupped depression 
or pit is found for the articulation of this end of the alisphenoid. In those 
dinosaurian skulls in which prefrontal, postfrontal, and postorbital bones 
remain distinct this cupped depression is always on the postorbital and 
for that reason, and also because the supratemporal arcade in the reptilia 
is usually formed by the united processes of the postorbital and squamosal 
bones, it would appear more proper to identify this element as the post- 
orbital. It unites anteriorly above the orbit with the prefrontal, internally 
Figure 9. Skull of Lambeosaurus lambei Parks. Type, No. 2869, Geol. Surv., Can. Viewed 
from the right side. Ar, articular; Da, dentary; Ept, ectopterygoid; Fr, frontal; J, jugal; L, lach- 
rymal; Mx, maxillary; N, nasal; No, external nares; Opot, paraoccipital process; Pd, predentary; 
Pal, palatine; Pmx, premaxillary; Par, prearticular; Pof, postorbital; Prf, prefrontal; Pt, pterygoid; 
Q, quadrate; Qj, quadratojugal; Sa, surangular; Sq, squamosal. About one-seventh natural size. 
with the frontal, and slightly with the parietal, but sufficiently to exclude 
fully the frontal from participation in the anterior boundary of the supra- 
temporal fossa. The posteriorly directed branch meets the squamosal, 
forming the relatively wide supratemporal bar. The posterior widely 
bifurcated end strongly overlaps the ascending process of the jugal by a 
long squamous suture to form the relatively slender postorbital bar. 
