27 
alveolar border, is much longer than the sloping sides, which descend 
concavely from a broadly curved apex. It is laterally compressed and 
thin above, and thick along its lower length. The inner face is as a whole 
rather flat in great contrast to the varied relief of the outer one. Exter- 
nally the bone is most protrudent, and thickest, at about midlength at 
a distance above the alveolar border equal to about one-sixth of its maximum 
height. From here extends upward the rugose surface of attachment of 
the front end of the jugal, the bone thinning rapidly upward. From the 
lower, overhanging edge of the surface for the jugal a robust ridge runs 
horizontally backward with diminishing strength to near the end of the 
bone. The surface between the ridge and the alveolar border is vertically 
concave. In advance of the surface for the jugal the external face is 
tumid upward from the alveolar border until on approaching the antero- 
superior border it becomes vertically concave in a marginal depressed 
area in which lay the ascending lower limb of the premaxillary. This 
area gains in width and in the amount of its concavity as it proceeds 
forward causing the anterior end of the bone to be thin-edged in front and 
sharply angulated supero-externally. Another concave area, still more 
pronounced in its depression, occurs in the posterior half of the bone 
between the shell-like upper surface of the ridge and the postero-superior 
border. Unlike the anterior concave area this posterior one is widest 
next to the surface for the attachment of the jugal and diminishes rapidly 
backward leaving the hinder end of the bone thick and robust. The 
bone is thin in the apical region, presents a flatly convex surface outward, 
and is sharp-edged above. Anteriorly this apical surface descends into 
Figure 13. The left maxillary, palatine, pterygoid, and ectopterygoid of Edmontosaurus, 
Cat. No. 2289, in position relative to each other to show extent of contact; | natural size; external 
aspect. Ept, ectopterygoid; Mx, maxillary; I, surface for lachrymal; j, surface for jugal; Pal, 
palatine; pnix, surface for lower limb of premaxillary; Pt, pterygoid; q, surface for quadrate. 
the antero-superior marginal depression for the reception of the pre- 
maxillary limb; posteriorly it is separated from the postero-superior 
concave area by a deep, vertically directed groove which emarginates the 
superior border behind the apex. The antero-superior portion of the 
apical surface is in close contact with the inner surface of the lachrymal. 
Below the lachrymal contact the surface for the attachment of the jugal 
