participation in the boundary of the foramen magnum. Lambe, 1 how- 
ever, believed that the supraoccipital entered into the boundary of the 
foramen, but in Kritosaurus incurvimanus Parks 2 3 also finds the supra- 
occipital excluded from the foramen boundaries. 
Viewed from the rear, the squamosals are especially high, with their 
lower borders at the centre resting upon the supraoccipital and exoccipital, 
but passing from a superior to an anterior position as they continue out- 
ward toward the distal extremities of the paraoccipital processes. 
The foramina of the brain case in the Hypacrosaurus skull, so far as 
they can be observed, do not appear to differ materially in arrangement 
from those of the other described genera. 
Comparative Measurements of Skulls of Hypacrosaurus Altispinus 
No. 8501, 
Geol. Surv., 
Can. 
No. 8500, 
Geol. Surv., 
Can. 
Greatest length of skull between perpendiculars 
Mm. 
725* 
785* 
720 
695 
385 
305 
310 
260 
155 
220 
575 
340 
Mm. 
Greatest length of skull, tip of beak to terminal end of crest 
Greatest length of skull, tip of beak to posterior end of squamosals.. 
Greatest height of skull with lower jaws 
Greatest height of skull, bottom of ramus to orbital rim 
Greatest height of crest above orbital rim 
Greatest length of quadrate 
Greatest width of premaxillaries at beak 
Greatest width of crest at base above centre of orbits 
Greatest width across paraoccipital processes 
194 
Length from tip of beak to centre of anteiior orbital rim 
Length of maxillary 
360 
Mandible 
The right ramus, except for the loss of the angular and minor portions 
of the posterior extremities of the surangular, articular, and prearticular, 
is practically uncrushed and in a good state of preservation. The jaw is 
unusually deep and massive throughout. The edentulous portion in 
front of the tooth magazine is short, strongly deflected ventrally, with a 
broad, spout-like symphysial shelf whose upper surface forms nearly a 
right angle with the thinner, vertically directed, nondentigerous portion. 
The coronoid process is robust, high, with the anterior border of the upper 
end expanded and strongly overhanging. In profile the forward end of 
the dentary, as in all other helmet-crested members of the Hadrosauridse, 
is strongly decurved. 
In the dental magazine 38 vertical rows of teeth can be counted, and 
there may be one or two more in the complete series. In the second 
specimen, No. 8500, there are 40 vertical rows of teeth. The dental 
magazine is unusually deep and thick. The dentary is deeply excavated 
posteriorly by the mandibular fossa, from which Meckel’s groove narrowly 
leads forward on the infero-internal side to entirely disappear at a point 
Kieol. Surv., Can., Mem. 120, 1920, p. 12. 
2 University of Toronto Studies, No. 11, 1920, p. 17. 
3 20 mm. added for missing tip of beak. 
