1917] The Ottawa Naturalist. 67 



phus, from the Belly River formation of Alberta, if the skull in the 

 Hadrosaurida 1 * can be considered a criterion of the size of the animal 

 as a whole. 



In the paratype the canium proper (brain-case), the squamosals. 

 postfrontals, prefrontals, lachrymals and nasals are preserved together, 

 the other elements of the skull (with the exception of the premaxillar- 

 ies, predentary, vomer, and right articular which were missing) were 

 all found in a disarticulated state, free from each other and with 

 practically no distortion. In the type skull (figure II) the pre- 

 maxillaries are in position, the vomer is partially preserved, but the 

 predentary is badly damaged. From the two specimens, therefore, we 

 have full information relative to all the elements of the Edmontosaurus 

 skull except the predentary and the vomer. 



The paratype reveals the exact shape of the brain cavity and the 

 position of the cranial nerves. In it are preserved without distortion 

 the palatines, pterygoids, and ectopterygoids, three elements of which 

 little has hitherto been known in the Hadrosauridae. 



In plates II and III, two aspects of the skull are given showing 

 the relative position to each other of the elements seen from these 

 particular viewpoints. 



The skull of Edmontosaurus is large and massive, triangular in 

 outline as seen from the side, high posteriorly, and narrowing down to 

 the front. As viewed from above it is broad behind and in front, and 

 greatly constricted behind the snout. Its posterior height is greater 

 than its half-length. Its posterior breadth slightly exceeds the full 

 lateral expansion of the snout, and is a little less than its half-length. 

 The orbit is large, the quadrate long, and the great development of the 

 premaxillarv bones in front, to form the horizontally expanded snout, 

 is remarkable. Viewing the skull from the side one is impressed by 

 the depth and robustness of the mandible. 



The principal bones of the skull with some of their main char- 

 acteristics are briefly as follows: 



Frontal. Rather flat, of irregular shape, longer than broad, and 

 entering narrowly into the formation of the orbital rim. Posteriorly 

 it meets the parietal, externo-posteriorly the postfrontal, and anteriorly 

 the nasal and prefrontal. 



Postfrontal. Of considerable size, gibbously protrudent out- 

 ward, somewhat triangular in superior aspect as well as when viewed 

 from the side. Is in contact with the frontal, parietal, squamosal and 

 jugal, extensively overlapping the squamosal. It forms the posterior 

 curve of the orbital rim. A remarkable feature of this bone is the 

 development within it of a deep, pocket-like recess leading back from 

 the orbital cavity. Following the presence of this large recess the lateral 



*The name Hadrosauridae proposed by Cope in 1869 (1871) has precedence 

 to Trachodontidae used by Lydekker in 1888 and later by Marsh in 1890. 



