56 
slightly in advance of the middle of the magazine. A narrow, flattened 
surface beneath the Meckelian groove marks the contact with the missing 
angular. It would appear from the character of this surface that the 
angular probably extended forward to the midlength of the dentary. The 
dental foramina, one for each vertical tooth series, are arranged in a row 
following the lower curve of the dental magazine. A few irregularly 
placed foramina are present on the upper external surface of the dentary. 
The articulated elements forming the post-dentary part of the ramus are 
unusually short and stout. These have an anterior-posterior length of 
about one-fourth the total length of the jaw. The surangular, the largest 
of these bones, has an irregular shape that may best be described as con- 
sisting of a narrow anterior vertical portion, and a larger transversely 
expanded posterior portion that at its posterior end is obliquely truncated 
with an inwardly directed hook, which is missing in this specimen. The 
surangular articulates in front with the dentary, postero-superiorly with 
the articular, and internally with the prearticular and angular. The 
vertical and horizontal anterior ends of the surangular pass within the 
dentary, the former lapping along the inner side of the external wall of the 
coronoid process, and when complete rising to fully one-half its total height. 
The horizontal portion is broadly underlapped by the dentary and the 
floor of the mandibular fossa is continued back on the upper surface of the 
surangular for nearly one-half its length. The bone behind the fossa is 
crossed by a low, rounded, diagonally developed swelling, posterior to 
which the bone is shallowly cupped to form the cotylus of the jaw for the 
articulation of the quadrate. 
The articular, although present, cannot be clearly differentiated in this 
specimen. The prearticular (splenial of authors) is a thickened bony 
plate that forms the upper inner margin of the posterior mandibular fossa 
(Plate XII). In contact with the articular and surangular posteriorly it 
extends forward to, and embraces, the thin, pointed, posterior projection 
of the dentary behind the tooth magazine. A thin, pointed anterior 
projection continues forward beneath the magazine, terminating in this 
specimen at a point in line with the fifth vertical row of teeth, but in speci- 
men No. 8500 it continues as far as the tenth vertical tooth row. This 
process, with the anterior portion of the angular, forms a covering for 
Meckel’s groove and that fact may account for its previous designation 
as the splenial. Elsewhere (page 42) evidence is presented showing that 
this bone cannot be other than the prearticular, and that in the Hadro- 
saurid® the splenial is probably absent. The lower border of the pre- 
articular rests for the greater part of its length upon the underlying sur- 
angular, and was apparently slightly in contact along its lower internal 
surface with the missing angular. 
Teeth 
The teeth of this specimen are to be observed only in the dentary, 
and their finer details are not well preserved. In composition, implanta- 
tion, and succession they conform fully to the usual arrangement of the 
teeth in the Hadrosaurid®. The inner enamelled tooth surfaces are 
nearly lozenge-shaped, being relatively narrower and longer than in the 
much larger Edmontosaurm. They are largest in the central part of the 
magazine. The upper ends of the teeth are acutely rounded and slightly 
