43 
relationship with adjacent bones, for it is found not only in the primitive 
reptilian jaw, but also in numerous members of the dinosauria, notably 
the Camptosauridse, Stegosauri dae, and Ceratopsidse. So far as I am able 
to determine, the splenial has never been found in any reptile, recent or 
extinct, in contact with the articular, nor has it ever been known to occupy 
such a posterior position in the ramus as is necessary if the earlier identifi- 
cation of this bone should prevail. Since this and other rami before me 
show the angular and prearticular forming the covering for the greater part 
of Meckel's groove, with no trace forward of another element, it would 
seem that the splenial lias disappeared in the Hadrosauridse. However, 
should it later be found to be present, it can exist only as a very small 
elongated bone that would be invisible from a lateral aspect. 
Figure 10, Right ramus of Lambeosaurus lambei. Type, No. 2869, Geol, Surv., Can. Inter- 
nal view, ar, articular; an, angular; cp, coronoid process; d, dentary; par, prearticular; sa, sur- 
angular; Meg, Meckel’s groove. About one-fifth natural size. 
The angular is a long, narrow, and thin bone that is closely applied 
internally to the surangular and dentary, and superiorly with the pre- 
articular. Its posterior end is pointed and falls considerably short of 
reaching the end of the surangular. Its forward elongate extremity is 
missing in this specimen, but judging from the width of the broken end 
and the continuation of the flattened surface on the lower border of Meckel's 
groove, the complete anterior termination would be, as in Edmontosaurus, 
at a point below the mid-length of the dental magazine. 
The articular is imperfect, but enough of this element is present to 
show it to be a thin flattened bone that was vertically intercalated between 
the prearticular and surangular, as shown in Figure 9. The upper border 
is thickened transversely and shallowly concave antero-posteriorly in 
conformity with the contiguous surface of the surangular. Its posterior 
border extends to the extremity of the surangular. 
The surangular is relatively more slender throughout than in the more 
robust Hypacrosaurus altispinus, but otherwise there is a remarkably close 
similarity in shape and method of articulation with the dentary and the 
other bones of the inner side of the ramus. The vertical process articulates 
with the inner posterior side of the coronoid process and has a height over 
all of 136 mm. The upper surface has a shallow cotylus, the principal 
articulation of the quadrate, the remaining part being furnished by the 
much reduced articular. Behind the quadrate articulation the surangular 
