GILMORE : OSTEOLOGY OF BAPTANODON (MARSH) 97 
face of the posterior end of the ramus in Baptanodon is composed of the angular and 
surangular, the former contributing the greater share. In most of the Ichthyosaurs 
the latter element contributes the greater part. 
Angular (ag.). — The angular is a long curved bone that forms the lower posterior 
boundary of the jaw. The anterior end tapers to a point similar to the surangular 
and disappears between the splenial and dentary just in advance of the anterior end 
of the surangular. (See Pl. VIII.) The suture between this bone and the splenial 
posteriorly passes to the inner side. The angular then underlaps the splenial and 
Fic. 3.. Internal view of the posterior end of the left mandibular ramus of Baptanodon discus (No. 603). One 
half natural size. art., articular ; ag., angular ; cor., coranoid (?) ; s.ag., surangular ; s.q., articulating surface for the 
quadrate. 
coranoid (?) and more posteriorly develops an inner plate that encloses the lower 
part of the articular. 
Articular (art.). —The articular apparently is the least understood of any of the 
elements composing the Ichthyosaurian jaw. Of all the literature to which I have 
had access I have yet to find an adequate description of this bone. Fortunately the 
mandible pertaining to specimen No. 878 has both of these elements preserved in 
situ, while the right articular of No. 603 was found nearly in position but has been 
detached for purposes of study. It is this element upon which this detailed descrip- 
tion is based. 
As in most reptiles the articular is placed far back in the ramus. In Baptanodon 
it is held in position by the enclosing walls of the angular, surangular and cora- 
noid (?). The angular entirely encloses the lower portion curving up on the inner 
side, developing even more of an inner portion than is found in the Crocodile. 
Viewed superiorly the articular is a short solid subrectangular bone (see figs. 4 and 
5.) The upper surface is smooth and gently convex transversely, quite flat antero- 
posteriorly with the exception of an elevated transverse ridge at either end. Poste- 
riorly the end is subtriangular in form the longer side looking downward and out- 
ward. ‘This end is somewhat convex from above downward, presenting a slightly 
