GILMORE: OSTEOLOGY OF BAPTANODON (MARSH) 91 
lateral extremities narrowing somewhat as they descend to oceupy the space between 
the internal branch of the squamosal and the supraoccipital. 
Frontals (fr.).— The frontals are, so far one may rely on the very unsatisfactory 
evidence at hand, very small and in a general way resemble those elements observed 
in the skulls of the Ichthyosawria generally. The sutures of this region are quite 
indistinct being indicated by hardly more than fractures. These fractures however 
having been produced by pressure would naturally have followed the line of least 
resistance, which in this case is that of the sutural union of the different elements. 
As these fractures have the position and direction of the sutures shown in the draw- 
ings of Ichthyosaurian skulls I haye had them drawn in provisionally. See Plates 
VIII. and IX. Because of the conjectural nature of the above evidence no attempt 
will be made to describe this region in detail. This portion of the skull of No. 603 
is so badly crushed that all sutures have been entirely obliterated. 
Postfrontal (ptf.).— The posterior border of this bone is well shown, but anteriorly 
as explained above the sutures are only indicated by transverse fractures. The 
post- and prefrontals will be considered here as a single element extending from the 
supratemporal behind to the rounded fracture forward where it unites with the elon- 
gated nasals. Although in Ichthyosaurus Frass shows a suture immediately over 
the eye separating the pre- from the postfrontal, there are no indications of such 
a suture in our specimens. Reynolds* says “The exact position of the suture be- 
tween the prefrontal and postfrontal is not known.” ‘This element as here considered 
isa moderately long compressed bone forming the quite horizontal postorbital arch. 
Posteriorly the bone is obliquely inclined so that the outer surface looks outward 
and upward. Fore and aft the element is convex. The nearly square posterior 
end unites with the supratemporal, the postero-superior margin with the anterior 
branch of the squamosal, the latter being prolonged on the inner surface of the 
postfrontal which is united by an extended suture. The outer or inferior border at 
this end joins the upper border of the postorbital for about 63 mm., but more an- 
teriorly this bone alone forms the upper boundary of the orbit, at this point assum- 
ing a nearly horizontal position. Anteriorly this element acquires its greatest width 
as it curves in front of the temporal fossa to meet the parietal and frontal. Though 
how much of this wide portion if any is prefrontal we cannot determine at this 
time. ‘The superior surface in front of the temporal opening is elevated into a 
rounded transverse ridge which becomes narrower and somewhat depressed as it 
approaches the junction with the parietal. Anterior to this ridge the surface is 
slightly convex transversely and bends downward longitudinally to meet the 
nasals. 
28 Reynolds, ‘‘The Vertebrate Skeleton,’’ p. 196. 
