58 . FIELD CoLUMBIAN MusEuM—GEOLOGY, Vor. II. 
is slender. The two bones meet in a median suture on the under 
side of the sphenoid, their posterior border forming a wide and deep 
concavity. The outer margin of the bones converge from the quad- 
rates as far forward.as the posterior end of the interpterygoid vacui- 
ties, where they curve outward into the posterior border of the ecto- 
pterygoid processes. The under surface is shallowly concave on 
either side back of the vacuities, but in the middle there is a rather 
strong, obtuse ridge. A little back of the vacuities, on either side, 
with their origins separated, a narrow and strong ridge arises to 
curve outward and become lost on the under border of the somewhat 
descending ectopterygoid process. In front of the vacuities the two 
bones again meet in a long median suture. The palatal surface here 
occupies a somewhat higher plane than that of the posterior part, and 
is flat throughout. The bones of the two sides gradually narrow in 
width to terminate by an obtuse extremity near the middle of the 
palate. Between the ectopterygoid processes and between the curved 
ridges already described there is a narrow, deep vacuity, with two 
oval, elongated, well-defined foramina or vacuities at the bottom, the 
‘‘palatonares” of Owen, the ‘‘posterior palatine vacuities” of 
Andrews, the ‘‘interpterygoid vacuities” of authors. A  discus- 
sion of their character will find a place further on. The lateral walls 
of this fossa posteriorly are nearly vertical, but the anterior end of 
the fossa is but little or not at all excavated above the plane of the 
palate here. From the anterior end of the median posterior :nter- 
pterygoid suture two sutures diverge, leaving a large angular sloping 
surface exposed which forms the posterior roof of the fossa; the bone 
exposed between the V-shaped sutures is the basisphenoid, and has 
attached to it by suture the so-called parasphenoid bone in front. 
Just how the diverging sutures terminate I cannot definitely say. 
They seem to follow the lower angle of the lateral wall of the fossa 
as far forward as the middle of the vacuities and thence return to join 
the parasphenoid suture at the posterior part of the vacuities. If 
this determination is correct, these projections would correspond to 
the basipterygoid processes of the lizards. The ectopterygoid pro- 
cesses ot the pterygoids, the continuation of the curved ridges, have a 
rounded, prominent under border, with a terminal, large, vertical or 
oblique, abutting, mandibular surface. This ridge and its abutting 
surface are very much as they are in Plosaurus, and the whole struc- 
ture here also reminds one of the crocodiles. 
The transverse, transpalatine or ectopterygotd bone is a rather 
small, flattened polygonal bone, whose under surface is continuous 
with that of the palatine and pterygoid in front. It joins the ptery- 
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