94 MEMOIRS OF THE CARNEGIE MUSEUM 
of the arched roof of the upper dental groove. Medially the palatal portion is 
developed as a long narrow vertical plate that extends downward meeting the same 
plate of the opposite side mesially for a vertical distance of 12 mm. These narrow 
alveolar plates posteriorly are separated by the intervention of the anterior extremi- 
ties of the vomers and pterygoids, which eventually disappear under the premaxille. 
Basisphenoid (b.s.). — In so far as I can ascertain, owing to the damaged condi- 
tion of this region, the basisphenoid is a heavy subquadrate bone. Posteriorly it 
articulates with the basioccipital by a deep vertical suture; laterally it is over- 
lapped by the interior processes of the pterygoids; anteriorly the long slender pre- 
sphenoid is given off. The suture between these bones is not shown nor have I 
observed it in any of the skulls of Ichthyosawrus that are figured. The length of the 
basisphenoid in specimen No. 603 is about 70 mm. 
Presphenoid (prs.). —The presphenoid appears as a median anterior prolongation 
of the basisphenoid. This long trihedral bar gradually tapers to a point as it 
extends forward. The anterior extremity in No. 603 disappears under the dis- 
placed pterygoids. This bone divides the long interpterygoid vacuity into two 
parts posteriorly. 
Pterygoid (pt.).—The pterygoid is an irregular elongate bone the most con- 
spicuous element of the palatal region. The internal border posteriorly is concave 
antero-posteriorly and forms the lateral boundary of the interpterygoid vacuity. 
Posteriorly the inner margin is beveled off to a thin edge which laps over the lateral 
inferior surfaces of the basisphenoid, and the truncated posterior interior angle prob- 
ably reached and overlapped the anterior portion of the basioccipital. The posterior 
end curves slightly upward where the superior surface meets the inferior lateral 
border of the stapes. Seen from below the posterior border is slightly emarginate, 
the lateral border posteriorly being deeply excavated. Between this excavation 
and posterior emargination the pterygoid develops a process that extends outward 
and downward and laps along the inner inferior one fourth of the quadrate. Ante- 
rior to this lateral notch the bone again expands, the lateral extent of which is hidden 
by the posterior portions of the lower mandible. More anteriorly this element is 
again excavated by a suture that extends inward and forward, and it is by this 
suture that the palatines (of modern nomenclature, transverse bones of Seeley and 
Frass, the ectopterygoid of Owen), are united with the pterygoids. From this point 
the latter extend forward and inward, meeting medially, the anterior tapering 
extremities finally disappearing under and between the vomers. The surfaces of 
the pterygoids are smooth, both of which dip at a slight angle toward the center of 
the palate. 
