AND CLASSIFICATION OF THE FOSSIL REPTILIA. 
195 
The sclerotic circle .—Below the orbit a structure exists which closely resembles the 
sclerotic armature of a Bird (Plate 15), which, when complete, may have approached a 
diameter of 2 centims. A circle of this size might have been contained in the orbit. 
It is inflated in the middle part, in the centre of which appears to be a smooth space of 
matrix ; externally its border is concave. It appears to be formed of radiating thin 
plates in close contact; but the state of preservation does not admit of detailed 
description or absolute identification, for the mass may possibly be dermal armour. 
The hones of the palate. — The bones of the palate are scattered. Their identifica¬ 
tion rests upon, first, the forms of the bones; secondly, their consecutive positions; 
and thirdly, the fact that the vomer, palatine, and pterygoid all carry minute teeth; 
while there can be no suspicion that these elements belong to the lower jaw, since 
the lower jaw is preserved. 
Vomer .—Both vomerine bones are indicated, and both are partly imbedded in the 
matrix. They were very slender, 3 centims. long, and about 2 millims. wide where 
widest proximally. They carried minute teeth, densely placed along the margin. 
The crowns are enamelled, enlarged and pointed, with lanceolate form. 
Palatine hone .—The palatine bone is a long triangle, notched out on the inner 
anterior margin for the reception of the vomer. The bone is 3 '2 centims. long, and 
8 millims. wide posteriorly, tapering away in front. The external border is straight. 
The posterior border is straight and truncated, but rounds into the inner side, which 
is depressed where it received the anterior limb of the pterygoid. The surface of 
the bone is rather convex till it becomes channelled with the groove which leads 
forward to the notch for the vomer. The vomer probably extended along much of its 
inner margin (fig. 1, p. 19). Along the external margin of the palatine bone a row of 
teeth extended. They were rather larger than those on the vomer, though only one 
or two are preserved. 
The pterygoid hone .—The outline of the pterygoid bone is not easily traced. The 
bone is in accidental contact with the palatine bone, and probably in natural union 
with the quadrate bone. It is stronger than the palatine bone, short and broad 
posteriorly, sending a long sharp process forward which I regard as extending interior 
to the palatine bone (fig. 1, p. 19). This process or bone is l'G centim. long, 3 millims. 
wide at the base, and tapers to a point. It carries a few minute teeth, some of which 
appear to be barbed. The interpretation of the posterior part of the bone is more 
difficult, because the bone originally extended in more than one plane ; and it is 
impossible to determine with certainty whether the expanded transversely oblong 
plate which is in contact with the quadrate bone is in natural union. I assume the 
connection to indicate the true relation of the bone. Then it follows that the oblone: 
truncated expansion of the bone which is at present in contact with the palatine 
must be internal, and either have articulated with the basi-sphenoid, as in Lizards and 
Anomodonts, or else with the corresponding surface of the other pterygoid bone, as in 
Dinosaurs. Then there would be no lateral plate for the internal pterygoid muscle 
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