THE SKULL OF PALEORHINUS 139 
exoccipitals. The opisthotics may exist codssified with the exoccipi- 
tals as in other reptiles, but this is not determinable. The bones 
forming the floor are the alisphenoids, which are united in their anterior 
parts only, the basisphertoid and the basioccipital. A small spatu- 
late bone which is attached to the lower margin of the posterior por- 
ols. canal 
i po 
. 
‘Foramen 
ovale 
Fic. 5.—Cranine bones from side. Fic. 6.—Bones of brain case. 
tion of the alisphenoid and thence extends downward and slightly 
posteriorly to unite with the pterygoid, is here considered as the 
epipterygoid. In shape and mode of attach- 
ment it occupies a position intermediate 
between the long slender epipterygoid of 
the lizards and the short, solidly attached 
(so-called) epipterygoid of the modern 
crocodiles. Instead of there being only a 
small foramen between the epipterygoid and 
the cranium, as in the crocodile, a large 
: . k Fic. 7.—Cross-section 
space exists beneath the epipterygoid, more through _rhinencephalic 
like the condition in Amblyrhynchus, for ex- canal. 
ample. It is probable that in life this space 
was still larger than at present, and that it has been reduced by crush- 
ing. Just in front of the epipterygoid is the opening for the III, 
oculo-motor, and VI, abducens, nerves, and behind it is the fenestra 
ovale. The foramen magnum is oval in outline and quite large. 
Its floor is formed by the basioccipital, its walls by the exoccipitals, 
and the roof by the supraoccipital. The brain-case is continued 
