172 
PROF. D. M. S. AVATSON AND MK. E. L. GILL ON THE 
and he shows the parasphenoid with it's cranial face turned to (he mouth. 
The cranial and buccal faces of the parasphenoid had been correctly identified 
by Miali (1881, fig. 3). 
The way in which the pterj'goids actually fitted on to the parasplienoid is 
perfectly shown by two specimens in the Royal Scottish Museum (Nos. 1902. 
73 and 1894.168.2). These actually belong to an early form of Ctenodus 
(the form to which Traquair applied Barkas's name Ctenodus interrirptus) ; 
but as this form had the palate of a Sagenodus,s,nA as the differences between 
typical palates of the two genera are in any case slight, it is appropriate to 
refer to them here. The more perfect of tlie two specimens is depicted, 
from a rough sketch, in fig. 24, p. 193. It shows that the lateral corners 
of the parasphenoid 1 izenge, looked at from the buccal aspect, overlay the 
edges of the pterygoid, but that towards the front of the lozenge these edges 
passed on to its buccal face and met each other across it by a square corner 
.at the hinder end of their symphysis. Well-preserved examples of the 
Fig. 7. 
Sagenodus. Snb-operculum, x f . A, outer surface ; B, inner surface of another example, 
pterygoid (fig. 8, A, p. 173), as a matter of fact, always show a roughened 
surface corresponding to the corner of the parasphenoid to which they were 
articulated. (It is of the same character as the corresponding narrower 
surface on the pterygoids of Ceratodus, and has been figured b}^ Atthey and 
by Williston.) They also show the corner at the hinder end of the symphysis 
by which they met their fellow across the face of the parasphenoid, and the 
imprint of these corners is occasionally visible on a detached parasphenoid. 
It is only in " Ctenodus interruptus " that the corner is square. In other 
forms both of Ctenodus and Sagenodus it is obtuse and meets its fellow in a 
forvvardly-pointing angle. The arrangement of the elements of the palate in 
a typical Sagenodus in seen in fig. 10, p. 176. 
The meeting of the pterygoids across the front of the parasphenoid may 
in part explain the singularly weak pterygoid symphysis. In Ceratodus the 
pterygoid symphysis is very much stronger th.m that of the lower jaw ; in 
Sagenodus it is altogether weaker, for the bones meet only in a long, thin 
