17 
the alisphenoid lay from this particular nerve opening up in front of its 
angulated buttress. The area in advance of the alisphenoid, regarded as 
the orbitosphenoid, connects superiorly with the frontal and inferiorly 
with the basisphenoid. The presphenoid in front forms the floor beneath 
the olfactory lobes and may include that part of the area from the opening 
for the optic nerve to that for the first or olfactory nerves, and upward to 
the frontal, but the proportionate extent of the contact of the presphenoid 
and orbitosphenoid with the frontal is not known. Apparently the inferior 
connexion of the presphenoid with the basisphenoid and parasphenoid is 
extensive, limiting that of the orbitosphenoid with the basisphenoid. The 
presphenoid in its extension upward to the frontal flanks the olfactory 
lobes and the oriflce for the exit of the olfactory nerves on either side, 
but whether it or the frontal encloses the opening above has not been 
ascertained. 
Prodtic (Prot.). Figures 4, 5, 8, and 26. This cranial element is behind 
the alisphenoid and in front of the epiotic and opisthotic, neither of which 
latter, however, are distinguishable as distinct bones in the Edmontosaurus 
skull,- both, following the usual rule of cranial development in reptiles, 
having probably early fused, the epiotic with the supra-occipital and the 
opisthotic with the exoccipital. Superiorly this bone reaches the parietal, 
and inferiorly the basi-occipital, and possibly also the basisphenoid to a 
limited extent. 
The prootic is pierced by the foramen for the seventh or facial nerve 
(VII). In front it completes the opening for the trigeminal nerve behind, 
and its hinder border is deeply notched by the fenestra ovalis (?+ the 
fenestra rotunda). 
In Edmontosaurus (specimen. Cat. No. 2289) the suture between the 
prootic and the alisphenoid is shown in its upper course. It is seen to 
leave the foramen ovale high up in the posterior margin of the opening 
and to ascend, first for a short distance slightly forward, and then for a 
greater distance backward, to the parietal above. It is clear, therefore, 
from the position of the suture, that the greater part of the opening 
is in the alisphenoid as it is in the alligator. In the Jurassic herbivore 
Camptosaurus (Gilmore, 1909, p. 210, fig. 5) the foramen ovale is mostly 
in the prootic, as it is also apparently in Triceratops. Hay in his paper 
of 1909 on the skull and brain of Triceratops remarked that ‘fin Triceratops 
the suture between the prootic and the alisphenoid may be provisionally 
drawn through the front of the foramen” (foramen ovale). 
Superiorly the prootic extends outward from the parietal as part 
of the floor of the supratemporal fossa. At the outer edge of the floor 
it is angulated horizontally and overhangs the lower portion of the bone 
which is concave externally in a vertical direction down to the basisphenoid. 
This upper angulation or ridge, originating from the prootic, extends 
horizontally backward, parallel to a similar ridge developed in the opistho- 
tic, and merges posteriorly in the upper face of the paroccipital process 
of the exoccipital. Between the two ridges the external surface is vertically 
concave and in this concavity the suture marking the antero-superior 
boundary of the opisthotic is to be looked for leading upward and backward 
from the fenestra ovalis. This suture is shown in this position in a cranium 
of ‘‘Trachodon” sp. figured by Osborn in 1912 (p. 18, fig. 13, Amer. Mus. 
No. 427). 
