16 
fusion with the basisphenoid probably took place as the suture here is 
not seen, also its anterior boundary is not distinguishable and its coalescence 
with the orbitosphenoid in front may, therefore, have been complete. 
The division between the alisphenoid and the prootic is marked by a 
suture which descends from the floor of the supratemporal fossa and enters 
the foramen for the trigeminal nerve from behind in the upper curve of 
that opening. The parieto-alisphenoid suture runs forward, from the 
upper end of the prootic suture, with a slight inclination upward, and 
curving outward reaches the postfrontal in advance of and below the 
anterior border of the supratemporal fossa. 
In advance of and above the foramen ovale a stout ridge is developed 
which running upward and outward forms an inferior angulation of the 
bone between the supratemporal fossa and the orbital cavity. This ridge 
in its upper part constitutes a buttress which reaches the postfrontal at 
the upper, inner margin of the opening of the spacious postfrontal pocket. 
The inner portion of this upper prolongation of the alisphenoid meets the 
frontal from below entering into the formation of the sidewall of the 
brain-cavity at the posterior part of the cerebrum. In advance of the 
lower end of the angulation of the alisphenoid the cranium is suddenly 
much compressed laterally and in the hinder part of the depression of the 
external surface thus formed which continues upward the anterior lateral 
compression of the basisphenoid above the pterygoid processes, is the 
foramen for the transmission of the third and fourth nerves about 25 mm. 
in front of the foramen ovale. 
The foramen ovale deeply notches the hinder border of the alisphenoid. 
The outer opening of this foramen is contracted in front, and from it a 
narrow groove extends forward on the external surface of the bone for the 
accommodation of the ophthalmic branch of the flfth nerve. This is 
much the same as in Iguanodon (Hulke, 1871, p. 203, pi. XI, and Andrews, 
1897, p. 588, text fig.). The groove is present in a fragmentary cranium 
of “ Trachodon ” sp., from the Edmonton formation of Alberta, described 
and figured by Brown in 1914 (p. 547, pis. XXXVI and XXXVII). In 
Triceratops this branch of the nerve passed forward deeply embedded in 
bone and found exit at some distance in advance of the common opening 
for the maxillary and mandibular branches. 
Orbitosphenoid (Orsp.) and Presphenoid (Psp.). Figures 5, 7, and 26. 
As alread}' stated the anterior limit of the alisphenoid has not been deter- 
mined, but extending forward from this element is an extensive surface 
between the basisphenoid and the parasphenoid below, and the frontal 
above. The hinder part of this surface is apparently the orbitosphenoid, 
and the forward part the presphenoid, but no sutures can be detected 
defining their boundaries except above and below where well-marked 
sutural lines are preserved. 
In cranial material at present thought to be referable to Stephanosaurus 
the suture between the alisphenoid and the orbitosphenoid is clearlj^ 
indicated extending from the foramina for the third and fourth nerves (in 
Edmontosaurus a single opening) upward, in advance of the buttress of 
the alisphenoid, to the frontal. Hay has found that in Triceratops the 
foramen for the third nerve and possibly the fourth lies in the boundary 
between the orbitosphenoid and the alisphenoid bones (Hay, 1909, p. 102). 
’ t is probable that in Edmontosaurus also the course of the boundary of 
