15 
This flange springs from a stout base extending from the pterygoid processes 
to below the foramen ovale. The outline of the base of the flange is 
lenticular in cross-section, with the length of the lens nearly equal to five 
times its breadth. 
Placed well forward beneath the base of the flange is the external 
opening of a long, straight passage, directed upward, forward, and inward, 
and entering the pituitary space from below, for the transmission of the 
internal carotid artery. Above the flange, about midway between the 
anterior end of its base and the common exit for the third and fourth 
nerves, is a foramen for a branch of the carotid artery opening directly 
into the main passage. This upper opening is small and occurs within a 
concavity of considerable size (about 15 mm. in diameter) in the external 
surface of the bone. Skirting the base of the flange infero-posteriorly is 
a well-defined groove for the course of the artery to its entry beneath the 
flange. 
The upper surface of the basisphenoid posteriorly forms the anterior 
portion of the floor of the medulla oblongata. It is here perforated by 
the forwardly directed passages of the sixth nerves which enter the infundi- 
bulum, one on either side of the midline, from behind. Extending down 
into the great thickness of the bone, in continuation of the infundibulum, 
is the space for the pituitary body about in line with the hinder slope of 
the transverse ridge connecting the pterygoid processes interiorly. 
Measurements of Basisphenoid of Edmontosaurus, Specimen Cat. No. 2289. 
Mm. 
Infero-posterior breadth 110 
Inferior breadth behind pterygoid processes 63 
Breadth across pterygoid processes 186 
Inf ero-anterior breadth 20 
Thickness (depth) at midline, between origin of sixth nerves and infundibuhim, 
to lower surface behind transverse ridge 66 
Thickness (depth) from lower end of pituitary space to lower surface behind trans- 
verse ridge 37 
Superior breadth below optic foramen 18 
Parasphenoid (Pasp.). Figures 3, 5, 7, and 26. In Edmontosaurus 
this membrane bone is beneath the presphenoid as a forward extension 
from the basisphenoid with which it was evidently coalesced. It is 
slender, higher than broad posteriorly, and is spout-shaped in advance 
of the line of the olfactory nerve exit. Leading back from the spout, 
toward the basisphenoid, is a passage about 18 mm. high and 8 mm. 
wide, mostly through the parasphenoid but within the presphenoid to 
about one-third of its height. Whether this passage reaches the basi- 
sphenoid has not been ascertained. The suture between the parasphenoid 
and the presphenoid is indicated externally on both sides by a line of 
demarcation running forward below the level of, and nearly parallel with, 
the floor of the olfactory lobes. 
Alisphenoid (Als.). Figures 4, 5, 7, 8, and 26. The alisphenoid is, 
in its characteristic position in the reptilian skull, in advance of the prootic, 
bounding the large foramen for the trigeminal nerve in front. It forms 
the sidewall of the brain-cavity above the hinder portion of the basi- 
phenoid. It connects postero-superiorly with the parietal, superiorly 
with the frontal, and externo-superiorly with the postfrontal. Interiorly, 
8429—21 
