13 
midline, is the supra-occipito-paroccipital arch. Between the parietal and 
inner part of the squamosals and the hinder border of the supra-occipital, 
the space, representing apparently a confluence of the posttemporal 
fenestrse occasioned by the very limited entry of the parietal into the 
occiput, extends forward for at least 50 mm., beyond which it has not been 
possible to follow it. Issuing from either side of the space is a well-defined 
groove (Figure 6, d) in the squamosal which ascends outward to the upper 
surface of the bone and there disappears. Between the squamosal and 
the supra-occipital, and below the groove is what appears to be a foraminal 
opening (Figure 6, e). 
Basisphenoid (Bs.), Figures 5, 6, 7, and 26. This element, preceding 
the basi-occipital in the basicranial axis, and constituting the inferior 
member of the parietal segment of the cranium, is a robust bone of dis- 
tinctive shape. It is in contact behind with the basi-occipital, above 
with the alisphenoids and orbitosphenoids, and presumably supero-pos- 
teriorly with the prootics also, but except in front where it runs beneath 
the orbitosphenoids its upper boundaries cannot be made out in the material 
available. Anteriorly it extends forward, without trace of suture, as the 
parasphenoid. 
In inferior aspect this bone is broad posteriorly, contracts forward, 
and then throws off to either side, from slightly in advance of what is 
considered to be its midlength, a stout process which is directed outward 
and slightly downward to connect with the upper border of the pterygoid 
between that bone’s alar extensions. In front of the processes the bone 
narrows rapidly to the breadth of the slender parasphenoid. The outline 
of the bone, as seen from below, may be said to be irregularly star-shaped 
with five rays composed of the anterior constriction, the lateral pterygoid 
processes, and the postero-lateral angles, the rays represented by the 
processes being longer than the others. 
The lower surface of the basisphenoid is crossed at about its midlength 
by a strong transverse ridge connecting the two processes infero-posteriorly. 
Behind this ridge the lower surface of the bone lies in the general plane 
of the basi-occipital, is transversely concave, and postero-laterally is 
rugosely tumid next to and supplementing the basi-occipital tubercles. 
The posterior slope of the transverse ridge faces backward and very slightly 
downward. In advance of the ridge the surface of the bone between 
the processes is widely concave in all directions, and is inclined strongly 
upward so as to face obliquely forward and downward, much as in Iguan- 
odon. Medially on the ridge a small, tongue-shaped process is developed 
which points downward with a slight backward curve. 
The pterygoid processes are flattened above and below, are thickest 
behind, and narrow to the front, the cross-section at the base being triangular 
with the apex of the triangle directed forward, and the sides lengthened. 
They terminate bluntly. Covering their thick, obtuse ends and extending 
inward with decreasing breadth for a distance of over 60 mm., on their 
front faces is a roughened surface denoting contact with the pterygoid. 
Between this articular surface and the parasphenoid the bone comes to a 
sharp edge. 
Supero-laterally, above its contraction behind the processes for the 
pterygoid, it sends outward a thin, triangular, wedge-shaped fiange, set 
at an angle to the horizontal so that its upper face is inclined forward, 
8329—2 
