AND CLASSIFICATION OF THE FOSSIL REPTILIA. 
2.31, 
wide. They diverge but little posteriorly, and on tlie inner side appear to show well 
defined sutures separating’ them from the bone beneath, which would necessarily be 
the inter-parietal. The bones diverge anteriorly to disclose the parietal foramen, and 
appear to show the parietal in front of them, as they open in a V shape. I regard 
the lateral suture as following the divarication anteriorly round the impressed 
muscular area to the post-frontal bone. In the genus indicated by Dicynodon 
tiyriceps their development is different, because the roof of the skull is flat. They 
are narrow concave strips of bone which extend round the margins of the temporal 
vacuities, so as to display the parietal bones between them. 
These bones seem to me to be called into existence by the muscular attachment, 
and they may correspond to the parietals of higher Vertebrates, where the single 
rieptilian parietal probably becomes absorbed. 
Turning to the base of the specimen H. 86H, the basi-occipital and basi-sphenoid 
are seen to be anchylosed together. The union is marked by a transverse ridge, 
behind which the basi-occipital extends for Iff centim. The combined bones are 
produced downward and outward into two strong processes, divided by a longitudinal 
median channel. The extremity of each process forms a large concave articular facet, 
which looks outward and downward, and is somewhat heart-shaped, and about 
I'D centim. wide. I regard this surface as having given attachment to a bone, the 
mastoid, which extended transversely outward to the squamosal and quadrate, as in 
D. Ictcerticeps and other specimens. .A large hemispherical cavity which is opposite 
to it in the squamosal bone, is 2 centims. wide, and looks forward and downward, may 
have given partial attachment to its other end. The distance between these surfaces 
for the malleus is about 4’5 centims. 
The squamosal bone is a large vertical plate, which forms the whole of the lateral 
expansion of the back of the head, external to the occipital plate (fig. 1). It is 6 centims. 
wide on the anterior aspect, and 5 centims. wide in the middle, posteriorly. It is 
8 centims. high. The bone becomes compressed as it extends downward and outward, 
so as to form a support for the quadrate bone, which was placed in front of its distal 
end, as in D. leoniceps and other species, though the bone is lost from this example, 
as in D. ]jardiceps, D. tigriceps, and other species. An impressed surface which 
received it is but slightly indented, so that the attachment was loose and squamous. 
The main portion of the squamosal bone extends the plane of the ex-occipital outward, 
and its external border descends in a curve which is at first concave and then convex, 
so that the bone widens as it extends distally. Superiorly it sends a few sutural 
processes inward over the ex-occipital, and it extends in front of that bone anteriorly. 
Its transverse superior contour is concave. From the outer upper angle a greatly 
compressed and oblique bar is given off’, which extends forward to form the external 
border of the temporal foss, though it is fractured (fig. 2), and tlie foss is not defined 
in this specimen. 
It may be worth recording that the thickness of the occipital plate suddenlv 
