228 
PROFESSOR H. O. SEELEY ON THE STRUCTURE, ORGAN IZ ATI OX, 
inverted V, descend over the summit of the chamber and give attachment to a hone 
which, if the constituents of the occipital plate are correctly determined, should 
theoretically he the inter-parietal. At the inferior outer angle of the chamber there is 
a bony prominence on each side, which defines a notch like the outlet for a nerve 
which should give attachment to the ali-sphenoid bone. 
A Specimen showing the Relative Height of the Cerebral Chamber. (Plate 10, fig. 3.) 
Similar evidence as to the form of the back part of the cerebral chamber is seen in 
the British Museum specimen 47,056, described in the South African Catalogue, 
No. 80, as Dicynodon leoniceps. It may, perhaps, be another species, for, though it 
resembles that type in the form of the face, the head is relatively shorter, and the 
palatal characters, in so far as exposed, are more like those of Dicynodon pardicep>s. 
In this skull, which is 32 centims. long as preserved, the bones of the occipital plate 
hove been broken away, exposing a natural cast of a portion of the posterior aspect 
of the brain cavity, which is 8 centims. high. The mould is inclined obliquely 
forward, and its straight posterior contour makes an angle of 60^ with the horizontal 
plane of the frontal region produced. The base of the foramen magnum is 2 centims. 
wide, and at about this height from its floor the mould of the cerebral chamber 
expands a little transversely, giving a convexity to the lower part of the side, and it 
contracts superiorly to less than half its width at the summit. The inclined sides 
diverge outward as they extend forward, and, as far as exposed, they are flattened. 
The straight posterior contour is rounded convexly from side to side, like the surface 
of a segment of a cone. In every respect the cerebral characters of this specimen are 
absolutely the same as in the occipital plate just described, only difiering as do a seal 
and an imjrression from it. 
Another Specimen, shoiving part of the Brain-case, and some characters of the Back of 
the Skull. (Plate 11.) 
A specimen in the British Museum, numbered II. 868, apparently indicates a new 
species, distinguished by having the back of the head more than twice as wide as 
high, with the hyp-apophyses close together. The occipital condyle is hemispherical. 
The foramen magnum is less high than the condyle is deep. The so-called par- 
occipital process of the ex-occipital is wider than the rest of the bone. The sides of 
the narrow bones which form the temporal region are inclined to each other and 
parallel, and arch high above the descending plate of the squamosal. The back of the 
head is as wide as in Ptychognathus latirostris, but the form of the temporal region is 
that of Dicynodon leoniceps. It may be termed Dicynodon microtrema. 
The brain-case is crushed a little obliquely downwards. Its base is formed by the 
anch 3 dosed basi-occipital and basi-sphenoid, and the basi-sphenoid is broken trans 
