230 
PROFESSOR H. G. SEELEY ON THE STRUCTURE, ORGANIZATION, 
squamosal bone on its external boi’der, and two pairs of bones on its superior border. 
And since ilie sutures in this occipital plate are obliterated between the basi-occipital 
and ex-occipital bones, there is an a 'priori probability that they would be obliterated 
between the ex-occipitals and the supra-occipital, and, therefore, that the composition 
of the occipital plate in R. 868 may have originally been the same as in R. 1021, so 
that the supra-occipital would enter into its foramen magnum. Hence, there is some 
ground for supposing that the pair of distinct bones which surmounts the occipital 
plate is a pair of inter-parietal bones, with an immense antero-posterior extension. 
A pair of bones behind the parietals has been figured by Professor Feitsch^ in many 
genera of Labyrinthodontia, so that they would seem to characterize that order; 
but the small size of his specimens and their flattened condition would be unfavour¬ 
able for the identification of a supi’a-occipital bone below them, if it exists, and these 
bones, if distinct from the supra-occipital, would also be inter-parietal. 
The bone which flanks the inter-parietal in Loxomma is termed by Dr. Embleton, 
mastoid ; and is the e):)i-otic of Dr. Feitsch, though this determination has been 
questioned. 
It is well seen at the side of the skull of R. 868 as a broad plate of bone, which 
extends between the inter-parietal and the squamosal, and rests upon the supra- 
occipital part of the occipital plate, so that in plan of construction of this region of 
the skull there is a close approximation to the Labyrinthodont type, which, in so far 
as I can judge from Mr. Maw’s specimen of Loxomma in the British Museum, has a 
vertical occipital region. 
The transverse extent of this {V) epi-ofic bone is 4 centims. in R. 868 ; its position 
is oblique, and its breadth about 1'5 centim. In other species the position of this 
bone is different; in Dicynodon leoniceps it appears to descend obliquely downward, 
outward, and backward. In Dicynodon tigriceps its development appears to be 
greater upon the roof of the skull, Avhere it seems to me to overlap the parietal bone, 
and to be defined by difference of colour of the bone, and a convex sutural border 
which allovvs the undivided parietal to extend back between the epi-otic bones. 
The epi-otic bones are in contact with the pair of remarkable bones which form the 
roof of the temporal region of the skull. These bones are each about 1‘8 centim. 
Avlde, somewhat inclined towards each other so as to look upward and outward, Avith 
the surface slightly convex from within outward, and the external margin, aaIucIi 
projects well beyond the inter-parietal, is well rounded. The anterior fracture shows 
the thin blade-like substance of the bone. Its sides are sub-parallel, except that 
posteriorly it diverges outAvard and dowiiAvard, so as to rest on each side upon the 
margin of the epi-otic. These bones have usually been regarded as the parietals. But 
they appear probably to be distinct plates, Avhich are developed in the position Avhere 
the muscles which AAnrk the lower jaw are attached. In Dicynodon leoniceps these 
bones, Avhich have a similar smooth oblique surface, are 20 centims. long and 3 centims. 
* ‘ Fauna der Gaskolile nnd der Kalk.steiiie der Peraifovmation Bdliinen.s.’ 
