24G 
PEOFESSOR H. G. SEELEY ON THE STRUCTURE, ORGANIZATION, 
Ornithosaurs extend from the sphenoid to the distal end of the quadrate, and less 
slender than the relatively lonof bones in the Birds skull, which extend from the 
anterior inner angle of the quadrate articulation, and converge forward and inward 
to the sphenoid, which have been regarded as pterygoid bones. Nothing like these 
bones of Anomodonts has been recognized in existing Reptiles ; and they are regarded 
as homologues of the malleus of the Mammalia on account of their relation to the 
surrounding bones. 
Fig. .3. 
Plan of palate of Dicynod,on. 
The cavity which contained the brain is small, narrow, and high. It appears to 
have the basi-occipital and basi-sphenoid for its floor. The pre-sphenoid ascends 
obliquely in front, and is very narrow, and there is no certain evidence whether 
the olfactory nerve was prolonged above it. The superior covering of the brain was 
formed by the supra-occipital, inter-parietal, and parietal bones ; there is no evidence 
that the brain extended forward to the region of the frontal. It has been seen that 
the ex-occipital bones enter into tlie foramen magnum, but on the anterior side the 
occipital plate thickens, and the thickening appears to be due to a bone, which loses 
its individuality at an early period, being super-imposed. I regard this bone as the 
opisth-otic. Its anterior margin is smooth, and formed the hinder wall of a vertical 
aperture in the brain-case through which a large nerve passed. It corresponds to 
the outlet for the fifth nerve, but other nerves also, probably, passed out in the same 
channel. Anteilor to this aperture is a large vertical plate, which rises from the 
basi-sphenoid ; and this I regard as the ali-sphenoid bone. It is very thin, and may 
not always have been ossified, but is well seen in Ptycliognathus. Much further 
forward, above the pre-sphenoid, are the bones which appear to correspond to the 
