752 MR. D. M. S. WATSON ON 
fifteen centimetres of solid finely cancellar bone may be formed 
over the brain. The bones of the face, although they may be two 
centimetres thick, never fuse, and were readily disarticulated in 
the adult skull. 
Text-figure 2. 
IL [Pain 
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Pep Ex: 
Mormosaurus seeleyi. Dorsal aspect of the type-skull, X 7. 
Reference-letters as before, with :—Fr., Frontal; I.Par., Interparietal ; 
Par., Parietal. 
The whole occipital and otic region of the skull (text-figs. 3, 7) 
has fused into a mass of bone in which no sutures are visible in 
the material at my disposal. On the whole this region is very like 
the corresponding part of Lystrosawrus which I have already 
described. It forms a thick, vertically placed plate of bone 
pierced through the middle by the relatively small brain-cavity. 
This is throughout higher than wide, and has not been cleaned in 
any specimens; fractures, however, show that it possessed the 
characteristic Therapsid character of having the large opening to 
the vestibule placed very low down in the skull. The floor of 
the brain-cavity rises considerably towards the front. 
The basioccipital condyle (text-figs. 5, 4, 7) is single, large, and 
slightly pedunculate (R. 3596); it has a slight median depression 
representing the notochordal pit. Below the condyle, the basi- 
