by S. H. Haughton. 245 
triangular area the basisphenoid is continued as a narrow vertical 
plate whose lower surface passes forwards and upwards. Near the 
bottom, either side of this plate has a groove, which is separated from 
its neighbour by a free-ending short tongue of the basisphenoid. Each 
groove leads forward into the interpterygoid vacuity whose hinder 
margin is formed by the basisphenoid. In cross-section the basi- 
sphenoid is seen to lie above the interpterygoid vacuity and anterior to 
the vacuity the bone is again seen as a tongue lying between the 
pterygoids at the top of the arch whose side-walls are pterygoidal. 
The side-walls of the interpterygoid vacuity are formed by the 
pterygoids which pass back to lie outside the basisphenoid. The latter 
has a very short basipterygoid process which meets the pterygoid and 
is separated by a thin splint of that bone from the large epipterygoid. 
In front of the anterior tongue of basisphenoid the pterygoids are 
in contact with one another. Here for a short distance there is a 
median groove, but at the level of the transverse processes of the 
pterygoids the palate becomes suddenly vaulted ; and no development 
has been done anterior to this point. 
The side-wall of the brain-case is similar to that of Cynosuchus and 
Diademodon. ‘The sinus canal separates the epipterygoid and _prootic 
from the parietal and passes back to the post-temporal opening. The 
foramen for the exit of branches 2 and 3 of the Vth nerve lies in the 
suture between the prootic and epipterygoid, the former forming only 
its posterior border. The epipterygoid has a suture with, and lies 
external to, the pterygoid anteriorly ; but the pterygoid dies out post- 
eriorly whilst the epipterygoid passes back to meet the quadrate. 
The quadrate is small and fixes on to the squamosal by means of two 
processes which fit loosely into two deep grooves on the under surface 
of the squamosal as in Diademodon. The external auditory meatus 
lies just mesial to the inner of these two grooves. It is deep, but does 
not pass on to the top of the skull. 
The lower jaw is typically Cynodont in structure, with a long 
shallow dentary provided with a large coronoid process, and a 
small postdentary portion. The notch in the lower border of the 
angular is almost covered by the dentary ; and the outer face 
of the bone is provided with a channel facing backwards and 
downwards and passing upwards and backwards from the notch, 
its outer wall formed by a reflected lamina of the angular. The 
splenial meets its neighbour at the symphysis, lying along the inside 
of the dentary. 
In general features this skull is a Cynodont ; but in the possession 
of an interpterygoid vacuity it differs from all the hitherto-described 
