t It e Shdl of Diademodon. 315 



inner edge of the post-temporal fossa, which is rehitivcly 

 l)igi5;er than in Diademodon, passes straight inwards, about 

 halfway to the foramen magnum and then tnrns vertically : 

 it ri^es well above the foramen magnum and is tlien lost. 

 This suture separates the parietal from the exoccipital, 

 snpraoccipital, and interparietal. 



The paroccipital processes are powerful and their anterior 

 faces are weathered, away so as to show the strneture. 

 Slight differences in this structure and on the left side an 

 apparent suture suggest that each process is composed of 

 two parts, an upper and smaller, which is probably the 

 exoccipital, and a lower the opisthotic. 



The bone forming the upper part of the post-temporal 

 fossa is the parietal, and the suture which separates it from 

 the pro-otic part of the periotic is plainly visible on both 

 sides. 



Along the suture runs a deep groove, and a broken area 

 along the top of the pro-otic shows that this was formerly 

 covered by a lamina, just as in Diademodon. In the suture 

 is a small foramen opening outwards and backwards. The 

 broken edge on the pro-otic is continued outwards and 

 downwards so as to show that there was formerly a strong 

 lamina covering the groove leading from the pterygo- 

 paroccipital foramen to the post-temporal fossa. 



The pro-otic bears a comparatively small process for 

 articulatiou with the pterygoid. 



The deep pit lying just external to and in front of the 

 condyle is very large and well shown ; it has apparently 

 four foramina opening into it : — 



1. A small foramen passing directly backwards just above 

 the condyle. 



2. A large foramen opening into the very bottom of the 

 pit. 



3. A small foramen opening forward. 



4. A small foramen opening inwards. 



Immediately to the outside and slightly in fix)nt of the 

 j)it is the fenestra vestibuli, an oval hole about five milli- 

 metres across. Except on the side towards the pit the 

 fenestra is surrounded by a wide flat area. 



Slightly in advance of the fenestra vestibuli lies the small 

 oval foramen for the facial nerve ; and from it a narrow 

 groove, presumably a suture, passes upwards and forwards 

 to cut the upper surface of the basisphenoid above the 

 posterior rim of the pituitary fossa. This suture separates 

 the pro-otic region of the periotic from the basisphenoid. 



On the front end of the specimen the posterior face of the 



