tlie Skidl of Diadcmodon. '.]] 7 



of such interest that, although almost certainly a Thcro- 

 ccphalian .nnd not a Cvnodont, it is described here. 



The evidence tV)r its Theroccphaliau nature is of two 

 kinds : — 



1st. 'I he locality is said i)y Broom to be in rocks of 

 Permian age. 



'2ih\. The size of the nou-dentary elements of the lower 

 jaw and many other details of its structure show that it is 

 more j)rimitivc than any known Cynodout, 



It is i)robably the most instructive Therocephaliau skull 

 known, although it is only represented by an impression in 

 liard sandstone, and the structure is only intelligible in 

 artificial impressions taken from it. 



I'rof. Seeley's description is quite accurate, but sonie 

 further details may be made out. 



The bones of the basis cranii are seen from above (fig. 9). 



The occipital condyle is not well shown and its left side 

 has been destroyed ; it seems, however, to have been at least 

 incipiently double. 



JIM. 



Fig. 9. — " Tho'omun.'' Dorsal surface of the bones of the basis cranii 

 and palate. Car., foramen for internal carotid ; Int.ear., opening to 

 internal ear 



Just in front of it is a small foramen, probably for the 

 ]2th nerve. 



In front of this again is a much larger foramen leading 

 outwards and backwards ; this is lao doubt the foramen 

 jugulare. Lying just in front of the foramen jugulare on 

 on each side is the great opening leading into the inner ear. 



This opening, which was of course closed by a membrane 

 during life, is relatively larger than in any recent reptile 

 except Sjjhenodun. 



