the Skull of Diademodon. 



an 



of such interest tliat^ although almost certainly a Thcro- 

 cephalian and not a Cj^nodont, it is described here. 



The evidence for its Therocephalian nature is of two 

 kinds : — 



1st. The locality is said by Broom to he iu rocks of 

 Permian age. 



2nd. The size of the nou-dentary elements of the lower 

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

 more primitive than any known Cynodont. 



It is probably the most instructive Therocephalian 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. 



Prof. Seeley's description is quite accurate, but some 

 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. 



Fig. 9. — " T/ic7'o}nu!>.'' 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 no doubt the foramen 

 jugulare. Lyiugjust 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 Sphenodon. 



