South African Fossil Reptiles and Amphibia. 205 



border there is a process which projects into the fossa on a level 

 with the floor of the posterior part of the brain-case. At the 

 level of this process the side-face of the bone is provided with 

 a broad shallow horizontal channel 



The epipterygoid is not visible, but Watson has described it 

 as a slender rod rising very high in the skull with its posterior 

 edge nearly in contact with the front of the prootic, arising from 

 a small process of the pterygoid which curves round so as to shield 

 the front of the fenestra ovalis. 



The occipital plate is weathered but the limits of some of the 

 bones can be made out. There is a fairly small supra-occipital 

 forming the upper border of the foramen magnum. The inter- 

 parietal is a larger bone lying above the supra-occipital. The 

 upper portion of its lateral edge articulates with part of the parietal 

 which overlaps on to the side of the occipital plate ; the lower 

 portion with the tabulare. The post-temporal fossa is very small. 



GORGONOPSIA.- In view of the generally accepted belief 

 that the Gorgonopsia are nearly related to the Cynognathidae, 

 and consequently close to the line of mammalian descent, it be- 

 comes important to elucidate as much of their detailed structure 

 as possible. Watson, in a study of the external aspects of the 

 brain-case, has traced a gradual change from Dimetrodon through 

 An-tops and Scymnognatkus to Diademodon, without, of course, 

 suggesting that these genera lie actually on the one line of descent. 

 It has recently been possible to study the interior of the brain- 

 cases in one or two Gorgonopsia, and the results obtained are 

 given here. 



The first skull examined was a large skull the largest Gorgon- 

 opsian skull known to me allied to Scymnognathus tigriceps. It 

 was collected by the Rev. J. H. Whaits at a height of 3,500 feet 

 on Zuurplaats in the Graaff-Reinet district, and is possibly thus 

 from the bottom of the Cistecephalus zone. The interior of the 

 brain-case has been completely cleared. 



Watson in 1914 gave a short description of the brain-cavity 

 of Scymnognathxs whaitsi ? accompanied by a figure of a sagittal 

 section. The specimen showed '' a distinct resemblance to 

 Diademodon owing to the comparatively thin basioccipital and 

 the large opening to the vestibule through the posterior end of 

 which the tenth nerve has its exit. The general features of the 

 vestibule recall Diademodon, but there is no visible trace of a 

 cochlea. The chief differences from the more recent animal are 



