MAMMAL-LIKE REPTILES. 



227 



only the general appearance of the palatal elements when viewed 

 from below, our knowledge of the morphological structure has 

 been gained mainly by the skulls of Scymnognatlms tigriceps and 

 Scylacognathtis parvus. The settling beyond question of the 

 nature of the palate, and especially of the vomer, was a matter 

 of such importance that I have not hesitated to break up the 

 skulls of both of these types. As museum specimens they are 

 none the worse for having been broken across in various direc- 

 tions and internally dissected, and, as a result, every detail of the 

 iuterual anatomy is now known. 



For many years I have known that the type of Gorgonops 

 torvus showed an apparently undivided median vomer, but whether 

 it was a true vomer or a pair of prevomers fused as we get in 

 Ornithorhynchu,s it was impossible to tell. In typical Thero- 

 cephalians there are two prevomers as in Lizards and Rhyncho- 

 cephalians. In Anomodonts and Cynodonts there is a single 

 unpaired vomer as in Mammals. A good many years ago (1895) 

 I endeavoured to maintain that the mammalian vomer was not 

 homologous with the reptilian paired vomers, but that these 

 latter were the homologues of the dumb-bell bone of Ornitho- 

 rhynchus. The question has been discussed by Gaupp, Versluys, 

 Fuchs, Osborn, Williston, and others, but may be said to be still 

 unsettled. As the Gorgonopsia stand between the Thero- 

 cephalians on the one hand and the Anomodontia and Oyno- 

 dontia on the other, it is in this suborder that we must look for 

 a solution of the vomer problem. Unfortunately, the skulls 

 examined still fail to give us the solution, as both Scymnognatlms 

 and Scylacognathus agree with the Anomodonts, Cynodonts, and 

 Mammals, and differ from the Theroeephalians in having a 

 median impaired vomer and, so far as can be seen, no trace of 

 paired vomers. 



Scyinnognathus tigriceps (PI. XXXVII.). 

 Broom, Annals S, African Mus. 1913. 



In Scymnognathus tigriceps the basisphenoid is very large. It 

 has two greatly developed thick descending processes, which pass 

 down a considerable distance below the level of the condyle. In 

 front there is a deep but thin median keel, which passes forwards 

 and meets the median keel formed by the united pterygoids. 

 Above, the sphenoid passes between the pterygoids, and forms 

 a large median plate that extends forwards and upwards as far 

 as the plane of the front of the orbit. 



The pterygoid is a huge bone which more closely resembles the 

 pterygoid of the Pelycosaiu's than that of theother South- African 

 Therapsid suborders. The descending pterygoid process is very 

 large, but the most remarkable feature is the enormous develop- 

 ment of the ascending plates. These pass upwards and clasp the 

 front of the median sphenoid. In front of the sphenoid they 

 become ankylosed, and form a median plate which extends 

 forward to meet the vomer. Whether this large, thin, median 



