228 DR. R. BROOM ON 



plate is entirely made up of the fused pterygoids, or whether 

 there is a median basi-cranial element as well, cannot be made 

 out in the specimen. Certainly it is largely composed of the 

 pterygoid plates. In Scylacognathus the pterygoid plates are 

 separate from one another, and a median cartilaginous element 

 might have been between them. Further forward the median 

 plate in Scymnognathus is clasped by the ascending plates of the 

 palatines. In front of the median plate we meet with the vomer. 

 In Scymnognathus it clasps the front of the median plate, but in 

 Scylacognathus it is seen clasping a median element which is not 

 the fused pterygoids but may be regarded as ethmoid, a fact 

 which suggests that not improbably there is in Scymnognathus 

 an ethmoid element between the pterygoid plates, though no 

 sutures can be detected. There can, I think, be no question that 

 the vomerine bone is the true mammalian vomer. I can find no 

 evidence of paired prevomers. The relations of the palatine 

 bones, as viewed from underneath, can best be understood from 

 the figure of the condition in Scylacops (PI. XXXYI. fig. 3). 



The mandible is beautifully preserved in Scymnognathus, and 

 the condition is thus better known than in any of the Therapsidan 

 suborders. The outer aspect, of course, and something of the 

 internal relations of the bones, are known in all ; but there 

 are gaps in our knowledge even of the Anomodont mandible, 

 and only of the Gorgonopsian jaw is our knowledge practically 

 complete. Full detailed figures are thus given for later com- 

 parison with the other types (figs. 6 k 7). 



The dentary is large and powerful. The front of the jaw 

 is deep and formed by the dentary, except the base, which 

 is splenial. About two-thirds of the outer aspect of the jaw 

 are made up of the dentary, and there is a well-developed 

 coronoid process. Only a little of the dentary shows on the 

 inner aspects, as in front the inner side of the jaw is mainly 

 splenial, and further back most of the dentary is hidden by the 

 angular, gonial, and coronoid. The relations of these elements 

 to the dentary will best be understood by the section and figures. 

 The splenial extends backwards to opposite the point where the 

 angular begins to replace the dentary on the outer side. The 

 angular is the second largest bone in the jaw, and extends nearly 

 the whole length. In front it is fitted in between the dentary 

 and splenial. Posteriorly it forms the main part of the jaw. As 

 will be seen in the drawing, there is a curious doubling of the 

 back part, forming a deep groove for some structure. A very 

 similar condition is seen in Pelycosaurs, though, so far as known, 

 not in other Therapsida. There is a distinct coronoid bone, as 

 shown in the figures, lying on the inside of the back part of the 

 dentary. The surangular is of fair size and, with the angular, 

 forms most of the back third of the jaw. The articular is large 

 but short. It forms the articulation. It is clasped by the 

 angular and the gonial. It has a peculiar posterior process 

 which curves downwards and forwards. The gonial clasps the 



