94 MR. D. M. S. WATSON ON THE 



When the structure of the skull of a Gorgonopsid was dis- 

 covered, Broom and I independently pointed out the many 

 resemblances which it presented to Dicynodonts in the inter- 

 temporal, basicranial, and other regions. 



These resemblances are real, but, with the exception (?) of the 

 occurrence of a preparietal, lie entirely in the common possession 

 of primitive Anomodont characters, such as the broad parietal 

 surface and the main features of the basis cranii. When con- 

 sidered in more detail, the structure of such a Dicynodont as 

 Endothiodon seems to show no such resemblance to that of a 

 Gorgonopsid as to imply any closer connection between the 

 two groups than either of them bears to the Deinocephalia 

 or Dromosauria. The secondary palate of Endothiodon is dif- 

 ferent in type from that of Diademodon and all the forms of 

 Gorgonopsids leading up to it. In them, as in mammals, the 

 original vaulting of the palate is brought about by a down- 

 growth of the tooth-bearing edge of the maxilla below that of 

 the premaxilla ; the internarial bar remains attached to the 

 ends of the palatal processes of the premaxilla?, and when the 

 secondary plates of the maxilla? grow out they lie ventral to 

 the palatal parts of the premaxilla?. In fact, the original surface 

 of the palate lies on the roof of the naso-pharyngneal duct, the 

 sides of the palate growing clown below it. 



In Endothiodon (text-fig. 29), on the other hand, the palatal 

 surface of the premaxilla? lie in the same plane as that of the 

 maxilla? and transverse bones, the posterior nares open into a 

 c | ee p groove, excavated in the original palate, which is roofed 

 by a great forward growth of the prevomers over the region 

 formerly occupied by the large posterior nares. 



Thus it appears that the palate of Dicynodonts does not 

 present a real resemblance to that of Gorgonopsids, but repre- 

 sents a different mode of development of a secondary palate, 

 identical with that of a Ghelonian. One of the most striking- 

 features of the Dicynodont palate is the loss of the pterygoid 

 flanges, which are only represented by slight eminences on the 

 edge of the narrow posterior part of the palate over the pterygo- 

 transverse suture. This loss seems to be due to the very great 

 expansion of the temporal muscles squeezing them out of exist- 

 ence, their presence not being necessary to insure accurate closure 

 of the mouth in an animal without a closely -fitting dentition — in 

 some cases their function being taken over by the long canines, 

 which often present wear-faults on their inner sides in large 

 Dicynodonts. 



When allowance is made for the changes resulting from the 

 development of the horny covering of the edges of the jaws and 

 the extension of the crushing palate, it is readily seen that the 

 main plan of the anterior part of the Endothiodon palate is 

 reducible to that found in Therocephalia, except for the absence 

 of suborbital fenestra?. 



Posteriorly, however, there is in Dicynodonts no trace of the 



