Structure of the Therocephalian Skull. 75 



opistliotics, resembling fairly closely that of Sphenodon ; in 

 tiie Cyiioilont it opens entirely downwards on the extreme 

 lower snrfnce of the cranium. 



Other tratures of the pahite which di'serve mention are 

 the small interpteryj^oid vacuity and the absence of any 

 suboibital vacuiiies. 



It is certain that, although the matrix cannot be removed 

 so as to show it, the parasphenoid lying above the level of 

 the palate really divides the vacuity. This condition is 

 exactly similar to that in Anomodonts, where the pterygoids 

 meet below the parasi)henoid, and then separate to form a 

 large interpterygoid vacuity which is divided by tlie jiara- 

 sphenoid lying above the levcd of the palate. The higher 

 Cvnodonts show an advance on the mammalian direction 

 in the compute obliteration of the interpterygoid vacuity 

 and the exposure of tiie paras[)henoid (mammalian vomer) 

 for its whole length. The remaikable Cynodont type ]\Jicro- 

 gonipliodon oligocynus, which may, I think, be included in 

 the same family with Buuria, has a large interpterygoid 

 vacuity. 



The condition of the parietal region of the Gorgonopsid 

 skull is of great interest. The extension of the postorLital 

 backwards to meet the squamosal, and the consequent exclu- 

 sion of the postfrontal and parietal from the border of the 

 temporal fossa, occurs also in Deinocephalia, Diruetrodon, 

 L)iomasauria, and Anomodonts; it iias thus every appearance 

 of being a primitive Tliera|)sid character. When 1 described 

 the skull of Diudemudon I thought it most probable that it 

 was a secondary feature; but examination of much more 

 material, including particularly some of that in South Africa, 

 has convinced me that Dr. Broom was quite justified in 

 holding it to be primitive. It does not therefore follow that 

 lie is right in holding that the Therapsid temporal fossa is 

 homologous with the lower one of Sjdtenudon. The fact that 

 in all iJiapsid reptilfs except Sphenodon the quadrato-jugal 

 foinis part of the border of the lower temporal fossa and 

 that in the jJeinocephalia the squamosal meets the post- 

 orbital below the lossa, and tiiat these two bones form a good 

 deal of the zygomatic arch in all Therapsids, seems to me to 

 show that the Therapsid temporal fossa is not homologous 

 with either of those of Sphenodon^ but is really developed in 

 the ujiper temporal arcade of that reptile, being primitively 

 bonndeti by the squamoj^al and postorbital alone. By increase 



