74 Mr. D. M. S. Watson on the 



sliows that the Therocephalia agree very closely with such a 

 Cj'iiodont as D'lademodon in the structure and relations of 

 the basisplienoid and paiasphenoid to the pterygoids. 



There thus seems to be no room left for doubt that 

 Dr. J5room is quite correct in his contention that the 

 niamniahan vomer is homologous with the reptilian para- 

 sphenoid and that the reptilian vomers, the pre vomers, are 

 lost in tiie majority of recent mammals. 



The skull described in this paper seems to show a rather 

 more primitive condition of the articulation of tiie pterygoid 

 with the basis cranii than occurs in Diademodon. There 

 is a distinct basipterygoid process, and the connection between 

 tlie pteiygoids and the parasphenoidal rostrum seems not so 

 close as in the more recent type. 



One very remarkable feature of tlie Gorgonopsidai is the 

 extreme shortness of the posforbital part of the skull and its 

 remarkable length in front of the orbit. The short cranial 

 region is paralleled by all the Deinocephaliaus, Droma- 

 saurians, and Dimetrodon, and seems to be undoubtedly a 

 primitive Therapsid character. 



The great elongation of the face occurs in Therocephalia, 

 Titanosuchus amongst the Deinoct^phalia, and Dimetrodon; it 

 does not occur in Edaphosaurus, Moscops and allied Deino- 

 cephalia, Dromasauria, and Anomodonts ; it is noticeable 

 that all these types with an abbreviate face are or may be 

 herbivorous, there being no large canine in any of them 

 except Bici/nodon, Avhere its occurrence seems to be a secon- 

 dary sexual character. There is thus coiisiderable reason for 

 suppo.>«ing that the elongated face, like the deepening of the 

 maxilla, is an adaptation to tiie development of a powerful 

 carnivorous dentition. It is probable that this lengthening 

 is the cause of the enormously long prevomers and of the 

 long region where the pterygoids are in contact with the 

 paraspheiioid in Therocephalia. The curious position of the 

 basi pterygoid process of the basisphenoid, which is dorso- 

 ventrally flattened and laterally directed, seems to depend 

 entirely on the reduction of all the parts of the skull which 

 lie below the opistliotics. This reduction is progressive ; it 

 is scarcely shown in the Pelycosauria and perliaps Deino- 

 cephalia, is very marked in Therocephalia, and still more so 

 in Cynodontia. One interesting case of it is well brought 

 out by comparison of the position of the foramen jugulare of 

 the Tlierocephalian described aboye with that of Diademodon. 

 In the earlier type it is directed very nearly backwards and 

 lies considerably above the level of the bottom of the 



