MAMMAL-LIKE REPTILES. 229 



inner side of the articular in front, and extends forwards between 

 the coronoid and the angular to a little beyond the posterior end 

 of the splenial. 



POSTCUANIAL SKELETON. 



The upper cervical vertebrse are very similar to those in other 

 Therapsidans. The proatlas is large, and the upper portion 

 of the atlas is very similar to that in Anomodonts and Dino- 

 cephalians ; and the condition further resembles that of these 

 suborders in the two halves being free and not forming a single 

 arch as in Cynodonts. 



The shoulder-girdle has a large scapiila without any distinct 

 a.cromion process. The coracoid and precoracoid resemble those 

 of the Therocephalians. There is a distinct cleithrum (at least 

 in Scylacops), a large clavicle and interclavicle, and an ossified 

 sternum. 



The carpus has a large radiale and ulnare and a small inter- 

 medium. There are two centralia, of which the outer is the 

 smaller. There are four distal carpalia, but the fourth is very 

 broad and, I believe, formed of the ankylosed fourth and fifth. 



The digital formula is 2, 3, 4, 5, 3 ; the third toe having a 

 small phalanx and the fourth two small phalanges as in the 

 Therocephalia. 



Yery little is known of the posterior half of the body. 



Affinities of the Gorgonopsia. 



Till we know more of the structure of the Therocephalia it is 

 impossible to say how far the Gorgonopsia differ. The differences 

 in the skull may be tabulated as follows : — 



Gorgonopsia. Therocephalia. 



1. Parietal region broad. Parietal region narrow. 



2. A preparietal bone. No preparietal bone. 



3. A large postfrontal. Postfrontal small or absent. 



4. Postorbital large, forming the Postorbital small, not extend- 



upper temporal margin and ing far back and not meet- 

 meeting squamosal above. ing squamosal above. 



5. A single median true vomer. A pair of prevomers. 



6. Transpalatine closely united Transpalatine separated from 



to pterygoid. pteiygoid by large foramen, 



7. Mandibles united by powerful Jaws loosely articulated. 



symphysis. 



8. Angular with deep groove. Angular perforated. 



Most of the characters in which the Gorgonopsia differ from 

 the Therocephalia are characters in which they agree with the 

 Anomodontia. The Therocephalia ai^e unquestionably the more 

 primitive group, but there are some early characters in the 

 Gorgonopsia and also in the Anomodontia. Of course we only 

 know well one or two of the later Gorgonopsians, and we have 

 good reason to believe that the group is very early — earlier in 



