the [lomologies of the Lizard^s Skull. 85 



identification with the mammalian bone. I have recently 

 endeavoured to show by direct traein;^ from a mammal 

 down the Tlierapsid line to the ])rimitive Varanosnurus that 

 it is really the true mammalian scjuamosal. 



In all the Therapsid reptiles the relations of the squamosal 

 are very constant. 



In all it forms a large part of the border of the temporal 

 fossa, sending a long ])rocess forward on the anterior face 

 of the i)arietal which in early ty|)e.s actually meets a similar 

 backward jjrolongation of the postorljital. Below the fossa 

 it sends forward a similar process above and within the jugal 

 towards the j)ostorbital, which in many early types sends 

 back a similar process lying above and without the jugal to 

 meet it. These two processes meet and form the body of 

 the bone, which has a powerful articulation with the outer 

 end, and in some cases (e. g., Enduthiodon and Diademodun) 

 with a small area of the anterior face of the paroccipital ; 

 to the outside of this articulation the bone passes down and. 

 out behind the quadrate. In Varanosaarus the part of the 

 squamosal which lies below the articulation with the par- 

 occipital is in contact with the posterior end of the quadrate 

 ramus of the pterygoid, precisely as in Pteroplax and 

 Seijinouria. In most types, owing to the reduction of the 

 pterygoid, this no longer happens. AVheu an unreduced 

 quadrato-jugal is present (^Deinocephalia, Dimetrodon), it is 

 articulated with the outer edge of the quadrate and the 

 lower edge of the squamosal, and passes forward within and 

 below the posterior end of the jngal. 



So far as I have been able to observe^ the directions of 

 overlap of bones given above are constant for all Therapsids. 



In tlie great majority of Therapsids a tabular is present. 

 In all cases it lies entirely behind the parietal and squamosal 

 ou the posterior surface of the skull, and commonly reaches 

 down outside the post-temporal fossa to touch the posterior 

 upper corner of the end of the paroccipital. 



In the skull of Sphenodon (fig. 1 A) there is a single bone 

 in the temporal region ; the work of Swinnerton and Howes 

 has shown conclusively that this is really single in origin. 



In the adult animal it has the following relation^hips : — 



It forms a large part of the border of the temporal fossje, 

 sending a long process forward on the anterior face of the 

 parietal and a similar process forward within the corre- 

 sponding backward process of the postorbital. A third 

 ramus passes downwards and forwards along the upper and 

 inner side of the jugal ; this last ramus covers some of the 

 front edge of the quadrato-jugal. 



