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



111 side-view the skull of Varanosaurus sliows a long shallow 

 inaxillii, completely separated from the nasal by the long lachrymal 

 extending from the orbit to the septomaxilla. There is no ver}' 

 marked specializn.tion of the dentition, all the teeth from the 

 premaxilla backward being similar in form and not very dis- 

 similar in size. The quadrato-jugal is exposed on the side-wall of 

 the skull and the jugal stops considerably before the quadrate. 



Diadeviodon has a short deep nui.xilla reaching the nasal in a 

 long suture. The lachrymal is a small short bone. The dentition 

 is fully divided into incisor, canine, " premolai'," and " molar 

 teeth." 



The quadrato-jugal no longer ajjpears on the surface of the 

 skull and the jugal extends back to its extreme hinder end. 



The suspensorium of Varanosaurus consists of a large quadrate 

 with a definite pterygoid wing, whose posterior surface is covered 

 by the pterygoid. 'J'he outer edge of the quadra.te is attached to 

 the quadrato-jugal, there being no quadrate foramen. The upper 

 part of the posterior surface of the quadrate is covered by 

 the squamosal, that bone passing so far inwards as to touch the 

 pterygoid. 



In Diademndon the quadrate is a very small bone, either with 

 or without a pterygoid wing, but in no case articulating with the 

 pterygoid. The outer edge of the quadrate is fused with the 

 quadrato-jugal, from which it is separated only by a small foramen, 

 the articular surface being formed about equally by either bone. 

 The whole posterior surface of the joint bone is covered by the 

 very la,rge squamosal, which extends down to the condylar edge. 



The primitive Pelycosaur palate has the following characters : — 

 The pterygoid is a triradiate bone, articulating by a movable 

 facet with the basipterygoid process, from which point the 

 qviadrate ramus rises and runs backward as a vertically placed 

 sheet of bone, passing behind the quadrate. The lateral wing of 

 the pterygoid passes directly outward from the region of the 

 basipterygoid and terminates in the usual flange. 



The anterior part of the pterygoid forms a large part of the 

 essentially fiat palatal surface and articulates with the prevomer. 

 It meets its fellow in median suture in Varanosaurus. The 

 dorsal surface of the pterygoid is raised into a ridge near the 

 middle line of the skull. In later forms {Dimetrodon, e. g.), the 

 ridge is much exaggerated and its median surface passes 

 smoothly into the ventral surface. The palatines are small flat 

 bones. The prevomers are distinct. The anterior end of the 

 palate is not known in any primitive Pelycosaur, but from 

 the conditions in later forms there is no doubt that the posterior 

 nares were small and lay in the general plane of the rest of the 

 ])alate, which was essentially fiat. In such later Pelycosaurs as 

 Dimetrodon, owing to the step in the lower edge of the maxilla, 

 the palate is consiilerably vaulted, and the posterior nares lie 

 above the level of the cheek-teeth. 



In BiadeinodoiithG pterygoid ai^ticulates by a rigid suture with 



