South African Fossil Reptiles and Amphibia. 187 



posterior part of the ridge presumably basisphenoid is pierced 

 on either side by a large foramen, the upper border of which seems 

 to be formed by the periotic. This is presumably the fossa identified 

 by Watson in Diademodon as the pituitary fossa. A fracture 

 across the basisphenoid of the co-type just in front of the median 

 ventral ridge shows that the dorsal surface of the bone is broadly 

 rounded. 



The pterygoid is a large bone attached to its neighbour throughout 

 its length except where it forms part of the median keel, where 

 the two are separated by the anterior portion of the basisphenoid. 

 There is no interpterygoid vacuity. In front of the median keel 

 the bones form a broad plate which is hollowed out in the middle. 

 This hollowed portion occupies the position which is taken up by 

 the vomer in the Gorgonopsia and the Cynodontia ; but here are 

 no sutures to divide this portion from the rest of the pterygoid, 

 and the vomer, in consequence, seems to play no part in the 

 formation of this part of the palate. Moreover, the suture between 

 the two pterygoids can be traced almost throughout the length 

 of the plate-like portion. 



Laterally the pterygoid articulates with the transpalatine. It 

 forms the anterior boundary of the pterygoid vacuity 'and also 

 thickens to form the fairly small downward process or pterygoid 

 flange. The lower surfac" of this flange, however, is formed 

 entirely by the transpalatine. 



Anteriorly, the pterygoid narrows and passes forward as a narrow 

 bar between the palatines to meet the prevomer. The lateral 

 posterior ramus of the pterygoid passes outwards towards the 

 quadrate and lies in front of a thin inwardly-directed process of 

 the squamosal. A section across this ramus in the co-type shows 

 the ramus lying below a thin plate of bone with which it is slightly 

 interlocked. This thin plate is presumably part of the quadrate. 

 The pterygoid is separated fairly widely from the paroccipital. 

 Attached to the outer side of this ramus is the epipterygoid or 

 columella cranii. This is a broad bone lying pressed against the 

 pterygoid below and the parietal above. Its upper articulation 

 is long ; its anterior upper end lies considerably in advance of 

 the lower end ; and its anterior border is concave. Posteriorly 

 its lower half extends far back, while the upper half articulates 

 with the periotic. The bone occupies the same position and is 

 of similar shape to the pterygoidal portion of the side-wall of 



