ANOMODONTIA. 157 



Sub-Order 3. Dicynodontia. 



The most specialized group of Anomodonts exhibits either 

 toothless jaws or the dentition reduced to a single pair of tusk- 

 like teeth in the maxillae growing from persistent pulps. They 

 are named DICYNODONTIA in allusion to the latter feature 

 (fig. 99). The external bones are never sculptured. There is 

 a large supratemporal vacuity (tern.), and the squamosal bone 

 (sq.) is enormously developed, not only forming the greater part 

 of the single broad temporal arcade but also produced into a 



b.fJCG. 



Fro. 100. 



Ptychognathus declivis ; occipital view of skull, nearly half nat. size. Karoo 

 Formation (Permian or Triassic) ; Cape Colony, au., supposed auditory 

 opening; b.occ., basioccipital ; exocc., exoccipital ; f.m. , foramen magnum; 

 pa., parietal; s.occ., supraoccipital ; sq., squamosal. (Restored from 

 specimen in British Museum, no. 36221.) 



deep stout pedicle (sq. p.) over the comparatively small quadrate 

 (qu.), which is exposed only quite at the end for the articulation 

 of the mandible. The basioccipital (fig. 100, b. occ.) enters the 

 occipital condyle and imparts to it the trefoil aspect well-known 

 in Chelonia. The occiput (fig. 100) is an upright flattened 

 plate, usually with only one pair of small vacuities (? auditory 

 openings, au.) at the outer margin of the exoccipitals (exocc.) ; 

 the antorbital region is shortened and more or less bent down- 

 wards ; the premaxillae (fig. 99, pmx.) are fused together. The 



