158 



REPTILIA. 



posterior nares (pt. na.) are scarcely if at all covered by the 

 secondary development of palatine plates, and the very large 

 pterygoids (pt.) meet in the middle line in advance of the 

 basisphenoid, though leaving a small median vacuity (ptfo.). 

 The mandible exhibits no coronoid process, but is pierced by 

 a large lateral vacuity. As to other features in the cranial 

 osteology there is still difference of opinion, owing to the 

 difficulty of distinguishing sutures and cracks. The accom- 

 panying diagrams, however, give one plausible interpretation 

 of the arrangement of the bones in Gordonia (fig. 99). No 

 complete skeleton of a Dicynodont has hitherto been discovered, 

 but many portions of the trunk have been placed here with 

 much probability of correctness, and they agree closely with 

 the corresponding bones of the Theriodonts. Characteristic 

 pectoral and pelvic arches are shown in figs. 101 A, B. 



FIG. 101. 



Eight Pectoral Arch, outer aspect (A), and right Pelvic Arch, outer and inferior 

 - aspects (B), of a Dicynodont Eeptile, much reduced. Karoo Formation 

 (Permian or Triassic) ; Cape Colony. a., acromial process ; ac., glenoid 

 cavity for humerus, and acetabulum for femur; co., coracoid; ep.co., epi- 

 coracoid; il., ilium; is., ischium; pb., pubis; sc., scapula. (Eestored from 

 specimens in British Museum.) 



The skull of the typical Dicynodon, from the Karoo Forma- 

 tion of Cape Colony, sometimes attains a length of 0'5 m. (D. 



