64 Prof. Owen on the Reptilian Fossils of South Africa. 



or temporal bones (27, 27). In the strength of these bones and their continuation 

 from the lower part of the post-orbital wall, the Dicynodon much more resembles 

 the Crocodilians, especially the extinct forms, than it does the Lacertians : the zy- 

 gomatics are nevertheless continued, as in most Lacertians, to the upper, and not 

 to the lower end of the tympanic pedicles, as they are in the Crocodiles. 



In some existing Lacertians, as the Acrodont species figured*, the temporal va- 

 cuities are over-arched by two bony bridges extended in the axis of the skull, one from 

 the upper angle of the orbit, formed by the post-frontal and mastoid, to the upper 

 end of the os tympanicum ; the other from the lower angle of the orbit, formed by 

 the malar and zygomatic, to the lower end of the os tympanicum. This is essentially 

 a repetition of a Crocodilian structure ; the extinct Teleosaurus most resembling 

 the Lizard cited in the length and slenderness of the two bridges. The Rhyncho- 

 saurus of our own new red sandstones seems to have presented the same structure; 

 but part of the lower or zygomatic bridge is broken off in the only specimen of the 

 skull of that genus I have hitherto seen. The exact shape and vertical extent of 

 the strong single bridge formed by the zygomatic and mastoid, in the Dicynodon, 

 cannot be determined in the present fossil, in which the upper border is broken 

 away. In the formation and position of the single zygomatic arch, the Dicynodon 

 most resembles the genus Testudo ; only the arch abuts against a smaller propor- 

 tion of the upper and anterior border of the os tympanicum in the bidental fossil. 



The part of the single narrow parietal bone which separates the temporal fossae 

 from each other is impressed on each side by an oblique smooth tract, indicating 

 the origin of the strong temporal muscle ; the upper boundary-ridges of the tracts 

 almost meet along the posterior half of the parietal, but diverge as they advance 

 forwards and curve outwards to be continued upon the post-frontals. The inter- 

 mediate flat, triangular space of the parietal included by these diverging lines is 

 perforated by a small elliptical foramen : this character of the parietal bone is pe- 

 culiar, amongst existing Reptiles, to the Lacertia, though far from being constant in 

 that order : it appears to have been present in the skull of the extinct Pistosaurus. 

 The relative position of the foramen is the same as in the Rhynchocephalus figured 

 and in the great Monitor Javanicusf, behind the transverse sagittal suture ; not, as in 

 the Iguana\, upon that suture. The posterior part of the parietal bone of the Dicy- 

 nodon expands and bifurcates ; this is also a peculiarly Lacertian character. The 

 extremities of the parietal forks (8', 8') unite with the strong mastoids (7, 7), which 

 receive the extremities of the zygomatics (27), and form, with them, the medium 

 of attachment of the tympanic pedicles to the cranium. These are strong bones 



* PI. VI. figs. 5, 6, 7. 



f Cuvier, Ossemens Fossiles, 4to, 1824, vol. v. part 2. pi. xvi. fig. 7. 



I lb. fig. 23. 



