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



most probable, from the analogies of similarly shaped jaws of existing Reptilia, 

 that the fore-part of both the upper and under jaws were sheathed with horn. 



Amongst existing Reptilia, the Siren alone combines this structure with true 

 teeth : but these are minute and numerous, and disposed upon the palate in the 

 upper jaw, and upon the opercular piece of the lower jaw: in other respects the 

 cranial structure of the Siren is as remote from that of the Dicynodon as can well 

 be in any Reptile, if we may be permitted so to call the Siren. It is the chief and 

 best-known characteristic of the Turtles and Tortoises to have the jaws sheathed with 

 horn, as those of the Dicynodon appear to have been ; but no known member of 

 the Chelonian order has any true teeth*. Until the discovery of the Rhynchosau- 

 rus, this edentulous and horn-sheathed condition of the jaws was supposed to be 

 peculiar to the Chelonian order among Reptiles ; and it is not one of the least 

 interesting features of the Dicynodon of the African sandstones, that it should repeat 

 a Chelonian character, hitherto peculiar, amongst Lacertians, to the remarkable ex- 

 tinct edentulous genus of the new red sandstone of Shropshire : but our interest rises 

 almost to astonishment, when, in a Saurian skall, we find superadded to the horn- 

 clad mandibles of the Tortoise a pair of tusks, borrowed as it were from the Mam- 

 malian class, or rather foreshowing a structure, which in the present existing 

 creation is peculiar to certain members of the highest organized warm-blooded 

 animals. 



The Reptilian nature of the Dicynodon is not more strongly evidenced by 

 the characters of the cranial and facial bones, than by the compound structure 

 of the lower jaw : that attached to the skull of the Dicynodon lacerticeps has had 

 most of its exterior surface splintered and broken away : a portion of a detached 

 lower jaw of apparently the same species of Dicynodon shows the entire anterior 

 end, and gives the two sections 5 and 6 in Plate IV. But, before speaking of the 

 traces of the sutures thus exposed, the general form of the lower jaw may be more 

 particularly noticed (PL III. fig. 1 .) . It gradually increases in depth from the pos- 

 terior articulation forwards to the symphysis, which then expands more suddenly in 

 the vertical direction and curves slightly upwards ; the rami converge at a very acute 

 angle in approaching that part, and suddenly bend inwards at their lower border 

 to join and form the symphysis (PI. IV. fig. 4, 24), at a distance of three inches and 

 a half from the posterior articulation ; the whole length of the lower jaw being 

 four inches and a half, perhaps five inches, including the posterior angle, which in 

 the present example is broken away on both sides. The depth of the ramus imme- 

 diately in front of the articulation is nearly one inch ; at the middle of the ramus it 



* In the Trionyx rudiments of teeth are present in the embryo, and this is probably the case in other 

 Chelonia; but they are numerous, equal, and very minute. See my ' Odontography,' p. 179. 



