CRYPTODONTIA. 243 



suppose that they were originally buried in the sandy matrix 

 which afterwards hardened around them ; and since lizards, 

 owing to the unlimited reproduction of their teeth, do not 

 become edentulous by age, we must conclude that the state in 

 which the Rhynchosaurus was buried, with its lower jaw in un- 

 disturbed articulation with the head, accorded with its natural 

 condition, while living, so far as the less perishable hard parts 

 of its masticatory organs were concerned. Nevertheless, since 

 a view of the inner side of the alveolar border of the jaws has 

 not been obtained, we cannot be quite assured of the actual 

 edentulous character of this very singular Saurian. The indica- 

 tions of a dental system are much more obscure in the Rhyn- 

 chosaurus than in any existing Lacertian ; the dentations of the 

 upper jaw are absolutely feebler than in the chameleon, and no 

 trace of them can be detected in the lower jaw, where they 

 are strongest in the chameleon. The absence of the coronoid 

 process in the Rhynchosaurus, which is conspicuously developed 

 in all existing lizards, corresponds with the unarmed condition 

 of the jaw, and the resemblance of the Rhynchosaurus in this 

 respect to the Chelys fcrox, would seem to indicate that the 

 correspondence extended to the toothless condition of the jaws. 

 The resemblance of the mouth to the compressed beak of 

 certain sea-birds, the bending down of the curved and elon- 

 gated premaxillaries, so as to be opposed to the deep symphysial 

 extremity of the lower jaw, are further indications that the 

 ancient Ehynchosaur may have had its jaws encased by a bony 

 sheath, as in birds and turtles, the dentinal ends of the pre- 

 maxillaries projecting from, or forming, the deflected end of 

 the upper mandible. 



There are few genera of extinct reptiles of which it is more 

 desirable to obtain the means of determining the precise 

 modifications of the locomotive extremities than the Rhyncho- 

 saurus. The fortunate preservation of the skull has brought 

 to light modifications of the lacertine structure leading towards 



