ROOM III. CONVEXO-CONCAVE CERVICAL VERTEBRAE. 261 



the South-East of England" : "The vertebrae of the fourth 

 system are very rare ; they are of the true lacertian type, 

 having the articular facets of the body convex posteriorly and 

 concave anteriorly, and are wider than high, as in the Iguanas 

 and Monitors, and not in the reverse proportion, as in the 

 existing Crocodiles. In two large but mutilated cervicals, the 

 admeasurements are as follow : 



Heisrht of the concave extremity .... 3 J inches. 



Width of the same 4 



Length of the body 6 



" It is not obvious whether the annular part be united by 

 suture or otherwise ; the articular apophyses are horizontal 

 and very strong, the spinous process is destroyed." 1 In the 

 same work, (p. 307) when referring provisionally the "somewhat 

 angular dorsal and caudal vertebrae" to the Iguanodon, I men- 

 tion " that the above cervical vertebrae correspond so entirely 

 with those of the Iguana and Monitor, that it would > seem 

 a more probable conclusion that they belonged to this herbi- 

 vorous reptile : yet the extreme rarity of this type renders it 

 questionable, since there appears no reason why the vertebrse 

 should not have been found in as considerable numbers as the 

 teeth." On this statement Professor Owen remarks, " It is 

 the fortunate preservation of the two articular or oblique 

 processes at one of the extremities of the annular part of this 

 fine vertebra, now in the Mantellian Collection, Brit. Mus. 

 No. ZTTS, that has enabled me to correct the error into which 

 the Founder of that noble collection has in this instance 

 fallen. The flat oblong articular surface of each of the strong 

 and well-marked oblique processes looks downwards and out- 

 wards, thus determining them to be the posterior pair ; and 

 they overhang the concave extremity of the body of the ver- 

 tebra, showing that to be the posterior part. The opposite, or 

 anterior end of the body of the same fossil is convex. The 

 few other large convexo-concave vertebrae from the Wealden 

 of Tilgate correspond with the one here described in these 

 important characters of the genus Streptospondylus, and 

 equally differ from the vertebrse of the Iguance, Monitors, 

 and all existing Sauria. Of the fossil cervical vertebra six 



1 " Geology of the S.E. of England," 1833, p. 300. 



