805 



detached, and for the most part mutilated bones of the spinal column, 

 Dr. Mantell expresses his deep obligation to Dr. G. A. Melville, 

 whose elaborate and accurate anatomical description of the vertebras 

 is appended to the memoir. The most interesting fossil remains are 

 described in detail in the following order. 



Lower Jaw. — Since the author's communication on the lower jaw 

 of the Iguanodon, published in the Philosophical Transactions, part 

 ii. ] 848, he has discovered the right angular bone, which was pre- 

 viously unknown : from the circumstances under which this relic 

 was found, he considers it probable that it belonged to the same 

 individual as the teeth figured in Plate XVIII. of the Philosophical 

 Transactions for 184?8. 



Vertebral colim^i.-— The vertebrae hitherto assigned to the Igua- 

 nodon consist of the middle and posterior dorsal and anterior cau- 

 dal, as identified by means of the Maidstone specimen in the British 

 Museum : the cervical, anterior dorsal, lumbar, and posterior and 

 terminal caudals, were previously either undetermined or referred to 

 other genera of saurians. The investigations of Dr. Melville have 

 established the important and highly interesting fact, that the cervi- 

 cal and anterior dorsal vertebrae of the Iguanodon were convexo- 

 concave' — that is, convex in front and concave behind — as in the 

 fossil reptile of Honfleur termed Slreptospondi/lus, and in the exist- 

 ing pachyderms ; the convexity gradually diminishing, and the an- 

 terior face of the body of the vertebra becoming flat, in the middle 

 and posterior part of the dorsal region. The supposed Streptospon- 

 dylian vertebrae of the Wealden (named S. major by Professor Owen 

 in British Association Reports on fossil reptiles) are, in the opinion 

 of the author and Dr. Melville, the true cervical vertebrae of the 

 Iguanodon. The convexo-concave type of vertebrae was not con- 

 fined to a single genus — the Streptospondylus of the Oolite — but 

 prevailed in two, and probably in several, genera of extinct sau- 

 rians of the secondary geological epochs ; in like manner as the re- 

 verse form, the concavo-convex, predominates in the existing cro- 

 codilians and lizards. 



Other large vertebrae found with ribs and bones of the extremities 

 of the Iguanodon, and referred by Professor Owen to one or more 

 species of Cetiosaurus, are regarded, in consequence of the peculiar 

 structure of the neural arch, as belonging to the posterior dorsal and 

 lumbar vertebras of the former colossal reptile ; and certain some- 

 what angular vertebrae, also previously assigned to a species of Ce- 

 tiosaurus, are presumed to be the middle and distal caudals of the 

 Iguanodon. 



The Sacrum, of which portions of several examples belonging to 

 individuals of much disparity in size have been obtained, is shown to 

 consist of six anchylosed vertebrae ; not of Jive, as described by Pro- 

 fessor Owen ; and the typical specimen in the possession of Mr. Saull, 

 which the author figures and describes, is adduced in proof of the 

 correctness of this opinion. The anterior vertebra, and the two 

 posterior ones, are much larger and stronger than the three inter- 

 mediate elements which occupy the centre of the arch of the sacrum. 



