Royal Society. 65 



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 vertebrae 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 stated 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. 



Pectoral arch. — A perfect scapula discovered in the strata of Til- 

 gate Forest, and which corresponds with the coracoid bone, provi- 

 sionally assigned to the Iguanodon in the memoir of 1841 (Phil. 

 Trans. PI. IX. fig. 11), Dr. Mantell has been enabled to refer to that 

 re^itile, by the fortunate interpretation of portions of two scapulae 

 which are preserved in the Maidstone specimen, but had not pre- 

 viously been recognized as such. As the clavicles were long since 

 determined, the essential elements of the pectoral arch are now as- 

 certained, and the author gives a restored outline of this important 

 part of the skeleton, based upon these data. 



Humerus. — A humerus three feet long, discovered by Mr. Fowles- 

 tone in the Isle of Wight, has been ascertained by the author to belong 

 to the Iguanodon, from the presence of a small but corresponding 

 bone in the Maidstone fossil. This bone, from its disproportionate 

 size in comparison with the femur with which it is collocated — being 

 one-third shorter — was formerly assigned by Dr. Mantell to the fore- 

 arm ; but the large humerus from the Isle of Wight, which, except 

 in magnitude, is identical with that from Maidstone, leaves no doubt 

 upon the subject. It is now therefore, for the first time, ascertained, 

 that in the Iguanodon, as in many fossil and recent reptiles, the an- 

 terior extremities were much shorter and less bulky than the poste- 

 rior. The radius and ulna are still undetermined, but the author 

 states that there are some imperfect bones in his former collection, 

 now in the British Museum, which he thinks will be found to belong 

 to the fore-arm. 



Hinder extremities. — The colossal magnitude of the Iguanodon is 

 strikingly shown by some femora- and leg-bones recently discovered. 

 One femur is 27 inches in circumference, and must have been 4 feet 

 ¥hiU Mag. S. 3. Vol. 35. No, 233. July 1849. F 



