





Zoology. 439 



4. Additional Observations on the Osteology of the Iguanodon and 

 Hylaosaurus ; by Gideon Algernon Mantell, Esq,, L.L.D., F.R.S., 



Vice President of the Geological Society of London, &c, (Proceedings 

 of the Royal Society, March, 1849. The Marquis of Northampton in 

 the chair.) — This memoir, which is supplementary to the author's for- 

 mer communications to the Royal Society on the same subject, com- 

 prises an account of some important additions which he has lately made 

 to his previous knowledge of the osteological structure of the colossal 

 reptiles of the Wealden strata of the southeast of England. 



The recent acquisition of some gigantic and well preserved vertebrae 

 and bones of the extremities from the Isle of Wight, and of other in- 

 structive specimens from Sussex and Surrey, induced the author to re- 

 sume his examination of the detached parts of the skeleton of the 

 Wealden reptiles in the British Museum and in several private collec- 

 tions ; and he states as the most important result of his investigations, 

 the determination of the structure of the vertebral column, pectoral 

 arch, and anterior extremity of the Iguanodon. In the laborious and 

 difficult task of examining and comparing the numerous detached and 

 in most instances mutilated bones of the spinal column, the author ex- 

 presses his deep obligations to Dr. G. A. Melville,* whose careful and 

 elaborate description of the vertebrae forms an appendix to the memoir. 

 The most interesting fossil remains figured and described, are the 

 following : — 



Lower Jaw. — Since the author's memoir on the maxillary and dental 

 organs of the Iguanodon,f he has discovered the right lingular bone ; 

 and from the circumstances under which this relic was found, he con- 

 siders it probable that it belonged to the same individual as the teeth 

 figured in the Philos. Transactions, for IN 18. 



Vertebral column. — The vertebrae hitherto assigned to the Iguanodon, 

 consist of the middle and posterior dorsal and anterior caudal, as es- 

 tablished by the Maidstone specimen in the British Museum; the cer- 

 vical, anterior dorsal, lumbar, and posterior and terminal caudal, were 

 previously either undetermined, or referred to other and distinct genera 

 of saurians. The investigations of Dr. Melville and the author, have 

 established the important and highly interesting fact, that the cervical 

 and anterior dorsal vertebrae of the Iguanodon were convexo-concave 

 that is, convex in front and concave behind, as in the fossil genus termed 

 Streptospondylus, and in the existing pachyderms. The convexity 

 gradually diminishes and the anterior face of the vertebrae becomes flat 

 in the middle and posterior part of the dorsal region. The supposed 

 Streptospondylian vertebrae of the Wealden, referred by Professor Owen 

 to a new species (Strep, major), are true cervical vertebra of the Igu- 

 anodon. The convexo-concave type of vertebrae was not, in the opin- 

 ion of the author, confined to a single genus — the Streptospondylus of 

 the oolite — but was present in two, and probably in several genera of 

 extinct saurians of the secondary geological epochs, in like manner 

 as the reverse forms — the concavo-convex — prevail in the recent 



* One of the authors of the Work on the Dodo, reviewed in this volume, p. 5 V 2 

 f See preceding page. 



