88 Dv Mantell on the Structure of the lyuanodon, 



Mantell proceeded to illustrate the structure of the Iguanodon as 

 exemplified by the isolated parts of the skeleton hitherto discovered, 

 and of which numerous examples were exhibited on the tables of 

 the Institution. 



The perfect germ, and the unused tooth, of the Iguanodon, are 

 characterised by the prismatic form of the crown, which is traversed 

 on the thick enamelled face by three or four longitudinal ridges, and 

 has the lateral margins denticulated, and the summit finely crenated ; 

 in this state the teeth resemble those of the living Iguana of the 

 West Indies — a resemblance which suggested the generic name of 

 Iguanodon. But the fossil teeth are of enormous size in comparison 

 with their recent prototypes ; for the teeth of the Iguana are as 

 small as those of the mouse, while those of the Iguanodon are often 

 one inch wide, and three inches in length. Specimens exhibiting 

 the above characters are, however, rare ; the summit of the crown 

 is usually more or less worn away by use, and the fang removed by 

 absorption from the pressure induced by the upward growth of the 

 successional teeth. In the first example discovered by Dr Mantell 

 (in 1820), the crown was ground down so as to present on its inner 

 face a smooth oblique surface with a cutting edge on the summit, 

 and the marginal crenations were worn away. In this state the 

 fossil so strikingly resembled an upper tooth of a rhinoceros, that 

 Baron Cuvier pronounced it to belong to a species of that genus. 

 Numerous teeth in different stages of growth and detrition were at 

 length obtained, and the reptilian character of the animal to which 

 they belonged was satisfactorily determined. Three years since, 

 the first specimen of the lower jaw was discovered by Captain Lam- 

 bart Brickenden, in the same quarry in Tilgate Forest from which 

 the earliest known tooth was obtained ; and subsequently a portion 

 of the upper jaw with teeth has been procured from the Hastings 

 strata. 



Referring to his various memoirs on the Iguanodon in the Philo- 

 sophical Transactions, and to his recent work on the Organic Re- 

 mains in the British Museum,* for details, the lecturer stated, that 

 while the compound structure of the lower jaw, and the mode of 

 dentition, established the reptilian character of the original animal, 

 the maxillary organs presented a nearer approach to those of certain 

 mammalia, than is observable in any other reptiles. The teeth in 

 the upper and lower jaw were arranged in a sub-alternate order as 

 in ruminants ; the face of the crown, or that having the thickest 

 coat of enamel, is placed mesially or on the inner side of the lower 

 teeth, and on the external surface of the upper. The anterior part 

 of the lower jaw is edentulous, and its symphisial extremity forms 



* " Petrifactions and their Teachings, or a Hand-book to the Gallery of 

 Organic Remains in the British Museum/' one vol. 1851, published by H, Gr. 

 Bohn. 



