ROOM III. TEETH OP THE IGUANODON. 235 



modified both in shape and arrangement in the different 

 genera. 



The form and disposition of the maxillary elements in the 

 Iguana are shown in Lign. 49 ; they are distinguished by 

 names which have reference to their office or situation, viz. 

 a, the dentary, supporting the teeth; b, the opercidar, or 

 splenial bone; c, the complementary, or coronoid ; d, the 

 surangular ; e, the angular ; and/* the articular bone, which 

 forms the upper and distal portion of the jaw, and includes the 

 depression for the reception of the condyloid end of the tym- 

 panic bone, or os quadratum. 



In the Crocodiles, Enaliosaurians, and other tribes of rep- 

 tiles, the elements of the lower jaw are greatly diversified, and 

 a knowledge of their characters is an important aid to the 

 palaeontologist in his attempts to ascertain the affinities of the 

 extinct saurians, fragments of whose maxillary organs are 

 oftentimes the sole indications that such types of animal 

 organization ever inhabited our planet. 



TEETH OF THE IGUANODON. Since the discovery of the 

 tooth which first apprised me of the occurrence of the remains 

 of gigantic herbivorous reptiles in the Wealdeii, I have col- 

 lected many hundred specimens of all sizes, and in various con- 

 ditions, from a minute perfect germ, to the worn-out crown of a 

 molar, ground down above by mastication, and reduced by 

 the upward pressure of a new tooth from beneath, to a mere 

 plate or disk of coarse dentine. In the collection purchased of 

 me by the Trustees of the British Museum in 

 1838, there were upwards of 150 teeth of the 

 Iguanodon, and among them were the most 

 illustrative specimens then discovered. I have 

 since obtained a few very instructive examples, 

 and some of my friends have good specimens 

 in their collections ; but, certainly, these teeth 

 have of late been less frequently met with 

 than formerly, and I believe the specimens in 

 the British Museum, and those in my private LIGH. so. TOOTH OP 

 coUection, comprise the most characteristic 

 forms hitherto observed. 



The perfect germ, and the unused tooth of 

 the Iguanodon, are characterised by the prismatic form of the 

 crown, the presence of from two to three or four longitudinal 



