WEALDEN FORMATIONS. 27 



pact bone from three to four lines in thickness, forming the outer surface, b, b, and a 

 similar la) T er from one to two lines thick, forming the inner surface, i, and increasing to 

 near three lines in thickness, where it bends down to form the shallow inner boundary of 

 the alveolar groove, ?, a ; the compact substance is not continued over the alveolar groove 

 itself; the intermediate substance is an areolar osseous tissue, the meshes being most 

 open along the inner and upper surface of the bone. The maxillary canal, c, exposed in 

 this section is nearer the outer surface ; it measures 14 lines by 8 lines in its diameters, 

 sending off branches which perforate obliquely, outwards and forwards, the compact 

 outer wall of the jaw. Of the three oval nervo-vascular foramina, g, g, preserved in the 

 present fragment upon the outer surface, two are 4 lines, and the third 3 lines in long- 

 diameter ; they are included in a space of 16 lines, are situate about an inch above the 

 worn outer border of the alveolar groove, and are the last three of the series of such 

 foramina. They correspond nearly in size and relative distance from the alveolar 

 border with those at the back part of the similar series of nervo-vascular foramina in 

 the lower jaw of the Iguanodon ; and like them the obliquity of their course indicates 

 the relation of the fragment to the anterior and posterior extremities of the jaw. The 

 corresponding foramina are present on the same part of the bone in the more mutilated 

 homologous portion of a dentigerous bone of the Iguanodon figured in Dr. Mantell's 

 ' Memoir,' above quoted, PI. XIX, and equally prove the part to which those orifices 

 incline as they open outwards to be the anterior end of the fragment, and not the 

 posterior end, as the anatomist conjectured of whose aid Dr. Mantell availed himself 

 in the interpretation of this fragment. 



The vertical extent of the slightly convex outer surface of the maxillary, in front 

 of the malar process, in the present fragment, is 3 inches, but a portion has been broken 

 away from the border, to which the smooth and flat inner surface of the maxillary 

 converges as it ascends ; it is possible, therefore, that the outer wall of the maxillary 

 of the Iguanodon may have been continued relatively as high vertically as in the 

 Iguana, Varanus, Tejus, and most other Lizards: anterior to this broken upper surface 

 is a portion of a wide smooth depression, or of a canal laid open. 



The alveolar groove, as it extends backwards, curves outwards, in the same degree 

 as the alveolar groove does at the same part in the lower jaw, Tab. XII, fig. 3. The 

 extent of the alveolar groove in the present fragment of the upper jaw is 8 inches ; the 

 antero-posterior diameter of the crown of the largest tooth is 1 inch ; it seems to 

 answer, therefore, to the posterior half of the dentary part of the lower jaw of the 

 Iguanodon. The first tooth, i, is a fully developed or old one, with its cement-covered 

 base apparently continuous or confluent with the cancellous bottom of the groove, «'. The 

 crown of the tooth, 2, which is about to succeed it, and which has in part undermined and 

 excavated the old tooth, is on the inner and posterior side of its base ; the crown of 

 the new tooth is widely and deeply excavated, as shown in the section, fig. 4, % where 

 the hollow base of the crown has suffered a slight fracture and displacement : 



