ROOM III. UPPER TEETH OF THE IGUANODOX. 253 



aspect. Expansions of the alveolar septa on each side are 

 adapted to the lateral planes of the fang, and the inner 

 parapet is deficient opposite the triangular tract above-men- 

 tioned, but is closed below, and separates the alveolus from 

 the cavity of reserve in the secondary dental groove. 



The teeth never become anchylosed to the sockets; the 

 great transverse diameter of the dentary element of the jaw 

 above appears to have allowed of the outward curvature of 

 the elongating fang, while the inner surface was maintained 

 nearly vertical. By the same provision the germ attained a 

 considerable size before it pressed upon and excavated the 

 root of the tooth it was destined ultimately to displace. 

 The wedge-shaped crown and the anterior serrated recurved 

 trenchant edge, must have rendered the teeth in this early 

 stage very efficient instruments, in the absence of incisors, 

 for cutting vegetable food. 



The arrangement of the upper and lower molars, and the 

 situation of a lower successional germ, are shown in Lign. 

 56, in which two upper molars of the right side are repre- 

 sented on their external or enamelled aspect, and a corre- 

 sponding lower molar beneath them : in jig. 2, are shown the 

 opposite or internal aspect, and the position of a successional 

 germ in the fang of the lower tooth, fig. 4. 



Teeth of the Upper Jaw. Lign. 56, 1, 3. After the 

 determination of the form and position of the teeth of the 

 lower jaw, the next question to be determined was, whether 

 the teeth in the upper maxilla had the same shape and cur- 

 vature as those of the lower. Upon examining the extensive 

 series in the British Museum, several teeth were found dif- 

 fering in shape from the now-ascertained type of the lower 

 molars of the Iguauodon; these, however, so closely corre- 

 spond in all essential respects, that no reasonable doubt can 

 exist of their having belonged to the upper jaw of the same 

 species of reptile. From the mutual adaptation of the grind- 

 ing surfaces, and the situation of the excavation produced 

 by the replacing germ which in all analogous cases is in the 

 mesial aspect of the fang the inference was obvious that 

 these teeth not only did belong to the upper series, but that 

 they were curved in an opposite direction to those of the 

 lower; namely, with the convexity external, and the con- 

 cavity internal; the hollow for the successional germ being 



