20 FOSSIL REPTILIA OF THE 



counting from before backward. Each of these germ-teeth has the inner surface 

 exposed of the summit of the crown, the anterior one showing the least proportion 

 of the tooth. The primary longitudinal ridge (fig. 5, a) and the marginal serra- 

 tions [cc') are boldly and beautifully marked on the dark, lustrous enamel, the 

 serrations being continued by grooves, some way upon the exposed inner side of 

 the crown. The primary ridge more equally divides the summit of the crown 

 here seen than in the part below, but the greater extent of the anterior area (c) is 

 appreciable ; the secondary longitudinal ridge {h) is discernible in both the anterior 

 and posterior areaj of the crown, in the last two germs (fig. 1, I2, 14, and fig. 6. So 

 much of the crown as appears in these teeth shows greater fore-and-aft breadth than 

 the socket they would rise into, or rather than the socket of their predecessor, and 

 the difference of breadth is so much greater in the basal part of the crown as to 

 suggest much growth of the jaNv in the progress of the germ to the state of a fully 

 developed tooth in place. We thus obtain evidence of the immaturity of the 

 specimen, and that it has not belonged to a distinct and diminutive species of 

 Iguanodon. 



Like all reptiles, the Iguanodon shed and renewed its teeth many times during 

 the course of lifcj the new following the old teeth vertically, and being, therefore, 

 in the growing animal, of a larger size than those they were about to displace. 

 With the shedding of the deciduous teeth there was more or less absorption of 

 their sockets, and with the rise of the successional teeth there was a concomitant 

 formation of suitable, and, therefore, larger sockets. 



In the Crocodile the number of teeth, or of sockets of one and the same set of 

 teeth, does not vary with age, according to the observations of Cuvier,* Each 

 tooth succeeds its forebear vertically, and none are added to the series, as in 

 mammalia, from behind. 



I believe myself able now to adduce evidence that the Iguanodon added this 

 mammalian mode of succession to some other characters, which have been in pre- 

 vious Monographs pointed out, exemplifying its greater resemblance to the 

 warm-blooded beasts than any existing form of reptile manifests. 



The mandible of the young Iguanodon here described shows at the utmost 

 fifteen sockets in the unquestionably entire series, occupying a longitudinal extent 

 of four inches and a quarter. The mandible of the somewhat older Iguanodon, 

 from the Wealden of Stammerham, Sussex, described and figured in my Mono- 

 graph, 1S55, Tabs, X and XI, shows eighteen alveoli, occupying a longitudinal 

 extent of six inches. 



* " Les dents offrent plusieurs remarques interessantes dans le crocodile. La premiere, c'est que leur 

 nombre ne change point avec I'age. Le crocodile qui sort de I'ocuf les a autant que celui de vingt pieds de 

 long." — " Je me suis assure de ce fait dans uue scrie de huit tetes croissant en grandeur, depuis un pouce 

 jusqu'a deux pieds." Cuvier, ' Ossemens Fossiles,' 4to, torn, v, pt. ii (1825), p. 90. 



