28 FOSSIL REPTILIA OF THE 



portion of the upper jaw (Tab. VII, figs. 1, 2, and 3, m) has its summit obliquely 

 worn from above downward and outward to the enamelled trenchant border ; the 

 contiguous tooth, n, the summit of which has not suffered abrasion, is pressing 

 upon the smooth, concave side of the older tooth; a third tooth, , the crown of 

 which is still buried in the alveolus, has the same relation to the more advanced 

 tooth, n. The smooth, concave sides of these teeth, shown in fig. I, are, therefore, 

 the inner or mesial ones, and the flat surface of bone extending from the alveolar 

 border is the inner or palatal alveolar wall of the maxillary bone. 



The crown of each tooth shows that more definite and prominent primary 

 ridge on their outer side {a, figs. 2, 3, and 4) which is characteristic of the teeth 

 of the upper jaw of the Iguanodon. 



In figs. 5 and 6, three of the teeth ( m, n, o) show precisely the same stages of 

 growth as the foregoing one; one (m) has the summit abraded from the enamelled 

 trenchant border downward and outward ; in a second (n) the crown is extri- 

 cated, but not worn ; in a third (o) the major part of the crown is still in the 

 formative cell. The relative position of these three teeth to each other is, in one 

 respect, the reverse of those in fig. 1. The convex ridge side of the crown of 

 the second tooth (fig. 5, ?>) partly overlaps (instead of being overlapped by) that 

 of the first (»*), and it is similarly overlapped by the germ of the third (o). 

 The side of the jaw to which the newer teeth {a r, fig. 5) are nearest is the 

 inner one ; the smooth, longitudinally concave, side of the tooth is next the outer 

 side of the jaw (fig. G) ; they belong to the lower jaw, and they show the formal 

 characters of mandibular teeth ; the primary ridge, a, is less produced. 



The upper teeth (figs. 1 — 4) are narrower, in the direction of the length of the 

 jaw, or from c to d, and are less curved than the lower ; the fang and base of the 

 crown are thicker, transversely to the jaw or from a to g (fig. 4). The primary 

 ridge, a, is more prominent ; the secondary ridges, b, are less constant and less 

 marked than in the lower teeth. Both fore (c) and hind (d) borders at the 

 base of the crown are entire, and are bent or produced slightly outward, bound- 

 ing the transversely concave areae between them and the primary ridge ; they 

 slightly diverge as the crown expands; along its apical half both borders are serrate 

 or serro-lamellate, converge, and, with a slight difference of contour, meet at the 

 apex of the unworn crown formed by the termination of the primary ridge (w o, fig. 2). 

 This ridge, a, commencing in a tooth 3J inches long about 1 inch 8 lines from the 

 base, becomes thinner and sharper as it projects, which is to the greatest degree 

 before it reaches the middle of the crown, whence it gradually subsides to the 

 apex ; its longitudinal profile is a slight curve convex outward : this ridge 

 divides the outer side of the crown unequally, the front area, a, c, being broader, 

 sometimes nearly twice the extent of the hind one, a, d. The dentated margin of 

 the crown to which the primary ridge is the nearest is the posterior one, and is 



