﻿2 



FOSSIL REPTILIA OP THE 



3 lines in the same dimensions. The crown-germs of the teeth in the Stammerham 

 jaw (ib., ib., PI. XI) average 6 lines ; we thus learn that each successive series 

 of teeth had an increase of size corresponding in a general degree with the growth 

 of the jaw. 



The subject of fig. 1, PI. I, of the present Monograph shows at its interior or 

 symphysial end the abrupt slope downward of the short, edentulous, compressed part, 

 which curves inward to meet the corresponding part of the opposite ramus at a short 

 symphysis, extending along an horizontal surface, parallel with the straight lower border 

 of the mandible. The smooth canal thus formed above the symphysis indicates a relation 

 of facility in regard to the movements of protrusion and retraction of a long, cylindrical, 

 muscular tongue, probably used, like that of the Giraffe and Megatherium, for the pre- 

 hension of the vegetable substances selected by the Iguanodon for food. It is a generic 

 mandibular character. 



The commencement of the coronoid process, contributed by the dentary, is the same 

 in extent as that shown in the younger Iguanodon's jaw (ib., ib., PL XI, a, /), and 

 indicates the position of the suture of the dentary with the surangular element. 



The surface of the tooth-crowns here exposed shows the submedian primary vertical 

 ridge, which, in detached teeth, indicates the hinder border of the crown by its proximity 

 thereto. The secondary ridge is less strongly marked, and is best shown in the hindmost 

 teeth. The anterior lamello-serrate border describes the usual convex curve ; the 

 posterior border being almost straight along its chief extent. The dental characteristics 

 of Iguanodon Mantelli, as illustrated in previous plates (ib., ib., PI. XVIII, Supplement, 

 No. Ill, ' Iguanodon/ PI. X), 1 are well maintained. The secondary ridge is, however, 

 less developed than in the larger teeth of older Iguanodons. The alveolar border here, 

 as in the smaller jaw (PI. XII, fig. 3), describes a gentle sigmoid curve in the transverse 

 direction, the convexity being inward in the hinder two thirds, then straight or slightly 

 concave to the commencement of the symphysial slope. Three generations of teeth, a, b, 

 c, are exposed in the present mandibular fossil (PI. I). 



In the inwardly convex part of the alveolar tract the teeth are placed ' en echellon 

 the fore-and-aft plane of the anterior tooth (PI. I, fig. 1 h), if carried back, would pass 

 outside the succeeding tooth, and the crown of this stands in like relation to the next 

 tooth behind. Thus, when fully in place, the crowns slightly overlap in the lower as 

 in the upper jaw {' Monograph on Iguanodon,' Part No. I, Plate XI, fig. 2), 2 

 and eighteen teeth may range along an alveolar tract, which, if each tooth stood 

 clear of the next, would not support more than fourteen. Room is also got for the full 

 number along the working line by a certain alternation in the degree of attrition, as is 

 well exemplified in the portion of mandible of a younger or smaller Iguanodon next to be 

 described (PI. I, fig. 8). 



Three views of an upper tooth (PI. I, figs. 2, 3, 4) and three views of a lower tooth 

 1 Pal. Soc. Vol. for year 1862. 2 Ibid. 1854. 



