194 
DR. MANTELL ON THE IGUANODON. 
Teeth of the Upper Jaw, Plate XVIIL figs, 1, 2. — After Xylograph, No. 5. 
the determination of the form and position of the teeth of 
the lower jaw, yielded by the instructive specimen previously 
described, 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 Iguanodon. These are, however, in all essential 
respects so analogous to the inferior teeth, that no reasonable 
doubt can exist of their having belonged to the upper jaw 
of this reptile. From the mutual adaptation of the grinding- 
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 concavity in- 
ternal ; the hollow for the successional germ being situated in 
the latter (Plate XVIII. fig. Thus the upper and lower 
molars were related to each other nearly as in the Ruminants ; 
the outer aspect below corresponding to the inner above ; the 
triturating’ facet inclining from above downwards and out- 
^ ^ View in profile of an upper and lower 
wards in the inferior series, and from below upwards and moiar, of the left side, 
inwards in the superior ; in the lower teeth the enamelled edge is within and the 
most elevated, while in the upper it is external and inferior. The annexed diagram 
(Xylograph, No. 5) of an upper and lower tooth, seen in profile, explains this 
arrangement. 
‘‘ By this adjustment the hard unvascular dentine with its coating of enamel, 
played on the softer vaso-dentinal tract of the tooth opposed to it below ; and a 
bevelled or chisel- like surface was maintained for triturating the food when drawn 
into the mouth by the large prehensile tongue, which is indicated by the procumbent 
and inferiorly excavated symphysis. The upper molar is also distinguished by the 
smaller antero-posterior diameter of the crown — by the great prominence of the pri- 
mary ridge {n) — by the breadth of the vertically convex surface of the fang — by the 
width of the lateral facets — and by the contraction of the internal or vertically con- 
cave surface which becomes ridge-like below. 
‘'The anterior and inferior serrated edge is rapidly recurved towards the blunt 
excentric apex, and forms above an obtuse prominent angle with the upper segment 
of that border, which is striated, and everted as it were by the encroachment of the 
anterior deeply concave lanceolate facet impressing the lower portion of the crown 
