190 
DR. MANTELL ON THE IGUANODON. 
abbreviated proportions of the short blunt-headed lizards as the scale — as for ex- 
ample the Chameleons — the length of the jaw of this Iguanodon must have exceeded 
three feet. 
I will now describe the portion of a left upper maxilla in the British Museum, 
which corresponds so perfectly in its general characters with the lower jaw, as to 
leave not the slightest doubt of its having belonged to the Iguanodon, although no 
teeth remain to establish the identity. 
Portion of the Upper Jaw, Plate XIX. figs. 1, 2*. — This specimen consists of the 
anterior part of the left maxillary bone, having on the under surface (fig. 1) the 
alveolar furrow with the bases of the sockets of ten teeth ; and on the upper (fig. 2), 
the deep channels of the infra-orbital vessels and nerves that supplied the teeth and 
integuments of the front of the jaw and face on the left side : this fossil is represented 
of the natural size. Dr. Melville, who has most kindly aided me by his profound 
anatomical knowledge throughout this investigation, and liberally devoted much 
time and attention in instituting the necessary comparisons between my specimens 
and those formerly collected by m.e, and now in the British Museum, with the jaws 
and teeth of recent reptiles, has favoured me with the following observations on this 
subject. 
“ This fragment of the left maxilla, which is eight inches five lines long, and two 
inches seven lines broad, formed the lower boundary of the nasal surface ; it is 
broken off where the vertical parapet rises to enclose the olfactory fossa. The cor- 
responding part in the skull of an Iguana (/. tuherculata) , measuring four inches two 
lines in length, is six lines long, or nearly one-eighth that of the cranium ; this ratio 
gives five feet four inches as the length of the skull of the Iguanodon to which the 
fossil belonged ; but as the brain and the organs of sense would have a less propor- 
tion to the whole bulk in these gigantic Saurians than in the small species of existing 
Lizards, we may infer a diminution in the absolute size of the head, corresponding 
with the abbreviation and contraction of the cranium ; and the length in the adult 
would probably average about four feet. 
^‘ Phe breadth of the fragment continues uniform ; in front it is rounded olf exter- 
nally (x), and exhibits the oblong terminal irregular surface for articulation with the 
intermaxillary bone by which it was overlapt. The large infra-orbital canal (fig. 2, a, a) 
opens at tlie junction of the posterior and middle third, and midway between its 
margins ; passing into a broad and deep sigmoid groove which curves inwards as it 
advances so as nearly to reach the inner edge in the centre of its course, where it gives 
off a retrograde furrow extending over the internal margin (fig. 2, b). In front it is 
deflected outwards, extending along the posterior border of the intermaxillary 
* I discovered this fossil in 1838, in a quarry near Cuckfield, and it was labelled in my Catalogue “fragment 
of the upper jaw of an Iguanodon.” By the kind permission of Mr. Konig, the specimen has recently been 
cleared of the sandstone with which it was partially invested, so as to expose its peculiar characters as repre- 
sented in Plate XIX. 
