136 
DR. MANTELL ON A PORTION OF THE LOWER JAW 
Tympanic bone. — Of this bone, which in the Iguana and other reptiles is largely de- 
veloped, and forms the articulation between the skull and the lower jaw, several ex- 
amples are preserved. One specimen is seven inches in length, exceeding by fourteen 
times in linear dimensions the corresponding bone of the Iguana ; and there are frag- 
ments indicating much larger proportions. These bones are figured and described in 
the ‘Geology of the South-East of England* * * § .’ The body of the bone constituted a 
strong vertical pillar, having two unequal lateral processes ; its walls are extremely 
thin, and the auditory cells, with which it is traversed, are very large. 
Hyoid apparatus. — A bone resembling a lateral appendage of an os hyoides of the 
lacertian type, was discovered in a block of stone, associated with bones of the Igua- 
nodon ; but it was broken to pieces in the attempt to extricate it from the rock, and 
its characters could not be determined. 
Horn of the Iguanodon (Plate IX. fig. 2.). — Before proceeding to the consideration 
of the bones of the trunk and extremities, I would call attention to the remarkable 
osseous appendage which I discovered many years since in a quarry near Cuckfield, 
imbedded in a mass of stone containing bones of the Iguanodomf-. This horn, or nasal 
tubercle, so closely resembles in form and structure the processes on the front of the 
Iguana cornuta (Plate IX. fig. 3.), that there can be no doubt it occupied a similar 
position on the skull of some one of the colossal reptiles of the Wealden, most pro- 
bably of the Iguanodon. 
Vertebral column. — About fifty plano-concave vertebrae in the collection in the 
British Museum may probably be referred to the Iguanodon, so far as separate verte- 
brae can be identified by comparing them with those in the Maidstone specimen, or 
with vertebrae which have been found associated with other parts of the skeleton. 
But the promiscuous manner in which detached parts of the vertebral columns of se- 
veral genera of Saurians are intermingled in the strata of the Wealden, and the 
mutilated condition in which they commonly occur, render it necessary to institute 
a rigorous examination of the entire collection before conclusive identities can be 
established. In this brief notice I shall refer only to some of the most remarkable 
specimens, in the hope of directing attention to the subject. The usual characters of 
the dorsal and caudal vertebrae of the Iguanodon have been pointed out in my former 
works and a remarkable series of, probably, the first six caudal, with their processes 
almost entire, supplies us with the elements of that part of the spinal column §, as is 
shown in the annexed sketch, Plate VIII. figs. 24, 25, and Plate IX. fig. 9. 
a a. Body of the vertebra : the anterior surface of the centrum is depressed, 
and the posterior surface nearly flat. 
* Plate ii. fig. 5. 
f Geology of the South-East of England, plate iii. fig. 5. 
I The Fossils of Tilgate Forest, and the Geology of the South-East of England. 
§ This specimen, which was collected by R. Trotter, Esq. F.G.S., is figured, ‘Wonders of Geology,’ vol. i. 
plate iii. fig. 8. (4th edition.) 
