THE IGUANODON AND H YLA20SAURUS. 
277 
collection which unquestionably belong to the pelvic region of some great Saurian, 
most probably of the Iguanodon, but at present all the elements of this part of the 
skeleton have not been found in a state suffieiently recognizable to admit of their 
positive identification. 
Caudal vertebrce . — The characters of the anterior caudals are so well known that it 
is unnecessary to describe them ; but on the somewhat angular caudals, originally 
referred by me to the Iguanodon, and subsequently ascribed to the Cetiosaurus by 
Professor Owen, and now restored to the former reptile by Dr. Melville, I will offer a 
few remarks. In the first place, in confirmation of the opinion that these vertebrae 
belong to the Iguanodon, I would especially call attention to the fact, that with the 
unquestionable Iguanodon sacrals found at Loxwood, and examined by Baron Cuvier 
(as previously mentioned, ante, p. 275), were several caudals belonging to the same 
individual, and these possess the angular form, and more or less grooved base, as may 
be seen by reference to the Geological Transactions, vol. ii. New Series, pi. 1.5. figs. 
1,3. I can vouch for the accuracy of the figures from having carefully examined 
the specimens at the time they were being drawn by that able artist, Mr. Scharf. 
I would next call attention to the spine of the Hylaeosaurus, which exhibits in the 
several modifications of its vertebrae, as great a discrepancy in the elements of the 
dorsal and caudal regions, as our proposed restoration of the spinal column of the 
Iguanodon. In the highly instructive specimen from the Weald of Sussex, represented 
on a small scale (one-sixth linear) in Plate XXXII. fig. 22, a nearly uninterrupted 
chain of vertebrae is preserved, commencing with the first caudals. The marked 
angular character of the middle and distal vertebrae is most obvious ; and the differ- 
ence between these bones and the anterior caudals, and the corresponding modifi- 
cations in the form of the chevron bones, are as great as those presented by the 
vertebrae we have ascribed to the different regions of the spine in the Iguanodon. 
If this chain of vertebrae of the Hylaeosaurus had not been found in connection with 
unquestionable bones of that reptile, namely, the dermal scutes and spines, no one 
could have established their relation ; and the tail of this Wealden reptile would have 
run the risk of being for ever separated from the body to which it originally belonged, 
and would probably have been honoured with a distinct generic appellation. 
The chevron bones in the Hylaeosaurus present a remarkable variation in form, as 
is shown in Plate XXXII. fig. 22. The most anterior (fig. 22 g) has a double head 
for articulation with the body of the vertebra ; in the next variety (fig. 22 f) the two 
articulating facets are confluent as in the Iguanodon ; in the distal (fig. 22 e) the 
chevron bones are so much elongated in a horizontal direction in a line with the axis 
of the body, as to be in contact with each other in the centre ; this part of the tail 
must therefore have formed a very strong elastic subcylindrical chain or chord. 
Pectoral arch . — I now arrive at the consideration of that part of the skeleton re- 
specting which, happily, no controversy can arise, and that has been established bv 
my own discoveries and investigations. By a reference to my former paper*, it 
* Philosophical Transactions, 1841, Plate VIII. fig. 19. 
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MDCCCXLIX. 
