276 
DR. MANTELL ON THE OSTEOLOGY OF 
are more slender than either the anterior or posterior ; by this modification of the 
elements of the sacral arch, both lightness and strength were obtained. 
A similar construction is present in every specimen of the sacrum that has come 
under my observation, whether of young and small, or of old and large individuals ; 
in all, the same relative proportions in the size of the vertebrae are present, as in 
Mr. Saull’s fossil. 
A portion of the sacrum of a young Dinosaurian consisting of four vertebrae, — the 
two posterior and two of the middle series — recently discovered in Tilgate Forestand 
presented to me by Captain Lambart Brickenden, is represented of the natural 
size in Plate XXVII. This fossil beautifully exhibits the forms of the bodies of the 
vertebrae, and the attachment of the neural arches to the anchylosed intervertebral 
spaces. The vertebrae differ so much in iheir proportions and configuration from 
those in the fossil figured in Plate XXVI., as to render it doubtful whether this 
specimen may not be a portion of the sacral arch of the Hylaeosaurus : this subject 
will be more fully considered by Dr. Melville in the subjoined report*. 
Another highly interesting series of the sacral vertebrae, with four consecutive an- 
terior caudals of the same reptile, found by Peter Martin, Esq., at Charlwood in 
Surrey, are figured in Plate XXX. figs. 15, 16, 17, one-fourth the natural size. The 
portions of the sacrum consist of the anterior, three middle, and one of the posterior 
vertebrae, all of which are more or less mutilated (Plate XXX. figs. 15, 16). The im- 
plantation of the neural arches in the intervertebral spaces, the coalescence of the 
expansion above, and the foramina for the transit of the sacral nerves (fig. ] 5, z), are 
well shown : and the relative size of the last sacral and first caudals is seen in the 
series of four anterior caudal vertebrae (fig. 17). The absence of a chevron bone at 
the junction of the two first caudals (fig. \7,x), and the presence of this element in 
the succeeding interspaces (fig. 17 , b *, *), seem to indicate that the first of this series is 
the second caudal; as the deep concavity of the posterior anchylosed sacral vertebra 
renders it probable that the anterior face of the first caudal — the bone which unites 
the tail to the pelvis — was more or less convex ; as is the case in the Crocodile, 
Gavial, Scc.-f- 
Pelvis. — Of the pelvic bones, the Iliac, of which both the right and left are pre- 
served in the Maidstone specimen, and the right Ilium in the sacrum figured in 
Plate XXVI., are alone determined. There are portions of large bones in my former 
* Among the water- worn masses of bone so abundantly strewn along those parts of the southern shores of 
the Isle of Wight, which are bounded by clilFs of the Wealden strata, I had often met with specimens in 
which the body of a very large vertebra is anchylosed to one so disproportionately small, that I could not ex- 
plain their origin, until Professor Owen’s description of the structure of the sacrum suggested their true nature. 
These fossils are in fact one of the large vertebrae either of the anterior or posterior end of the sacrum united to 
one of the slender middle vertebrae. A specimen of this kind in the highly interesting collection of Mr. Baber, 
is of enormous size ; the anterior face of the largest vertebra being inches by 6 ^ in diameter. This fossil is 
also interesting on another account, for on one side of the body of the largest vertebra there is an abnormal 
enlargement (or exostosis) : I have observed similar bony tumours on the sides of the bodies of other vertebrae. 
t See Wonders of Geology, sixth edition, p. 419. 
