many fragments of ribs, and a few with the spinal end entire the magnificent specimen on the shelf to the right of the group of caudal vertebræ, is the largest example of this part of the Iguanodon that has come under my observation. It was broken into numerous pieces in extracting the block of sandstone in which it was imbedded, and these were chiselled out singly, and connected together, and now form the finest bone of this kind collected in Tilgate Forest; though but a portion of the entire rib, it is forty-six inches in length, and five inches wide at its greatest breadth.' The ribs of the Iguanodon have very rarely been found in connexion with the vertebræ ; but the two-fold articulation of the costal processes by means of a tubercle and the head, as previously manifested in the structure of the anterior dorsal vertebræ, are characters which enable us to recognize the detached ribs of the gigantic herbivorous saurian. In the anterior ribs the head is large, and of an ovate form; the neck is very long, as may be seen in several of the specimens in the collection, decreases progressively in the middle region of the spine, and finally disappears: the posterior ribs being attached to the ends of the transverse processes. This construction of the costal elements corresponds with that of the crocodiles; in the lizards the attachment of the ribs to the vertebræ is by a single tubercle on the side of the body of the vertebra.

Sacral Vertebra.-The most important and novel feature in relation to the osteology of the Wealden reptiles enunciated in Professor Owen's Reports, was the remarkable structure of the Sacrum in the three extinct genera of Dinosaurians; namely, the Megalosaurus, Hylæosaurus, and Iguanodon; a character first observed in a fine specimen consisting of six vertebræ, with portions of the two iliac bones attached, in the interesting collection of W. D. Saull, Esq. of Aldersgate Street. No one had previously suspected that in these reptiles the pelvic arch was composed of more than two anchylosed vertebræ, as in the living Saurians (see ante p. 167), and that the neural arches were transposed from their usual place over the middle of the bodies of the vertebræ, to the ossified intervertebral spaces formed by the anchylosis of the "Fossils of Tilgate

1 Several portions of ribs are figured in my Forest," Pl. XI.

2 See "Reports on Brit. Foss. Reptiles," 1842, p. 105.

contiguous bones; the foramina for the transmission of the sacral nerves from the spinal chord, being situated above and behind the middle of the bodies.

Fragments of the pelvic arch, consisting of the centrum of one vertebra, with portions of others anchylosed to the articular ends, are not uncommon; and so long since as 1826, Sir Roderick Murchison transmitted to Baron Cuvier a specimen of this kind, found at Loxwood in Sussex,' with several lumbar and caudal vertebræ. Upon these bones M. Cuvier remarked, that the united bodies of the vertebræ 66 seem to indicate that the animal to which they belonged made such feeble use of its tail that the caudal vertebræ were occasionally anchylosed together." Even the magnificent specimen of the sacrum of the Megalosaurus, consisting of a series of five united vertebræ, figured and described by Dr. Buckland, in 1824, did not suggest the true structure of this part of the skeleton. The announcement of this fact was therefore to me of special interest, since it elucidated the nature of several fossils in my collection that were previously unintelligible.

With the view of acquiring an accurate idea of the vertebræ composing the sacrum of the Iguanodon, I obtained Mr. Saull's permission to have his unique and most instructive specimen completely developed at my own expense, as its characters were in some measure obscured by a layer of hard calcareous grit, with which, as is generally the case in the Isle of Wight Wealden bones, it was partially encrusted.3

This Fossil was obtained from the Wealden beds in Sandown Bay, and is strongly impregnated with oxide of iron, and traversed by veins of calcareous spar. It is the sacrum of a young animal, and consists of six anchylosed vertebræ (not

1 "Geological Transactions," vol. ii. (New Series), p. 105, Plate XV. figs. 4, 6.

2 On Baron Cuvier's last visit to England, in 1830, I showed him some vertebræ anchylosed in like manner, and on which he made the same remark.

3 The specimen is figured (for the first time) in Pl. XXVI. of my "Memoir on the Iguanodon, Phil. Trans." 1849. As Mr. Saull, with great liberality, throws his museum open to visitors every Thursday after mid-day, this unique fossil can be seen by any person interested in this department of Paleontology.

of five as described in "Brit. Foss. Reptiles," p. 130), with the right iliac bone attached. The relative size and proportions of the several bones composing the sacral arch are now well displayed. The body of the first or anterior vertebra is large, strong, and expanded, forming a powerful buttress in front; the bodies of the two posterior vertebræ are likewise large and strong; but the second, third, and fourth, are constricted laterally in the middle, and 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.1 A similar conformation is observable 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 vertebræ have the same relative proportions.2 The only portion of the sacrum of the Iguanodon in the British Museum, is the detached vertebra placed above the tray containing the femur marked No. 5, in the upper division of Wall-case C. (See diagram, ante, p. 227. 2.) It evidently belonged to a young individual, for the body has separated from the contiguous bones without fracture.

THE PELVIS.-ILIUM.-Of the bones of the pelvis, namely the Ilium, Ischium, and Pubis, specimens of the first only have been found in connexion with the sacrum, or associated with other parts of the skeleton. The right and left iliac bones, detached from the pelvic arch, are imbedded near each other, in the Maidstone fossil; and in Mr. Saull's, a considerable portion of the right ilium remains attached in its natural position.3 Captain Lambart Brickenden has the finest detached example of this element of the pelvis that has

A detailed anatomical description of this sacrum is given in" Philos. Trans." 1849, pp. 297-299.

2 Among the water-worn masses of bone strewn along those parts of the southern shores of the Isle of Wight, which are bounded by cliffs of the Wealden strata, I had often met with specimens in which the body of a very large vertebra was anchylosed to one so disproportionately small, that I could not explain their origin, until Professor Owen's description of the structure of the sacrum suggested their true nature. These fossils in fact consist of one of the large bones either of the anterior or posterior end of the sacrum united to one of the slender middle vertebrae.

3 “ Philos. Trans." 1849, Pl. XXVI. A.

come under my observation; it was found imbedded in the friable sandstone of Tilgate Forest, from which it has been successfully extricated.

The ilium of the Iguanodon resembles that of the monitors in its hatchet-like form, and in the prolonged extremity; in the Maidstone specimen one of the iliac bones shows the inner or sacral surface, and the other the outer aspect. The slender prolonged extremity described by Professor Owen as the posterior part, is regarded by Professor Melville as the anterior, and "only an exaggerated condition of the short spine projecting forwards from the ilium in the smaller lacertæ." The discovery of perfect specimens of the bone, or characteristic portions in connexion with the sacrum, will determine this question that the anterior part of the sacrum is that so described by Dr. Melville in the "Philosophical Transactions," is confirmed by the specimens subsequently obtained.

OS PUBIS. Wall-case C, uppermost shelf. (Diagram, ante, p. 227.)-A fragment of a very broad and curved plate of bone, (labelled 2132), 16 inches long, and 9 wide, and but 3 inches in its greatest thickness, and which required many hours of labour to extricate from the stone in which it was imbedded, is evidently a portion of the pubis of a gigantic saurian; it is, with great probability, ascribed to the Iguanodon by Professor Owen, who thus describes it. "The Pubis, which presents a simple spatulate form in the Crocodiles, already begins to increase in breadth at its symphysial extremity in the extinct family with concave vertebræ; and in the larger existing species of Lizards is expanded at both extremities, and has a very marked and recognisable character superadded, in being bent outwards with a considerable curvature.

"A massive fragment of a broad osseous plate, bearing a segment of a large articular cavity at its thickest margin, and thence extended as a thinner plate, bent with a bold curvature, and terminated by a thick rounded labrum, offers characters of the Lacertian type of the pubis too obvious to be mistaken; and since the modifications of the ilium of the Iguanodon in the Maidstone skeleton approximate to the Lacertian type of the bone, and especially as manifested by the great Varani, in which the recurved character of the pubic plate is most strongly marked, we may with much

probability, assign the fossil in question to the pelvis of the Iguanodon.

"This fine portion of pubis is of an inequilateral triangular form, 16 inches in its longest diameter, 93 inches across its base, or broadest part, 6 inches across its narrowest part. The fractured surface of the bone near the acetabulum, is 3 inches thick. The acetabular depression is seven inches across, a proportion which corresponds with that of the acetabular concavity in the ilium, and with the size of the cavity in which the head of the Iguanodon's femur must have been received. One angle of the cavity corresponding with the anterior one in the Varanus, is raised; a broad and low obtuse ridge bounds the rest of the free margin of the cavity. The smooth labrum exchanges its character near one of the fractured edges of the bone for a rough surface, which indicates the commencement of the symphysis. In the apparent absence of the perforation below the acetabular depression, the present bone agrees with the Crocodilian type."-Brit. Assoc. Rep. 1841, p. 136.

ISCHIUM? Wall-case C. Upper shelf.-Near the specimen last described, there is a fragment of a large lamelliform bone, (labelled), which Professor Owen considers to bear most resemblance in its general form and slightly twisted character to the Ischium, with traceable modifications intermediate to those presented by the extinct Goniopholis, and modern Varani and Iguance. I had often attempted to discover the true character of this bone when in my possession, but could not arrive at any satisfactory conclusion respecting it; it struck me as more nearly resembling a bone of the arm than of the pelvis, and that it might possibly be the humerus of an unknown species or genus of saurians; its surface and texture differ from those of the bones of the Iguanodon.

CAUDAL VERTEBRÆ AND HÆMAPOPHYSES. Wall-case C, lowest compartment. These elements of the spinal column have been discovered from time to time in numerous localities of the Wealden strata; the caudal vertebræ collected by myself, or submitted to my examination, amount to several hundred specimens. The most splendid example beyond comparison is the series of six anterior caudal vertebræ with their processes almost entire, and three chevron-bones or hæmapophyses,