in such collocation with other well-determined bones and vertebræ of the Iguanodon, as to leave no reasonable doubt of their belonging to that animal.

5thly, The number of these vertebræ of different ages and sizes in our collections is such as we might have expected on that supposition ; and

6thly, if these be not the cervical vertebræ of the Iguanodon, we have the (assumed) Streptospondylus major with nothing but a neck, whilst the Iguanodon, as yet known, is wholly destitute of that region of the spine. Is it not, therefore, more probable that the neck of the so-called Streptospondylus belongs of right to the Iguanodon, especially as the bones of that reptile, tested by the fortunate discovery of the Maidstone specimen, constitute the great majority of the osseous relics from the deposits of the Weald?-in other words, the Iguanodon is the reptile par excellence characteristic of the Wealden formation.

"The Streptospondylian form of the body of a vertebra can no more characterize a genus of Reptiles than the amphicœlian or cœlospondylian modifications; each is common to a group of species constituting not only distinct genera and families, but also orders and subclasses. Nay, the Streptospondylian type is not even persistent throughout the elements of the same spinal column; it disappears towards the middle of the dorsal region in the Steneosaurus rostro-minor, the best known example of this structure, and that in which it was first recognized by Baron Cuvier. The genus Streptospondylus of V. Meyer ought therefore to be abolished, and the residual generic application Steneosaurus (G. St. Hilaire) be retained to designate Cuvier's first Gavial of Honfleur. The amphicœlian and procœlian forms are generally continued through the whole length of the vertebral column; the Streptospondylian modification in the last sacral replaces, and in the first caudal is superadded to, the procœlian form of the vertebral bodies characteristic of the living Crocodiles.

"In the Report on British Reptiles much stress is laid on the uniformity in length of the bodies of the same vertebral series in Reptiles; this indeed holds good within certain limits among the less complicated smaller existing Lacertæ, but will lead us into error if rigidly applied to the more highly organized extinct Saurians and Crocodiles. The rela

tive length of a vertebra must always be taken exclusively of the articular convexity, whether that be in front or behind, as is the practice in stating the absolute length of the spine or of its individual regions. Deterred by the great length of the cervical vertebræ referred to the Streptospondylus major, when compared with the shortness of the dorsal or lumbar vertebræ assigned by him to the Cetiosaurus brevis, Professor Owen was unwilling to associate them together as belonging to the spinal column of the same species of reptile, which, however, appears to be really the case, as I shall afterwards have occasion to demonstrate." 991

If Professor Owen's opinion be correct, and the bones in question belong to the Streptospondylus, then the vertebræ composing the neck of the Iguanodon are at present unknown.

The only specimen that appears to me to afford conclusive evidence on this question is in the possession of J. S. Bowerbank, Esq. F.R.S., and consists of a considerable portion of the spinal column of a very young Iguanodon, imbedded in calciferous grit. Found with this fossil, but detached from it, and without any indication of its connexion with the spine, to which, I believe, it unquestionably belongs, is a series of three cervical vertebræ, which, with his characteristic liberality, Mr. Bowerbank allowed me to figure in illustration of my fourth Memoir on the Iguanodon, in "Philos. Trans.," 1849. Pl. XXIX. fig. 9.

These vertebræ are especially instructive because they demonstrate the true characters of the bones of the neck in a very young Iguanodon; for it is to this reptile this vertebral column must be ascribed. Unfortunately, the bodies of the vertebræ have been crushed and compressed almost flat laterally, and the natural form of the inferior part of the centrum is destroyed, the visceral aspect presenting a sharp ridge, and thus assuming a different contour to that of an adult cervical in my cabinet, which has been compressed in an opposite direction. Nevertheless, the close analogy between these vertebræ is sufficiently obvious; the structure of

'In confirmation of the remarks of Professor Melville, I may add that among the large convexo-concave saurian vertebræ recently obtained from the strata of Tilgate Forest, are cervicals and dorsals, belonging to two, if not three, distinct generic types.

the neural arch is identical; and the only essential difference between the bodies of the respective vertebræ is, that the anterior articulating facet is less convex in the young reptile than in the adult; but as the posterior articular end of the centrum is deeply concave, it is probable that in the recent state the anterior facet possessed a cartilaginous convex epiphysis, by which the ball-and-socket joint was completed: as in the skeleton of the young Gavial the facets of the sacrococcygeal vertebra are flat, though very convex in the adult; (ante, p. 167.) so in the Iguanodon, the ball and socket of the cervicals may not have been fully developed and ossified till the reptile arrived at maturity.

The detached neural arch of a small cervical vertebra on the shelf on the extreme left of Wall-case C, merits notice, because I submitted it to the examination of Baron Cuvier in 1830, who expressed his belief that it was the axis of a young Iguanodon. The bone was then imbedded in a block of Tilgate grit, and the cast of the spinal canal in calcareous spar was visible, resembling the prolongation of the medulla oblongata the surrounding stone has since been removed, and the fossil proves to be the neural arch of a cervical vertebra-probably, of a crocodilian reptile.

DORSAL VERTEBRÆ.-Wall-case C, lowest compartment.—As the anterior dorsal vertebræ have not been found in juxtaposition with other known parts of the skeleton, our knowledge of this region of the spinal column is scarcely more definite than that of the cervical. A large convexo-concave anterior dorsal in my possession, is figured and described by Dr. Melville ("Philos. Trans.," 1849, p. 284, Pl. XXVIII.) as a vertebra of the Iguanodon; and if that accurate observer's reference of the cervicals proves to be correct, there can be no doubt that the dorsal in question belongs to a reptile of the same genus. Although there are no vertebræ of this type in the Museum, yet the following notes may be useful to the anatomical inquirer :

"The anterior convexity is much less than in the cervical, and the posterior concavity shallower; the section of the body would present a deep triangular outline, with the apex below, corresponding to a thick median crest. The body is contracted in the centre, so that the sides are concave parallel to its axis, but convex vertically, owing to the great

prominence of a broad longitudinal ridge, equivalent to that bearing the parapophysial surface in the cervical, above and below which there is a deep concavity. The spinal canal has a transversely oval outline, and enlarges considerably towards each extremity. The length of the body is 44 inches.

The median dorsal vertebræ are typical of the Iguanodon, several having been found connected with the extremities and other parts of the skeleton. There is a fine example (Mantellian collection, 2160) on the lower shelf to the left of the group of caudal vertebræ (see Diagram, p. 227); but I have several larger and more perfect than any in the British Museum.

The centrum has the sides smooth, concave in their anteroposterior diameter, and slightly convex in the opposite or vertical direction; the articular faces are nearly flat, or slightly concave; in some examples they are flat in front, and depressed behind; of an oval form vertically, and flattened laterally; the sides of the centrum converge towards each other below, so as to impart a wedge-like shape to the inferior part in a vertical section. The suture uniting the body to the neurapophysis is almost obliterated in the adult state. The neural arch rises into a broad expansion, or platform, which is supported on each side by a strong buttress, or pillar, that springs from the hinder and outer angle of the base of the neurapophysis. The spinous process rises from the entire median width of the neural platform, contracts as it ascends, and inclines gently backwards.

The articulating depression for the head of the rib is of an elliptical form, and is situated on the side of the neural arch; in the anterior dorsals it is placed on the centrum.

The anterior oblique processes are oval, and face each other; their upper margins are four inches apart: but their inferior ones are separated only by a slight notch in front of the spinous process; they extend but little from the neural platform. The hinder oblique processes are sent off from the under and back part, and overhang the posterior surface of the centrum; their articulating facets are turned downwards, and outwards. The upper transverse process is very strong, and of a trihedral form; it is directed upwards and outwards, with an inclination backwards from the sides of the neural platform, and is supported by a diagonal buttress, or

ridge, which passes outwards from beneath, and is gradually blended with the process. The spinal canal is nearly circular, and expands slightly in front, where it assumes a transversely oval outline. The following are the dimensions of the vertebra above described :

Height from the base of the centrum to the neural plat-
form.

Height of the spinous process
Width of spinal canal anteriorly

The essential distinctive characters of the dorsal vertebræ of the Iguanodon, as demonstrated by Professor Owen ("Brit. Reports," p. 127), are the strong, broad, and lofty bony platform into which the neural arch expands, with its supporting buttresses; and the presence of a lower transverse process (parapophysis) for the reception of the head of the rib, either on the side of the centrum, as in the anterior dorsal vertebræ, or from the side of the neural arch, as in the middle dorsal; characters which distinguish these vertebræ from those of ophidians, lacertians, and enalosaurians ; while the absence of the posterior convex facet on the centrum, separates them from those of the existing species of crocodilians and lizards.

The usual condition in which dorsal vertebræ are found, is the centrum or body deprived of its neural arch, as in Lign. 35, fig. 8 (ante, p. 164); specimens with the upper transverse processes (diapophysis of Professor Owen), and the neural arch (as in fig. 6, which is either a posterior dorsal or lumbar), are comparatively rare; a few vertebræ only have been obtained with the spinous process entire. In the Maidstone specimen, (ante p. 146, Plan p. 138, Case No. 23) there is a series of dorsal vertebræ (some are probably lumbar), but these are so much distorted by compression, that not one presents the normal form, either of the body or the apophyses.

The great strength and expansion of the transverse processes of the posterior dorsals indicate the large development of the abdominal region in this stupendous reptilian vegetable feeder.

RIBS.-Wall-case C, lowermost compartment.-There are