data. It is only by a strict regard to truth, and the substitution of facts for hypotheses, that the science of Paleontology can be extended, and its principles securely established.

From the great number of vertebræ in many reptiles, amounting in the individuals of some species to nearly two hundred, these bones are, perhaps, the most abundant of all the fossil relics of this class of animals. In many deposits, the vertebræ are almost always deprived of their processes, the body or centrum alone remaining, (as in Lign. 35, fig. 8). In other strata, entire series, with the processes more or less perfect, and in connexion with other parts of the skeleton, are found imbedded; as in the beautiful specimens of Ichthyosauri and Plesiosauri in the lias limestones and shales.

As vertebræ, or their detached processes, are frequently the only vestiges of peculiar types of extinct saurians, a few explanatory remarks are necessary to enable the reader to appreciate the interest and importance of some of the specimens in this collection, which are apparently but of very little value.

The bones composing the spine are designed to form a flexible column of support to the trunk, and afford protection to the great nervous chords constituting the spinal marrow, and which extend from the brain to the tail, giving off numerous lateral branches in their course, and conferring sensation and motive power to every part of the body. To effect this purpose, the upper part of each vertebra consists of a ring, called the annular part or neural-arch, which is composed of two processes (Lign. 35, b.), arising from each side of the body, or centrum (Lign. 35, a.), with which they are connected by suture, and these unite above into a solid piece, termed the spinal process (Lign. 35, d). On each side of the annular part there is a transverse process, (Lign. 35, e, e.), for the attachment of muscles; and, in some reptiles, as the Crocodiles, the ribs are articulated to these processes.

The vertebræ of the tail have, in addition to the above apophyses, an inferior spinous process, termed the chevronbone (Lign. 35, fig. 2 and 3, f), which supports the inferior layers of caudal muscles, and is articulated to the inferior margin of the body of the vertebra, either by two distinct heads, or by the confluence of the two lamina into a single tubercle, (as in fig. 2); in either case an interspace is left

LIGN. 35. FOSSIL VERTEBRE OF REPTILES; TILGATE FOREST. (The figures are reduced in the proportions specified by the fractions.)

Fig. 1.-Caudal vertebra of an unknown reptile.

2.-Chevron bone of IGUANODON: seen in front.

3. Caudal vertebra of IGUANODON, viewed laterally in an oblique direction. 34.-Front view of the same.

4. Caudal vertebra of IGUANODON, without either transverse process or
chevron-bone. The letter o marks the deep hollow left by the removal
of the transverse process, at the suture of the annular part.
5.-Vertebra of STREPTOS PONDYLUS? nat. size.

6.-Lumbar vertebra of IGUANODON, with the spinous process broken off.
7. Cervical vertebra of STREPTOSPONDYLUS?nat. size.

c. The pair of posterior oblique processes.

8. The bodies of two dorsal vertebræ of IGUANODON: viewed laterally.
The same letters refer to the analogous parts in the respective figures; with
the exception of c, in fig. 7.

a. The body, or centrum, of the vertebra: the letter denotes the anterior part.
b. The annular part (neurapophysis), which surrounds the spinal cord.
c, c. The anterior articular or oblique processes.

d. The spinous process of the annular part.

e, e. The transverse processes, or parapophyses.

f. The chevron-bone (hamapophysis), or inferior spine of the vertebra.
g. The single articulating head of the chevron-bone: the interspace seen
in the front view, fig. 2, is for the passage of the large blood-vessels
which supply the tail.

h. The spine of the chevron-bone.

i. The shaded spot, d, denotes the medullary cavity of the annular part. o, o. Mark the sutures which connect the annular part with the body of the vertebra.

w, w. Indicate the place of attachment of the chevron-bone, which in the Iguanodon is always single.

for the passage of the large blood-vessels which supply the tail.

In most of the existing reptiles, (as for example the Crocodile, Iguana, &c.) the bodies of the vertebræ are concave in front and convex behind,' forming a series of ball and socket joints; but in many extinct genera both the articulating surfaces are flat, or slightly concave ;2 or flat in front and concave behind.3

In quadrupeds the annular part is anchylosed to the vertebral centre; in reptiles it is generally united by suture; but all traces of this mode of connexion are often obliterated in aged individuals. By reference to Lign. 35, and its description, the form, arrangement, and connexion of the different vertebral elements in certain fossil reptiles, may be easily comprehended. The bones in the spinal column of the same animal are considerably modified in the several regions of the neck (cervical), back (dorsal), and tail (caudal). The cervical are generally of the most complicated structure, and the caudal, the most simple.

From this exposition, the reader will perceive that every vertebra consists of the following essential parts, namely, the body, or centrum, and the annular part, or neurapophysis, so termed, because it protects the nervous chord ; while a caudal vertebra has, in addition, the chevron-bone, called also hæmapophysis, from its affording a passage to the large bloodvessels,

The bodies of the vertebræ are in general solid, and consist of the ordinary osseous structure; but in certain fossil reptiles the centre of the bone is filled with calcareous spar, indicating an irregular medullary cavity; but this structure also obtains in the caudal vertebræ of mammalia, for example, in our domestic Ox.*

1 Named by Professor Owen procalian vertebræ; from two Greek words, signifying concave before.

2 Amphicalian, concave at both ends.

3 Platycælian, flat in front, concave behind.

I am not aware that this fact was noticed by any anatomist, till pointed out by me in a Lecture on the Structure of Fossil Saurians, delivered in the LONDON INSTITUTION. As some Palæontologists have ascribed a specific and even generic value to this character, I annex figures of transverse and longitudinal sections of a vertebra of the

The Sacrum, which is the key-stone of the pelvic arch that sustains the weight of the body on the hinder extremities, is formed in existing Saurians of two vertebræ, the bodies of which are coalesced; and the posterior extremity of the distal vertebra instead of having a ball or convexity, as in all the bones composing the anterior part of the spine, is concave. The transverse processes are very strong, thick, and broad.

In the colossal Saurians of the Wealden and Oolite, the Iguanodon, Hylæosaurus, Megalosaurus and Pelorosaurus, (and I believe also in two other genera,) the sacrum is composed of five or six vertebræ anchylosed into a solid bony arch, as in Mammalia and Birds, with peculiar modifications in the arrangement of the apophyses; of which we shall have to treat more particularly in the sequel.

BICONVEX CAUDAL VERTEBRA (Lign. 37).—The first caudal vertebra in the existing species of Crocodilian reptiles is remarkable on account of its double convexity, a peculiarity that appears to have escaped the observation of Baron Cuvier, and other anatomists.

In 1835, the discovery of the remains of a fossil Crocodile in the Wealden strata near Swanage, (in Case A,) led me to institute a careful examination of the vertebral column of a large Gavial, in the collection of my distinguished friend Dr. Grant, of University College; for at that time there was not an articulated skeleton of a crocodile in the Hunterian Museum. I then observed that the body of the first caudal

tail of an Ox, to show the relatively large medullary cavity; a fact, of which those who indulge in the luxury of Ox-tail soup may easily satisfy themselves.

LIGN. 36.-SECTIONS OF CAUDAL VERTEBRÆ OF THE OX.

vertebra in the adult Gavial is convex at both ends; a remarkable modification, required to connect the caudal series with the sacrum, in consequence of the concavity of the posterior articulation of the distal sacral vertebra; this mechanism confers freedom of motion without risk of dislocation. The value of a knowledge of this fact to the paleontologist was quickly shown by the occurrence of a biconvex vertebra among some Crocodilian bones from the Sewalik Hills, transmitted to Dr. Buckland by Major Cautley and Dr. Falconer. This bone had given rise to many vague conjectures before the announcement of my discovery of this peculiarity in the first caudal, which is the only vertebra of the series that presents such a structure,' and the only anterior caudal that has no chevron-bone or hæmapophysis, (see Lign. 37).

I must pass over other osteological characters, and proceed to describe the interesting specimens which have called forth these preliminary remarks. The student in comparative anatomy, whose interest may be awakened by these brief comments on the anatomical structure of the extinct types of

1 On my return to Brighton, after a careful admeasurement of the different parts of Dr. Grant's fine skeleton of a Gavial, in order to determine the generic relation of the Swanage Crocodile, I was surprised to find that the double convexity of the first caudal was not mentioned in the works of Cuvier, or in those of any other author to which I had access; I therefore wrote to my kind friend, Dr. Robert Grant, and requested him to examine the skeleton; the following is an extract from his reply:

"You are quite correct. The first caudal vertebra of the Gavial, the Crocodile, and the Alligator is, like the last cervical of Tortoises and Turtles, convex at both ends of its body. It is not so in the Monitors, nor I believe in the other families of Sauria, nor in the Chelonian reptiles.

"In a very young Gavial before me, these sacro-coccygeal surfaces are as flat as in the vertebræ of quadrupeds, while in the Crocodile and the Alligator at the same early period, the first coccygeal is as conver anteriorly as you have observed it in the adult Gavial. The last sacral is, of course, deeply concave posteriorly to receive the anterior ball of the first caudal vertebra. I am not aware that you have been anticipated by any one in your observations on this part of the osteology of the Gavial."

"London, 15th March, 1836.

"ROBERT E. GRANT."

To place this fact on record as a guide to future investigators, I sent a short description, with a sketch, to the "Lancet," which was published in that Journal, June, 1836.

The annexed figure, (Lign. 37,) represents, on a reduced scale, the