[582] To obtain a correct knowledge of the osteological structure of fossil Reptiles, the student should consult Baron Cuvier’s Ossemens Fossiles, tom. v. To the English reader, the translated abridgement of Cuvier’s "Fossil Remains of the Animal Kingdom," by E. Pidgeon, 1 vol. 8vo. with plates, 1830, will be found a very instructive volume. See also Penny Cyclopædia, Art. Saurians.

Vertebræ of Reptiles.—The bones of the vertebral column of this class of animals present such numerous and important modifications in the different orders and families, that reference to the works already cited must be made for satisfactory information on this topic. From the great number of vertebræ in many reptiles, amounting in the individuals of some species to nearly two hundred, these bones are the most abundant fossil relics of these animals to be found in our collections. The vertebræ are commonly detached, and deprived of their processes; the solid centrum, or body, alone remaining in most examples (as in [Lign. 206], fig. 8). Connected series, more or less complete, are occasionally discovered; and the entire column, in connexion with other parts of the skeleton, is preserved in many specimens in the British and other museums.[583] Although, for the reasons previously stated, minute osteological details cannot be attempted in this work, some acquaintance with the elementary characters of the bones composing the spinal column, and of the nomenclature employed to distinguish them, is necessary to guide the student, and even the amateur collector, in their researches. I have, therefore, selected a few specimens from Tilgate Forest in illustration of the elements of Saurian vertebræ, and of the terms by which the different processes are distinguished; the general reader will thus be enabled to comprehend the descriptions of these structures in other works on Palæontology.

[583] See Petrifactions, pp. 136-352, and pp. 362-387.

Lign. 206. Fossil Vertebræ or 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.
3a.——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 Streptospondylus: 1/16 nat.
6.—Lumbar vertebra of Iguanodon, with the neural spine broken off.
7.—Vertebra of Streptospondylus: 1/16 nat.
c. The pair of posterior oblique processes (zygapophyses).
8.—The bodies of two dorsal vertebræ of Iguanodon: viewed laterally.
The same letters refer to the same 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, formed of the two neurapophyses, which contains the spinal cord.
c, c.The articular or oblique processes (zygapophyses), which join to the next vertebra in front.
d.The spinous process or neural spine of the annular part.
e, e.The transverse process of the annular part.
f.The chevron-bone, formed of the two hæmapophyses and the hæmal spine
g.The double articulating head of the chevron: the passage left by these processes (hæmal arch), seen in the front view, figs. 2 and 3, is for the passage of the large blood-vessels which supply the tail.
h.The spine of the chevron-bone; the inferior spinous process, or hæmal spine.
i.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.

The bones composing the spine, are not only designed to form a flexible column of support to the trunk, but also to afford protection to the grand nervous chords constituting the spinal marrow, and which extend from the brain to the tail, and give off numerous lateral branches in their course, conferring sensation and motive power to every part of the frame. To effect this purpose, there is attached to the upper or dorsal part of each vertebra a bony ring, called the neural-arch, which is composed of two processes ([Lign. 206], b.), arising from each side of the body or centrum ([Lign. 206], a.), and which unite above into a solid piece, termed the spinal process, ox neural spine ([Lign. 206], d.). On each side of the annular paid there is a process, called the transverse ([Lign. 206], e, e.), for the attachment of muscles; and in the middle and the posterior dorsal regions of some reptiles, as, for example, in the existing Crocodiles, these processes articulate with the ribs. The vertebræ of the tail have, in addition to the above, an inferior spinous process, termed the chevron-bone ([Lign. 206], fig. 2, and fig. 3, f.), which gives support to the inferior layers of the caudal muscles; and, bifurcating at its attachment to the body of the vertebra, leaves a channel for the passage of the large blood-vessels, by which the circulation of the tail is effected.