THE IGUANODON AND HYL^OSAURUS. 
287 
vier’s first Gavial of Honfleur. The Amphicoelian and Procoeiian forms are gene- 
rally continued through the whole length of the vertebral column; the Streptospon- 
dylian modification in the last sacral replaces, and in the first caudal is superadded 
to, the Procoeiian 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 Lacertse, but will lead 
us into error if rigidly applied to the more highly organized extinct Saurians and 
Crocodiles. The relative length of the 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 these cervical vertebrse referred to the Streptospondylus major, when 
compared with the shortness of the dorsal or lumbar vertebrse assigned by him to the 
Cetiosaurus brevis, Professor Owen was unwilling to associate them together as be- 
longing to the spinal column of the same species, which, however, appears to be 
really the case, as I shall afterwards have occasion to demonstrate. 
The body of the cervical vertebra, Plate XXVIII. fig. 4, though somewhat crushed, 
well displays the peculiar characters of this region of the spine. Its dimensions are 
as follow : — 
inches. 
Length of body between the centres of the articular facets . . . 3f 
Extreme length, including convexity 5^ 
Length of body (inferiorly), exclusive of convexity ..... 
Height of body posteriorly 3^ 
Width of posterior concave surface 5 
Extent from the extremity of one transverse process to the other. 9 
Transverse diameter of the spinal canal if 
The centrum (a) is depressed, and yields a subpentangular section with the apex 
below; it is broader than high, but the width is nearly equal to the length. The 
anterior articular facet («') is convex, the posterior (a") deeply concave with thin 
edges ; both have a wide oval contour. The lateral aspect presents a deep concavity 
beneath the root of the neural lamina, bounded inferiorly by a ridge (e) faint and ex- 
panding behind, but developed in its anterior third or half into a flat oblong facet (per- 
apophysis), for articulation with the head of the rib. Below the transverse ridges the 
surfaces of the opposite sides, concave outwards, rapidly converge to a broad median 
Carina widening behind, which does not appear to be developed downwards in front 
into a distinct spine as in Crocodiles. How much of the body is contributed by the 
expanded bases of the neural laminm cannot be readily determined, the sutures being 
obliterated ; from the great width of the vertebral foramen in the neck, it is most 
probable that they do not meet mesially, and exclude the centrum from entering 
into the composition of that foramen, as is the case in the dorsal region of the spine. 
2 p 2 
