296 
DR. MANTELL ON THE OSTEOLOGY OF 
inches, lines. 
Height of anterior surface of body 3 6 
Width of anterior surface of body 3 7 
Length of the body (inferiorly) 2 1 
Width of spinal canal in centre 5^ 
lu the Crocodile the chevron bone commences at the second caudal and termi- 
nates at the twentieth, but the rib eeases at the fifteenth, the number of vertebrae 
composing the tail being forty-two. 
The four huge caudal vertebrae already mentioned as assigned to the Cetiosaiirus 
brevis*, exhibit very peculiar characters, fully detailed by Professor Owen, and are 
especially distinguished by the absence of projecting posterior articular processes ; 
‘ the posterior articular surfaces being impressed upon the sides of the posterior part 
of the base of the spine,’ while the anterior oblique processes ‘ reach beyond the middle 
of the vertebra next in front, and pinch, as it were, the back part of the base of the 
spine so as to impress upon it the surfaces representing the posterior articular pro- 
cesses.’ If then these anterior caudal vertebrae are characterized by the absence of 
the posterior oblique processes, and as in the succeeding elements of the series the 
invariable tendency is to the disappearance of articular processes whether in front or 
beliind, the terminal angular vertebrae (Plate XXX. figs. 12, 13) in which the posterior 
oblique processes are still well-developed, projecting from the back part of the base 
of the spine, cannot belong to the same species as those just described, without 
violating those analogies which have hitherto held good ; for we cannot well admit the 
reappearance of posterior oblique processes, after they have once subsided, in a more 
posterior part of the same caudal series. Other discrepancies equally marked forbid 
their association. 
There remain then to represent the Cetiosaurus brevis, in the specimens under 
consideration, only the above four caudal vertebrae, which are truly so whale-like in 
their form, as to be pre-eminently worthy of that generic appellation. Probably they 
are portions of one or other of the species of that genus from the Oolites, indicated 
by Professor Owen, chiefly from the more posterior caudal vertebrae. 
The close resemblance which these unique caudal vertobrae'f present to two re- 
markable ones figured by Cuvier:|: from the oolite of Honfleur, was long ago recog- 
nized by Dr. Mantell. They are thus described : ‘ a corps cylindrique, presque 
aussi long que large, marque de chaque cote d’une petite fossette, a faces planes, 
circulaires, a canal medullaire fort etroit, a partie annulaire non articulee ; I’apophyse 
epineuse haute, et droite ; les transverses au niveau du canal medullaire, grosses 
cylindriques, dilatees verticalement au bout ; et, ce qui est tres remarquable, les 
* Ante , p. 294. 
t An outline of one of these vertebrae is given in Dr. Mantell’s Memoir, Philosophical Transactions, 1841, 
Plate IX. 6g. 13. 
\ Tome V. pi. 22, figs. 1 and 2. Oss. Foss. ed. 1824. 
