290 
DR. MANTELL ON THE OSTEOLOGY OF 
all point to a more posterior position in the dorsal series; and we may suppose 
either that the anterior convexity of the body subsided much more rapidly than the 
head of the ribs changed its point of attachment, or that several vertebrae presenting 
a similar configuration of the neural arch, but with a progressively diminishing 
convexity, occurred at the anterior part of the dorsal region, which would indicate a 
less rapid transition between the different forms of the vertebrae, and consequently 
a greater number of them than in the Crocodiles, which might indeed have been 
expected in a herbivore with a bulky trunk, as shown by the huge ribs in the Man- 
tellian collection. 
The dimensions of this very perfect and interesting fossil are as follow : — 
inches, lines. 
Extreme length of the body 4 3^ 
Extreme width of the body 3 3 
Extreme height of body (measured on anterior surface) . ... 4 10 
Antero-posterior diameter of neural lamina where narrowest . . 2 9 
From mesial line anteriorly to extremity of transverse process . . 8 
Antero-posterior diameter of transverse process at root .... 2 9 
Between extreme points of anterior oblique processes .... 3 4 
Width of spinal canal (posteriorly) 1 2 
The body is much contracted in the centre, so that the sides are deeply concave 
lengthwise, but convex vertically ; they converge towards each other below, thus a 
vertical section presents a wedge-shaped outline with convex sides. The neuropo- 
mal sutures are obliterated, but the share contributed to the body by the expanded 
bases of the neural laminae is equal to that indicated by the detached neural arch in 
Mr. Saull’s collection. The neural lamina (/) is coextensive Muth the supporting 
centrum, but it contracts slightly as it ascends, and so that the posterior notch is 
still the deepest. The spinal platform is also excavated in front for the reception of 
the posterior oblique processes ; the base of the spine (c) increases in thickness as it 
passes backwards and rises on the thick hinder portion of the platform. The anterior 
articular facets (/*) are oval, look towards each other, and their inferior margins meet 
nearly at right angles, separated only by a slight notch, and further back by the thin 
anterior edge of the spine. The strong trihedral transverse processes pass outwards and 
upwards with an inclination backwards from the sides of the spinal platform, and are 
as it were twisted on their axes, so that the upper surface slopes forwards and down- 
wards internally, but backwards and downwards externally ; both edges are thin ; be- 
low it is supported by a more strongly developed diagonal buttress-like ridge, passing 
outwards beneath, and gradually subsiding into the transverse process, giving it an 
increased thickness. This ridge separates two fossae on the free aspect of the neuro- 
pome ; the anterior is more or less obliterated by a rough excrescence, which articu- 
lates with the head of the rib (/) ; the posterior is remarkably deep, partly roofed 
over by the base of the plagiapophysis, and separated from that of the opposite side 
