THE IGUANODON AND H YL.EOSAURUS. 
289 
corresponding to a thick median crest. The body is constricted in the centre so that 
the sides are concave parallel to its axis, but convex vertically, owing to the great 
prominence of a broad longitudinal ridge, equivalent to that bearing the perapophy- 
sial surface in the cervical ; above and below which there is also a deep concavity. 
The spinal canal {j) has a transversely oval outline, and enlarges considerably 
towards each extremity. The neural lamina {h) contracts suddenly, though slightly, 
and chiefly from behind forwards above its expanded base, so that the posterior notch 
is much the deeper; its external surface is impressed by a deep and rough irregular 
fossa (/) for the insertion of the head of the rib, bounded behind by a sharp pro- 
minent ridge ascending obliquely forwards from near the posterior and inferior angle 
of the base of the neuropome, and passing outwards on the under surface of the 
plagiapophysis {d). In front, this perapophysial surface (/) is deflned by a thin 
margin arching backwards to meet the above-mentioned buttress-like ridge at the 
root of the transverse process, which is detached, but springs with an inclination 
upwards from the side of the spinal platform. The spinous, anterior, and posterior 
oblique processes, are unfortunately wanting; but the anterior oblique processes 
do not approximate to each other so closely as in the more posterior vertebrae, in 
which they are merely separated by the trenchant anterior edge of the spine ; from 
this we may infer that the long peduncles of the met-arthropophyses in the cervical 
vertebrae have coalesced at their bases to support the more strongly developed spine, 
but that their apices bearing the articular facets are still separated by a wide notch, 
more or less filled up by the base of the neuracantha (c), which decreases in width as 
it extends forwards to the anterior edge of the neural arch ; its line of attachment 
sweeping downwards at the same time from the excavation of the spinal platform in 
front for the reception of the oblique processes of the preceding vertebra. The ex- 
panded bases of the neural laminae are defined by the direction of the superficial 
striae, and doubtless coalesce more or less completely in the mesial line, commencing 
in front, to exclude the centrum from any share in the formation of the vertebral 
canal. The dimensions of this most instructive specimen are subjoined. 
inches, lines. 
Length of the body between the centres of the articular surfaces . 4 3 
Greatest width of body 4 3 
Greatest height of body 6 6 
Antero-posterior diameter of neural lamina where narrowest . . 2 9 
Width of spinal canal 1 9 
Height of spinal canal 1 4 
The next vertebra to be described, Plate XXIX. fig. 8, differs from that just men- 
tioned, in the flatness of the anterior articular surface (a'), and in the almost com- 
plete obliteration of the posterior concavity («"), in the less central constriction of 
the body, and in the absence of its inferior median ridge. Notwithstanding the situa- 
tion of the perapophysial surface on the side of the neuropome, the above characters 
