292 
DR. MANTELL ON THE OSTEOLOGY OF 
length of the platform, which presents a median notch in front, separating the pro- 
jecting anterior oblique processes, whose oval facets are almost horizontal, being in- 
clined to each other only at a very obtuse angle. The strong transverse processes 
project outwards, with a slight inclination upwards from its lateral edges, their upper 
surfaces sweeping gently upwards to the lateral aspects of the spine. The antero- 
inferior edge of the plagiapophysis is thick, and about 2 inches external to its base 
bears the rough facet for the head of the rib (/), beyond which this process contracts 
suddenly in antero-posterior extent to lodge the neck of the rib ; its extremity is 
however lost. The thickness of the transverse process diminishes to its posterior 
edge, and below the diagonal buttress already mentioned in the preceding descrip- 
tions, supports it, and is prolonged outwards on the slender portion of the process. 
The posterior deep fossa behind the buttress exists also, but the anterior is obliterated, 
the outer surface of the neural lamina being only slightly convex from before back- 
wards, and subconcave vertically. 
The spine ascends obliquely backwards and is of nearly equal width throughout; 
in its basal half it diminishes rapidly in thickness towards its anterior thin margin, 
which is prolonged forwards to the edge of the platform ; in its upper moiety it con- 
tracts slightly behind ; the posterior border presents a deep groove, obliterated in the 
upper third by a rough ridge rising from its floor ; the apex is broadly truncated and 
the hinder angle removed ; the anterior border is carinate below, but above exhibits 
a well-marked excavation, becoming wider and deeper above. The greatest diameter 
of the transverse process at its root is 2 inches 9 lines ; between the articular surfaces 
of opposite sides, for the head of the rib, it measures 8 inches 5 lines. The length of 
the spine anteriorly is 12 inches 5 lines, its greatest antero-posterior diameter is 
3 inches 4 lines, and its greatest thickness 2 inches 3 lines. The greatest width of 
the centrum is equal to 4 inches 5 lines. The extreme height of this vertebra is 
1 foot 8 inches. 
Undoubted lumbars of the Iguanodon have not hitherto, so far as 1 am aware, been 
recognized, although some of the vertebrae preserved in the Maidstone specimen 
may belong to that region of the spine. The presence of an articular facet on the 
transverse process for the attachment of the rib is the distinctive character between 
the posterior dorsal and lumbar vertebra ; unfortunately these processes being readily 
detached are usually absent. However, we may expect certain modifications in the 
neural arch of, and also a more robust, perhaps, shorter body in, the vertebrae of the 
lumbar region. As in Crocodiles, the transverse processes would continue to spring 
at the level of the spinal platform, but the absence of the rib would cause a further 
simplification in the sculpturing of the neural lamina, and thus the supporting dia- 
gonal buttress of the transverse process would wholly disappear. The neural laminae 
themselves would have a less antero-posterior extent than in the more anterior ele- 
ment of the column, and hence the notches and uncovered tracts of the body would be 
more marked than in the dorsal vertebrae, where great strength and size are required 
in the arch to support the huge ribs of this herbivorous, and it may be, ruminating 
