444 J. W. HULKE ON IGUANODON PRESTWICHII 



less prominent here than in the last-mentioned region. The con- 

 striction of the middle of the centrum is also in these Cumnor 

 fossils less than in those from the Wealden formation, described in 

 the work to which reference was very lately made. The transverse 

 horizontal diameter of No. 17 at its middle is 41 millims, at the 

 anterior end 51 millims, and at the posterior end 57 millims. In 

 this part of the column the prsezj^gapophysis has a more horizontal 

 direction than in the front of the trunk. 



In the loins the centrum increases greatly in bulk, and this more 

 by augmentation of its width and depth than by addition to its 

 length. In No. 21, which I place here,- the horizontal diameter of 

 the anterior articular surface is 64 millims., and the vertical dia- 

 meter 56 millims.; the same diameters of the posterior articular 

 surface are 74 and 52 millims., the horizontal diameter in both 

 instances preponderating. The average length of the centrum in 

 this region is 54 millims. These proportions give to the lumbar 

 centra an appearance of stoutness and shortness. The anterior 

 articular surface is very flat, whilst the posterior surface is dis- 

 tinctly concave, the concavity being greater in tbe vertical than in 

 the horizontal direction. The sides of the centrum are, in the 

 vertical direction, more cylindroid than in the dorsal region. The 

 inferior keel is more marked than in the posterior dorsal vertebrso, 

 owing to a slight flattening of the surface on each side of it, which 

 increases its prominence. The anterior articular processes look 

 inwards and upwards. The posterior articular processes greatly 

 overhang the plane of the posterior surface of the centrum. They 

 are separated from one another by a deep groove. The neuro-central 

 suture is almost the same length as the upper surface of the cen- 

 trum; but the neurapophyses soon contract, principally by the 

 forward slant of their posterior border. In No. 20 the lengths of 

 the neuro-central suture and centrum are 50 millims., whilst at 

 the height of 15 millims. the neurapoph5^sis has an antero-posterior 

 extent of only 32 millims. (PI. XIX. figs. 6-8.) 



The spinous processes of all the prsesacral vertebrae have been 

 broken off. So far as may be gleaned from the stumps remaining 

 on some of the arches and from detached dissociated fragments, 

 they had in the trunk a great antero-posterior extent ; near their 

 root their front margin is a thin edge ; their posterior border is 

 deeply grooved ; they had a backward slant. In none of the trunk- 

 vertebrae is there any indication of a capitular costal facet on the 

 pier of the arch, as represented in the figure of the dorsal vertebra 

 of Iguanodon Mantelli in the Eossil Rept. of the Cret. and Weald. 

 Formations, p. 109, pi. 35 ; and the evidence afforded by these remains 

 (it is not claimed to be complete) seems to show that the rib-head 

 facet, when it left the neuro-central suture, passed directly from this 

 to the (upper) transverse process, as in extant crocodiles. In the 

 skeleton of Croc, niloticus the transfer occurs at the 12th vertebra, 

 in which the capitular facet is on the diapophysis, whilst in the 11th 

 vertebra it is on the neuro-central suture. 



Sacrum (PI. XX. figs. 1, 2). — The true sacral vertebrae (as defined 



