FEOM THE KIMMEEIDGE CLAY. 443 



the horizontal diameter of the ends did not exceed the vertical as 

 in the neck. The borders of the articular ends are prominent and 

 slightly everted. 



The anterior articular surface of all the praesacral vertebrae behind 

 where the neck and trunk join (in vfhich region it is plane) is 

 slightly hollow ; and this is also its shape in the tail. The posterior 

 articular surface of all the vertebrae behind the neck is decidedly 

 concave. This character — the greater concavity of the posterior 

 articular surface — is of use in determining the direction of a disso- 

 ciated centrum when other indications are lost. 



The sides of the centrum, in what I may call the middle dorsal 

 region, are gently convex in the vertical direction, and concave 

 longitudinally. At its middle the centrum is slightly constricted. 

 The constriction is much less than that represented in the figure of 

 a thoracic vertebra of Iguanodon Mantelli given by Prof. Owen in 

 the Eoss. Eept. of the Wealden formation, Suppl. II. t. 7. fig. 6. 



In Wo. 11 the facet for the rib-head is 9-5 millims. distant from 

 the praezygapophysis ; in No. 13 it is 18*5 millims. from it ; in No. 18 

 the interval is nearly the same. It appears from this that the out- 

 ward movement of the capitular facet, from the root of the (upper) 

 transverse process — diapophysis — to the free end of this, takes 

 place through a larger series of vertebrae in this Iguanodon than in 

 extant crocodiles, and that the middle thoracic region was longer 

 in the Dinosaur. In a skeleton of Crocodilus niloticus, presented in 

 1875 to the Hunterian Museum by the Hon. E. E. C. Berkeley, at 

 the 19th vertebra the capitular costal facet merges into the tuber- 

 cular facet at the free end of the transverse process ; and the rib 

 articulating here retains scarcely any trace of division. In this 

 skeleton the passage of the capitular facet from the centrum to 

 the free end of the diapophysis is completed through a chain of 8 

 vertebrae, the 12th to 19th inclusive. In this Iguanodon's vertebral 

 column the capitular facet, withdrawn from the centrum in No. 8, 

 is still near the root of the diapophysis in No. 18. The large pro- 

 portion of Iguanodont vertebrae in which the rib-head facet is close 

 to the praezygapophysis, which I have obtained in the Isle-of- 

 Wight Wealden beds, had long attracted my notice. 



Behind No, 16 the bulk of the centrum much increases. Many 

 of the centra in the front and middle of the trunk are much crushed ; 

 but, allowance being made for this mutilation, the excess of the 

 horizontal over the vertical diameter, so noticeable in the articular 

 ends of the centra in the neck, is clearly not repeated here. 



In No. 17, where the centrum has escaped distortion, the anterior 

 articular surface has a nearly circular outline ; its horizontal and 

 vertical diameters are each 51 millims. The vertical diameter of 

 the posterior end is also 51 millims., the horizontal being somewhat 

 greater, 57*5 millims. The borders of both ends are prominent, 

 and slightly everted (as in the root of neck) ; and the rugosity of 

 the adjoining part of the lateral non-articular surface is strongly 

 marked. The sides of the centrum here, as in the anterior thoracic 

 region, are gently convex vertically. The inferior median keel is 



