ON BRITISH FOSSIL, REPTILES. 127 



surface of the centrum in order to rest upon the oblique processes of the ver- 

 tebra next behind. In the anterior dorsal vertebraa the body supports a large 

 and well-marked articular surface on each side, for the head of the rib ; and 

 a long and strong transverse process is developed from each neurapophysis 

 against the end of which the tubercle of the rib abuts, as in the Crocodile. 

 In the hinder costal vertebrje the long transverse process is gradually nar- 

 rowed to its extremity, which is abruptly truncated, and has a right-angled 

 notch at the anterior part ; the curtailed neck of the rib, no longer expanded 

 into a head or joined to the body of the vertebra, is fitted into this notch, 

 and the broad and flat surface; at right angles to the neck, is adapted to the 

 extremity of the transverse process. 



We seek in vain, in the existing Iguana, for such modes of articulation of 

 the ribs as have here been described, while they are common to Crocodiles with 

 the Dinosaurs. The fact of the complete inclosure of the spinal canal by 

 the meeting and confluence of the bases of the neurapophyses beneath it, 

 was first brought to my attention by the appearances in the body of a dorsal 

 vertebra of the great Horsham Iguanodon, in the collection of Mr. Holmes. 

 This centrum, which measures 4|- inches in length and 5 inches across its 

 articular extremity, presented only a slight trace of the impression of the 

 spinal canal at the anterior part of its upper surface, the rest being occujjied 

 by a slightly concave, continuous, rough articular surface. The deficiency 

 of this vertebra was supplied by a fine specimen in Mr. SauU's collection of 

 the separate neural arch of a dorsalVertebra of a corresponding size, which 

 seemed to have been detached from a natural articulation. I saw with much 

 interest that the bases of the neurapophyses met and joined each other below 

 the spinal canal along the posterior half of their longitudinal extent, present- 

 ing at their under part a continuous slightly convex surface, which must have 

 left a corresponding concave rough articular surface upon the upper part of 

 the centrum, like that exhibited by the Horsham vertebral body. The base 

 of each neui'apophysis, which is longer than it is wide, describes a slight 

 curve, convex in the antero-posterior direction, downwards or towards the 

 centrum. The spinal canal is nearly cylindrical, very slightly expanded at the 

 two extremities ; its diameter 1 inch 5 fines. The chief buttress of the spinal 

 platform rises from the posterior and outer part of the base of the neurapo- 

 physis, and ascends almost vertically, slightly inclining forwards ; it is com- 

 pressed, with its plane transverse to the axis of the vertebra ; it expands as 

 it blends with the under part of the broad platform, half-way between the 

 anterior and posterior boundaries of that remarkable part of the neurapophy- 

 sis. A second buttress rises from the anterior part of the base of the neura- 

 pophysis, and ascends vertically to the upper and outer end of the anterior 

 oblique processes. The base of the transverse process is situated above the 

 converging point of the two buttresses. In the interspace of the two but- 

 tresses of the anterior dorsal vertebrae there is a large oval articular surface, 

 convex at the anterior and concave at the posterior part, which has aff'orded a 

 lodgement to the head of an enormous rib. The oblique or articular processes, 

 directed as described in the general observations on the vertebra of the Igua- 

 nodon, converge and meet at nearly a right angle. There is a wide depression 

 at the posterior broad part of the base of the spine, and a wide and deep fossa 

 between the posterior buttress and the posterior oblique process. The base of 

 tlie spine, as it extends forwards along the middle of the broad platform, de- 

 scends with a graceful curve to the interspace of the anterior oblique pro- 

 cesses. The platform recedes on each side from the base of the broad spine 

 with a regular concavity to its plane ; its surface is coarsely striated trans- 

 versely. 



