280 BRITISH FOSSIL REPTILES. 



origin in all the three detached vertebrse : there is a deep angular depression behind 

 its base, between the two converging ridges from the posterior zygapophyses, probably 

 for the implantation of an elastic ligament. 



The proximal end of a slender pleurapophysis, pi. fig. 2, adheres by the matrix to the 

 eft side of the second and third of the tliree vertebrae above described ; the neck of 

 the rib is moderately long and rounded, truncate, and not expanded at its articular 

 end ; the tubercle is produced, and beyond that the rib becomes compressed : unfor- 

 tunately only a small part of the body of the rib is preserved. 



Of the succeeding vertebrae, imbedded in the matrix, the flat or slightly concave 

 character is resumed in the anterior surface of the centrum of the third, counting 

 backwards. 



The modification of the articular terminal surfaces, slight as it is in the cervical 

 vertebrae above described, may be readily understood to relate to the corresponding 

 increase in the extent and facility of motion of that part of the spine. But such 

 modification gives no support to the idea that the vertebra. No. ^'^ in the British 

 Museum, provisionally referred to the Sfreptospondi/hs major in my ' Report on 

 British Fossil Reptiles,' p. 92, but with the intimation of its being possibly a cervical 

 vertebra of the Cetiosaurus brevis (ib., p. 96), — and referred by Dr. Mantell to the 

 Iguanodon Mantelli in the 'Geology of the South East of England,' 8vo, 1833, p. 300, 

 really appertained to the cervical region of the Iguanodon. 



We have not, as yet, any evidence of so marked and sudden a change in the 

 forms and pi'oportions of a cervical vertebra, between the dentata and the fourth or 

 fifth, occurring in any reptile or mammal, as would be the case were the vertebrae, 

 described in p. 92 of my 'Report on British Fossil Reptiles,' 1841, to belong to the 

 Iguanodon; and the absence of such evidence prevents me now, as at the period 

 when those vertebrae were first described, from hazarding or acceding to the 

 hypothesis. 



In the vertebrae succeeding those, i, 2, 3, here regarded as cervical in the young 

 Iguanodon, PI. 6, the sides of the centrum continue to be compressed, with a surface flat 

 vertically, and concave longitudinally, and meeting below at a ridge, as far as the twelfth, 

 counting backwards, and including the three detached cervicals : at the fourteenth 

 vertebra the lower part of the centrum is broader, and is convex transversely. The 

 parapophysis has ascended upon the neurapophysis in the fifth vertebrae, counting 

 backwards ; and in the sixth the contour of the articular terminal surface is oval, with 

 the small end downwards : it is shown to be elliptical in the sixteenth vertebra. 



The neurapophysial sutures are retained throughout the series of the seventeen 

 successive vertebrae. In the seventh, sufficient of the neural arch is preserved to show 

 the interzygapophysial ridge, forming the base of the expanded bony platform, ?i ,- a 

 part of the neural spine, n 5, of this vertebra is preserved, to an extent equaling the 

 vertical diameter of the rest of the vertebrae : it is compressed, but of considerable 



