4 FOSSIL REPTILIA OF THE 



The following are the characters of the cervical vertebrae in Mr. Bowerbank's 

 young Iguanodon : 



The centrum partakes of the characteristic of that part in the dorsal region, in its 

 lateral compression and the convergence of its sides to a very narrow inferior surface : 

 but this wedge-shaped characteristic is exaggerated in the present vertebras ; the sides 

 are naturally more compressed between the fore and hind articular ends ; they are 

 concave, not only lengthwise but vertically, and they meet below at a ridge from which 

 a process — the hypapophysis — appears to have descended ; for, though the ridge 

 itself, hy, figs. 2 and 4, extends below the level of the articular ends of the centrum, it 

 shows a fractured edge ; and the hypapophysis is the characteristic of the cervical 

 region in most saurian reptiles. As the neural canal retains its original capacity — the 

 arch showing no marks of pressure, — the compression of the middle part of the sides of 

 the centrum cannot be regarded as the effect of crushing ; it is the s'c* t on both 

 sides, and the expanded articular ends seem to exhibit their natural and tj mmetrical 

 form,* as in fig. 4, Tab. I. This form differs from that in the dorsal region,! 

 by being narrower in proportion to its depth, and repeats in this proportion 

 the character of the same part in the caudal region;! but the contour of the cervical 

 centrum is different from that of the caudal one : the anterior surface resembles an 

 ancient shield, the sides slightly diverging as they descend to the parapophyses, and 

 then more rapidly converging to the inferior ridge ; the contour of the hinder surface, 

 fig. 4, is an oval, a little flattened above at the larger end. The deep pit at the side 

 of the centrum characteristic of the cervical and anterior dorsal vertebrae of the 

 Streptospondyl is not present in the corresponding vertebrae of the Iguanodon. In 

 these vertebrae the anterior articular surface is nearly flat vertically, very slightly 

 concave at the middle, and as feebly convex above and below. Transversely the 

 surface is slightly convex, and most so where it is continued, just above the middle 

 of the surface, upon the parapophyses. The hinder surface is gently and pretty 

 uniformly concave. 



Both surfaces are devoid of that smooth or polished character which is observable 

 in the Reptiles that have those surfaces coated by articular cartilage, and have their 

 vertebral centrums articulated by synovial capsules; concentric striae are plainly 

 manifest near the border of the articular surface, whence I conclude that the vertebral 

 bodies of the Iguanodon were coarticulaied by means of an intervertebral ligamentous 

 substance, as in the class Mammalia. That such substance intervened between these 



* The assertion in the paper above cited, 'Phil. Trans.,' 1849, p. 303, that the three vertebrae here 

 described "have been crushed and compressed almost flat laterally" has reference to an idea that they were 

 homologous with the Streptospondylian vertebra described in my 'Report,' p. 92, the different form and 

 proportions of which are explained by the authors of that paper on the assumption that that vertebra " has 

 been compressed in an opposite direction," ib. p. 303. 



f 'Mon. Cretaceous Reptiles,' tab. xxxvi. % lb., tab. xxvii. 



