82 



UADROSAURUS. 



occupies a broad elliptical space, the ovitliue of which is distinctly evident, extend- 

 ing between the prominent borders of the articular faces of the body. 



The ossific structure of the vertebrae is coarse, and the articular surfaces of the 

 bodies are rather uneven and roughened. The specimens generally present no 

 conspicuous vascular foramina, and only a few of them exhibit one or two moderate 

 sized orifices of this kind at the lower part of the body. 



From the description of the vertcbrfe it may be perceived that they increase in 

 size to the posterior part of the dorsal series. In comparison with the latter the 

 anterior caudal vertebrae undergo a great increase in breadth and depth, but decrease 

 in length. Subsequently the caudals gradually diminish in depth and breadth, but 

 increase in length to near the end of the tail, Avhere they again slightly decrease 

 in the latter direction. 



In the cervical series of vertebrae the bodies are prominently convex in front, 

 and in a corresponding degree concave behind. These conditions are maintained 

 in the anterior of the dorsal series, but subsequently the convexity is depressed 

 and the concavity becomes more shallow, and even the posterior dorsals have 

 assumed a moderately biconcave character. In the caudal series the vertebral 

 bodies are decidedly biconcave throughout. 



The transverse processes of the anterior caudal vertebrae appear to have been of 

 robust proportions, but rapidly declined in the scries, and ceased to exist altogether 

 in the posterior caudals. 



The specimen of an anterior caudal above described, in which the spinous process 

 has been ]jroscrved entire, may serve to guide us in attempting to estimate the depth 

 and breadtli of the tail of Eadrosaurus. The vertebra I suppose to be the seventh 

 or eighth caudal, and if we assume that it possessed a chevron bone of half the 

 length of the vertebral arch together with its spinous process, the tail m the posi- 

 tion of this vertebra Avould have measured about a foot and a half in depth, and 

 about eight inches in thickness. Such a form of tail, though admirably adapted to 

 swimming, would, however, not be incompatible with terrestrial habits, as we observe 

 in the living Iguana and Cyclura. 



The vertebrae of Hadrosaurus bear a near resemblance to those referred to the 

 Iguanodon by Drs. Mantell and ]\[elville.^ In both genera the cervical series are 

 convexo-concave, which character is retained in a less degree in the anterior dorsal 

 vertebrae. In Iguanodon, according to the authors just mentioned, the posterior 

 dorsal and anterior caudal vertebrae are plano-concave, which may likewise be the 

 case in the corresponding bones of the Iladrosaurvs, but in the specimens under 

 examination, the anterior articular surface of the bodies is slightly depressed, so 

 that the posterior dorsals and anterior caudals of Iladrosaurns are described as 

 biconcave. In both genera the posterior caudals are biconcave. 



Prof. Owen says : " Both articular ends of the vertebra; of the Iguanodon are 

 nearly flat, thereby differing more from the concavo-convex vertebrae of the Iguana 

 than those of any of the existing Crocodiles or Lizards do."' According to this 



' Addit. 01)s. on tlie Oateol. of the Iguanodon, &e. I'liil. Trans. Jloy. Soc, Lond., 1849, p. 271 

 « British Fossil Reptiles, Pt. VI, Dinosauria, p. 324. 



