82 HADROSAURUS. 
occupies a broad elliptical space, the outline of which is distinctly evident, extend- 
ing between the prominent borders of the articular faces of the body. 
The ossific structure of the vertebre 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 vertebra 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 vertebre 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, where 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. Im 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 series, and ceased to exist altogether 
in the posterior caudals. 
The specimen of an anterior caudal above described, in which the spinous process 
has been preserved entire, may serve to guide us in attempting to estimate the depth 
and breadth of the tail of Hadrosauwrus. 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 in the posi- 
tion of this vertebra would 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 /guana and Cyclura. 
The vertebra of Hadrosaurus bear a near resemblance to those referred to the 
Iguanodon by Drs. Mantell and Melville.' In both genera the cervical series are 
convexo-concave, which character is retained in a less degree in the anterior dorsal 
vertebree. In Jguanodon, according to the authors just mentioned, the posterior 
dorsal and anterior caudal vertebre are plano-concave, which may likewise be the 
case in the corresponding bones of the Hadrosawrus, 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 Hadrosauwrus are described as 
biconcave. In both genera the posterior caudals are biconcave. 
Prof. Owen says: ‘“ Both articular ends of the vertebree of the Jyuanodon are 
nearly flat, thereby differing more from the concavo-convex vertebrae of the Jyuana 
than those of any of the existing Crocodiles or Lizards do.’? According to this 
1 Addit. Obs. on the Osteol. of the Iguanodon, &e. Phil. Trans. Roy. Soc., Lond., 1849, p. 271. 
® British Fossil Reptiles, Pt. VI, Dinosauria, p. 324. 
