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working its vast tail, as an oar, from side to side, and not upwards 
and downwards, as in the cetacea. 
In the monitors the tail is rounder, and the transverse apophyses 
reach much further. In the crocodiles, the basilisks, the lizards, the 
stellions, and in the lizard tribe in general, except the monitors, and 
even in the cetacea, and in all the quadrupeds with a large tail, the 
angular bone is articulated on the lower part of the joining of the 
vertebrae, and is therefore common to two vertebras. 
The monitors alone have beneath the body of each vertebra two 
surfaces for its reception, as in this animal ; only the body of their 
vertebrae being more elongated, these surfaces are on them placed 
more posteriorly. In the fossil animal, these surfaces are near the 
middle. But M. Cuvier observes, that he does not know any animal, 
in which the angular bone is united in one body with the vertebra, as 
it is in this, through the posterior part of the tail, by which its solidity 
is of necessity much augmented. 
Another character, distinguishing the fossil animal from the monitors, 
and from others of the lizard tribe, is the sudden ceasing of the arti- 
cular apophyses of the vertebrae, which takes place in the middle of 
the back, whilst, in the greater part of animals, they extend very 
nearly to the end of the tail. 
The first twenty vertebrae of the tail appear to have had no angular 
bones attached to them ; whilst, in the crocodile and monitors, only 
one or two vertebrae of this description exist. Hence the tail of this 
animal must have been in all probability, cylindrical at its base, and 
have enlarged in a vertical direction, and become flattened, only at 
some distance from the body, assuming the form of an oar much more 
than is the case in the crocodile. 
Besides other differences between these vertebrae and those of the cro- 
codiles, it is observable that those of the neck, in the fossil, do not possess 
the two tubercles which, in the crocodile, bear the little false rib on each 
side; which is another proof that this animal was not a crocodile, and 
that it possessed more liberty of moving its head from side to side. 
