214 
LIFE OF DEAN BUCKLAND . 
[CH. VIII. 
of a monitor maintained throughout the whole skeleton, 
with such deviations only as tended to fit the animal for 
its marine existence. 
“ The Mosasaurus had scarcely any character in common 
with the crocodiles, but resembled the iguanas, in having 
an apparatus of teeth fixed on the pterygoid bone 
and placed in the roof of its mouth, as in many serpents 
and fishes, where they act as barbs to prevent the 
escape of their prey. The other parts of the skeleton 
follow the character indicated by the head. The vertebra; 
are all concave in front, and convex behind ; being fitted 
to each other by a ball and socket joint admitting easy 
and universal flexion. From the centre of the back to 
the extremity of the tail, they are destitute of articular 
apophyses, which arc essential to support the back of 
animals that move on land ; in this respect they agree with 
the vertebrae of dolphins, and were calculated to facilitate 
the power of swimming ; the vertebrae of the neck allowed 
to that part also more flexibility than in the crocodiles. 
1 he tail was flattened on each side, but high and deep 
in the vertical direction, like the tail of a crocodile, forming 
a straight oar of immense strength to propel the body 
by horizontal movements analogous to those of sculling. 
Although the number of caudal vertebra; was nearly the 
same as in the monitor, the proportionate length of the 
tail was much diminished by the comparative shortness 
of the body of each vertebra ; the effect of this variation 
being to give strength to a shorter tail as an organ for 
swimming ; and a rapidity of movement which would 
have been unattainable by the long and slender tail of the 
monitor, which assists that animal in climbing. There is 
a further provision to give strength to the tail, by the 
chevron bones being soldered firmly to the body of each 
vertebra, as in fishes. The total number of vertebra; was 
one hundred and twenty-three, nearly the same as in the 
monitors, and more than double the number of those in 
the Crocodiles. The ribs had a single head, and were round, 
as in the family of lizards. Of the extremities, sufficient 
fragments have been found to prove that the Mosasaurus, 
