Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/173

 Rh 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 Crocodile, but resembled the Iguanas, in having an apparatus of teeth fixed on the pterygoid bone, (Pl. 20, k.) 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 vertebræ 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 are essential to support the back of animals that move on land: in this respect, they agree with the vertebræ of Dolphins, and were calculated to facilitate the power of swimming; the vertebræ of the neck allowed to that part also more flexibility than in the Crocodiles.

The tail was flattened on each side, but high and deep in the vertical direction, like the tail of a Crocodile; forming at straight oar of immense strength to propel the body by horizontal movements, analogous to those of skulling. Although the number of caudal vertebræ was nearly the same