fe is complete. The skin has lost its scales, and the front
limbs are developed into powerful paddles, sometimes six feet in length.
The neck is drawn out until, in some specimens, it is found to consist
of seventy-six vertebrae: the longest neck in the animal world. It is
now doubted, however, if the neck was very flexible, and, as the jaws
were imperfectly joined, the common picture of the Plesiosaur darting
its snake-like neck in all directions to seize its prey is probably
wrong. It seems to have lived on small food, and been itself a rich diet
to the larger carnivores. We find it in all the seas of the Mesozoic
world, varying in length from six to forty feet, but it is one of the
sluggish and unwieldy forms that are destined to perish in the coming
crisis.

The last, and perhaps the most interesting, of the doomed monsters
of the Mesozoic was the Pterosaur, or "flying reptile." It is not
surprising that in the fierce struggle which is reflected in the arms
and armour of the great reptiles, a branch of the family escaped into
the upper region. We have seen that there were leaping reptiles with
hollow bones, and although the intermediate forms are missing, there
is little doubt that the Pterosaur developed from one or more of these
leaping Deinosaurs. As it is at first small, when it appears in the
early Jurassic--it is disputed in the late Triassic--it probably came
from a small and agile Deinosaur, hunted by the carnivores, which relied
on its leaping powers for escape. A flapperlike broadening of the fore
limbs would help to lengthen the leap, and we must suppose that this
membrane increased until the animal could sail through the air, like the
flying-fish, and eventually sustain its weight in the air. The wing
is, of course, not a feathery frame, as in the bird, but a special skin
spreading between the fore limb and the side of the body. In the bat
this skin is supported by four elongated fingers of the hand, but in
the Pterosaur the fifth (or fourth) finger alone--which is enormously
elongated and strengthened--forms its outer frame. It is as if, in
flying experiments, a man were to have a web of silk stretching from his
arm and an extension of his little finger to the side of his body.

From the small early specimens in the early Jurassic the flying reptiles
grow larger and larger until the time of their extinction in the
stresses of the Chalk upheaval. Small Pterosaurs continue throughout the
period, but from