ld have existed in ancient times is a
necessary consequence of the truth of the hypothesis of evolution; and,
hence, the evidence I have laid before you in proof of the existence of
such forms, is, so far as it goes, in favour of that hypothesis.

There is another series of extinct reptiles which may be said to be
intercalary between reptiles and birds, in so far as they combine some
of the characters of these groups; and which, as they possessed the
power of flight, may seem, at first sight, to be nearer representatives
of the forms by which the transition from the reptile to the bird was
effected, than the _Ornithoscelida_.

These are the _Pterosauria_, or Pterodactyles, the remains of which are
met with throughout the series of Mesozoic rocks, from the lias to the
chalk, and some of which attain a great size, their wings having a span
of eighteen or twenty feet. These animals, in the form and proportions
of the head and neck relatively to the body, and in the fact that the
ends of the jaws were often, if not always, more or less extensively
ensheathed in horny beaks, remind us of birds. Moreover, their bones
contained air cavities, rendering them specifically lighter, as is the
case in most birds. The breast-bone was large and keeled, as in most
birds and in bats, and the shoulder girdle is strikingly similar to that
of ordinary birds. But it seems to me that the special resemblance of
pterodactyles to birds ends here, unless I may add the entire absence of
teeth which characterises the great pterodactyles (_Pteranodon_)
discovered by Professor Marsh. All other known pterodactyles have teeth
lodged in sockets. In the vertebral column and the hind-limbs there are
no special resemblances to birds, and when we turn to the wings they are
found to be constructed on a totally different principle from those of
birds.

There are four fingers. These four fingers are large, and three of them,
those which answer to the thumb and two following fingers in my
hand--are terminated by claws, while the fourth is enormously prolonged
and converted into a great jointed style. You see at once, from what I
have stated about a bird's wing, that there could be nothing less like a
bird's wing than this is. It was concluded by general reasoning that
this finger had the office of supporting a web which extended between it
and the body. An existing specimen proves that such was really the case,
and that the pterodactyles were devoid of feath