n the Solenhofen slates, was a
bipedal animal. The parts of this skeleton are somewhat twisted out of
their natural relations, but the accompanying figure gives a just view
of the general form of _Compsognathus_ and of the proportions of its
limbs; which, in some respects, are more completely bird-like than those
of other _Ornithoscelida._

Fig. 7.--Restoration of Compsognathus Longipes

We have had to stretch the definition of the class of birds so as to
include birds with teeth and birds with paw-like fore limbs and long
tails. There is no evidence that _Compsognathus_ possessed feathers;
but, if it did, it would be hard indeed to say whether it should be
called a reptilian bird or an avian reptile.

As _Compsognathus_ walked upon its hind legs, it must have made tracks
like those of birds. And as the structure of the limbs of several of the
gigantic _Ornithoscelida,_ such as _Iguanodon,_ leads to the conclusion
that they also may have constantly, or occasionally, assumed the same
attitude, a peculiar interest attaches to the fact that, in the Wealden
strata of England, there are to be found gigantic footsteps, arranged
in order like those of the _Brontozoum,_ and which there can be no
reasonable doubt were made by some of the _Ornithoscelida,_ the remains
of which are found in the same rocks. And, knowing that reptiles that
walked upon their hind legs and shared many of the anatomical characters
of birds did once exist, it becomes a very important question whether
the tracks in the Trias of Massachusetts, to which I referred some time
ago, and which formerly used to be unhesitatingly ascribed to birds, may
not all have been made by ornithoscelidan reptiles; and whether, if we
could obtain the skeletons of the animals which made these tracks, we
should not find in them the actual steps of the evolutional process by
which reptiles gave rise to birds.

The evidential value of the facts I have brought forward in this Lecture
must be neither over nor under estimated. It is not historical proof of
the occurrence of the evolution of birds from reptiles, for we have no
safe ground for assuming that true birds had not made their appearance
at the commencement of the Mesozoic epoch. It is, in fact, quite
possible that all these more or less avi-form reptiles of the Mesozoic
epochs are not terms in the series of progression from birds to reptiles
at all, but simply the more or less modified descendants of Palaeozoic
fo