74 Royal Institution. 
long and slender metatarsals, which answer to the second, third, and 
fourth toes. Of the fifth toe there is only a rudimentary metatar- 
sal. The hallux is short, and its metatarsal appears to be deficient 
at its proximal end. 
It is impossible to look at the conformation of this strange reptile 
and to doubt that it hopped or walked, in an erect or semierect 
position, after the manner of a bird, to which its long neck, slight 
head, and small antericr limbs must have given it an extraordinary 
resemblance. 
I have now, I hope, redeemed my promise to show that, in past 
times, birds more like reptiles than any now living, and reptiles more 
like birds than any now living, did really exist. 
But, on the mere doctrine of chances, it would be the height of 
improbability that the couple of skeletons, each unique of its kind, 
which have been preserved in those comparatively small beds of So- 
lenhofen siate, which record the life of a fraction of Mesozoic time, 
should be the relics, the one of the most reptilian of birds, and the 
other of the most ornithic of reptiles. 
And this conclusion acquires a far greater force when we reflect 
upon that wonderful evidence of the life of the Triassic age which is 
afforded us by the sandstones of Connecticut. It is true that these 
have yielded neither feathers nor bones; but the creatures which 
traversed them when they were the sandy beaches of a quiet sea 
have left innumerable tracks which are full of instructive sugges- 
tion. Many of these tracks are wholly undistinguishable from 
those of modern birds in form and size; others are gigantic three- 
toed impressions, like those of the Weald of our own country ; 
others are more like the marks left by existing reptiles or Am- 
phibia. 
The important truth which these tracks reveal is, that at the 
commencement of the Mesozoic epoch bipedal animals existed which 
had the feet of birds, and walked in the same erect or semierect 
fashion. These bipeds were either birds or reptiles, or more pro- 
bably both; and it can hardly be doubted that a lithographic slate 
of Triassic age would yield birds so much more reptilian than 
Archeopteryx, and reptiles so much more ornithic than Compsogna- 
thus, as to obliterate completely the gap which they still leave be- 
tween reptiles and birds. 
But if, on tracing the forms of animal life back in time, we meet, 
as a matter of fact, with reptiles which depart from the general type 
to become bird-like, until it is by no means difficult to imagine a 
creature completely intermediate between Dromeus and Compsogna- 
thus, surely there is nothing very wild or illegitimate in the hypo- 
thesis that the phylum of the class Aves has its root in the Dinosau- 
rian reptiles—that these, passing through a series of such modifica- 
tions as are exhibited in one of their phases by Compsognathus, have 
given rise to the Ratite—while the Carinate are still further modi- 
fications and differentiations of these last, attaining their highest 
specialization in the existing world in the Penguins, the Cormorants, 
the birds of prey, the Parrots, and the song-birds. 
