218 THE POPULAR SCIENCE MONTHLY. 



as this, it might have been said that birds were characterized by the 

 absence of teeth ; but the discovery of a bird that had teeth shows at 

 once that there were ancient birds that, in that particular respect, 

 approached reptiles more nearly than any existing bird does. 



The same rocks have yielded another bird (Ichtltyornis), which 

 also has teeth in its jaws, the teeth in this case being situated in dis- 

 tinct sockets, while those of JSesperornis were not so lodged. The 

 latter also had very small wings, while Ichthyornis has strong wings. 

 Ichthyornis also differed in the fact that the joints of its backbone 

 its vertebrae had not the peculiar character that the vertebrae of 

 existing birds have, but were concave at each end. This discovery 

 leads us to make another modification in the definition of the group 

 of birds, and to part with another of the characters by which they 

 are distinguished from reptiles. We know nothing whatever of birds 

 older than these until we come down to the Jurassic period, and from 

 rocks of that age we have a single bird which was first made known 

 by the finding of a fossil feather. It was thought wonderful that 

 such a perishable thing as a feather should be discovered and nothing 

 more, and so it was ; and for a long time nothing was known of this 

 bird except its feather. But, by-and-by one solitary specimen was 

 discovered, which is now in the British Museum. That solitary 

 specimen is unfortunately devoid of its head; but there is this 

 wonderful peculiarity about the creature that, so far as its feet 

 are known, it has all the characters of a bird, all those peculiari- 

 ties by which a bird is distinguished from a reptile. Neverthe- 

 less, in other respects, it is unlike a bird and like a reptile. There 

 is a long series of caudal vertebrae. The wing differs in some 

 very remarkable respects from the structure it presents in a true 

 bird. In a true bird the wing answers to these three fingers the 

 thumb and two fingers of my hand the metacarpal bones are fused 

 together into one mass and the whole apparatus except the thumb 

 is bound up in a sheath of integument, and the edge of the hand 

 carries the principal quill-feathers. It is in that way that the bird's 

 wing becomes an instrument of flight. In the Archceopteryx, the up- 

 per-arm bone is like that of a bird ; these two forearm bones are more 

 or less like those of a bird, but the fingers are not bound together 

 they are free, and they are all terminated by strong claws, not like 

 such as are sometimes found in birds, but by such as reptiles possess, 

 so that in the Archceopteryx you have an animal which, to a certain 

 extent, occupies a midway place between a bird and a reptile. It is 

 a bird so far as its foot and sundry other parts of its skeleton are 

 concerned ; it is essentially and thoroughly a bird in the fact that it 

 possesses feathers, but it is much more properly a reptile in the fact 

 that what represents the hand has separate bones resembling those 

 which terminate the fore-limb of a reptile. Moreover, it had a long 

 tail with a fringe of feathers on each side. All these cases, so far as 



