38 THE STRUCTURE AND LIFE OF BIRDS cuapP. 
been bi-concave, ze. the centra presented hollows 
at either end. This is a form of vertebra found 
in very primitive reptiles, eg., in the Hatteria lizard. 
It is also found in Ichthyornis, a 
f\ fossil bird of more recent date than 
} Archzopteryx. And what is far more 
Seu! strange, the Gull, a highly special- 
~ ised, a thoroughly modernised bird, 
) has some of its dorsal vertebrz con- 
cave behind, thus conforming to an 
old reptilian type, and one almost 
Fic.16.—Vertebra of | Di-concave, which thus carries us back 
Hatteria Lizard. : : ation 
aaa to reptiles of a still more primitive 
c, centrum ; it is am- 
Phiccelous, Ze. con- form.t In teeth, as I hope to show 
cave at each end. ; i ? 
presently, there is nothing unavian. 
It would be very interesting to know how this 
bird lived. Of one thing we may be certain—he 
was a poor flyer. With its three long unconnected 
fingers the wing must have been a weak one. Prob- 
ably he fluttered, rather than flew, from bough to 
bough, his long tail serving as a parachute, and his 
claws may have been used when he was young, 
as Mr. Pycraft has suggested, and also when he was 
moulting, to aid him in climbing, as the young 
Hoatzin uses his now. 
Since the discovery of Archeopteryx the fossil 
bones of many birds of far later date have been found 
in the cretaceous rocks, and also in the rocks of the 
most recent geological periods, the Tertiary and 
{ 
l Sce W. K. Parker on Opisthocomus Cristatus, Proc. Zool. 
Society, vol. xili. part 2. 
