82 The Bird 
name to two great divisions of birds: Rati’te (those with 
flat breast-bones, raft-like), including the ostrich, rhea, 
emeu, cassowary, and apteryx; and Carina’te (birds 
with keeled breast-bones, boat-like), including all other 
living birds, whether flyers, as the thrushes, storks, and 
gulls, or swimmers like the penguins. But this differ- 
ence in breast-bones is far from being as profound as 
other differences existing between certain birds which 
are alike in having keels to their sternums. The pres- 
ence or absence of a keel is not of great taxonomic im- 
portance. 
The size of the keel is a pretty sure criterion of the 
flying powers of a bird, that is, Judging not the actual 
duration of flight, but the actual muscular power and 
amount of energy used in flying (Fig. 59). The alba- 
tross, and other birds which, trusting to the air-currents 
to bear them upward, flap seldom and soar much, have 
comparatively smaller keels than do those birds which 
flap their wings more frequently. Thus the pigeon has 
a very good-sized keel; while in the humming-bird this 
bone is enormous, compared to its spread of wings. Dr. 
Frederick A. Lucas has expressed this very graphically 
in a diagram, where it is supposed that the albatross, 
pigeon, and humming-bird have an equal spread of wings. 
On comparison, the keel of the first is seen to occupy but 
a small fraction of the surface of the same bone in a 
humming-bird. To account for this we must realize 
that the wings of the humming-bird execute from six 
hundred to a thousand strokes a minute; while the alba- 
tross may soar for miles with wings held outstretched 
