392 THE STRUCTURE AND LIFE OF BIRDS CHAP. 
themselves, were incapable of flight, rely mainly on 
the following arguments :— 
(1) The breastbone has no keel. There is no sign 
of one even in the embryo Ostrich. 
(2) The clavicle is only rudimentary: in the Casso- 
wary it almost vanishes as the bird grows to maturity ; 
in the Emeu it persists in a much reduced state. 
(3) The coracoid and scapula make a much larger 
angle than in birds that fly (pp. 13 and 34). 
(4) The pelvis is very different from that of the 
Carinate. Except in the Rhea and the Cassowary, 
the‘ilium and ischium do not unite behind the thigh 
joint. 
(5) The seams between the different bones of the 
skull persist much longer. 
(6) Most of the feathers have no barbicels or 
hooklets. This really tells the other way, as I hope 
to show. 
(7) There are, as it is maintained, no apteria or 
featherless tracts. 
On the other side we have these arguments: 
(1) In some of the Carinate, for instance in the 
Rails, the keel is much reduced, apparently reverting 
to a less developed state. The protuberance of the 
Rhea’s rounded breastbone is not unlike a rudi- 
mentary keel. 
(2) The clavicles are much reduced in some of the 
Carinate—eg. in some Woodpeckers. In some of the 
Parrots the two bones do not even meet. 
(3) The angle made by the coracoid and scapula 
varies very much in different species of the keel-less 
birds. Hence this point does not count for much. 
