392 THE STRUCTURE AND LIFE OF BIRDS chap. 



themselves, were incapable of flight, rely mainly on 

 the following arguments : — 



(i) 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. 1 3 and 34). 



(4) The pelvis is very different from that of the 

 Carinatae. 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 Carinatae, 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 

 Carinatae — e.g. 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. 



