CHAPTER III 



THE CARINATE OR KEEL-BREASTED BIRDS, AND 

 THEIR CHIEF PECULIARITIES 



The birds to which the rest of this volume is to be devoted all differ 

 from the Ostrich tribe, not only in regard to certain peculiarities 

 in the formation of the skull, but also in that the breast-bone bears 

 a deep plate, or '' keel," which runs down the middle of its under 



Shoulder^ blade 



Merry = 

 thought 



Breast = bone 



Keel 



Fig. 12.— The shoulder=girdle of a carinate bird to show the keel of the 

 breast=bone, the large merry=thought, and separate blade=bone. 



surface. In addition to this, the bones which are charged with the 

 support of the wings are different, not in kind, but in degree ; and 

 this because, with the loss of the power of flight which we remarked 

 in the Ostrich tribe, these " shoulder-girdle " bones, as they are 

 called, degenerated. As a consequence, the blade-bone became 

 Immovably fixed to its supporting pillar, the *' coracoid " ; and 



