374 



STERNUM OF THE EARED GREBE. 



curved form of the clavicle, all indicate considerable 

 action of the wings. Its stoutness and firmness in the 

 posterior part also indicate considerable action of the 

 legs, not of the tarsi merely, but also of the tibiae, 



and not in the vertical plane, as in the common 

 operation of walking, but in a direction contrary, or 

 at all events oblique, to that plane. A sternum which 

 best suits for a walking motion is that which has the 

 posterior angles taken off, so that the whole has a 

 lozenge shape, as in poultry and pigeons; and one 

 which answers best for the alternate foot motion of 

 swimming on the surface of the water is of a punt 

 or boat shape, which bears up the body equally. But 

 the sternum of the grebe does not answer to any of 

 these characters : it is shortened, as in the birds of 

 prey, to admit a free motion of the legs, and the 

 lateral processes backward are formed into a sort of 

 strong, yet partially flexible arches, for defending the 

 ides of the bird. 



