STERNUM OF THE EARED GREBE. 375 



The structure of the shoulder is also well worthy 

 of attention. The form of the clavicle resembles that 

 of birds of prey, both in its curvature of opening and 

 its curvature downwards. The strength arising from 

 these curves is, however, reversed to that of the pre- 

 datory birds. In them the curve of the opening is 

 the more perfect arch, and the bone is flattened in the 

 direction of that arch ; whereas, in the grebes, the 

 lateral .arch, which extends from the angle of the 

 sternal keel to the head of the scapular, is the better 

 formed, and the bone is flattened laterally to give 

 additional stiffness to that. The head of the clavicle 

 also bears against that of the scapular something in 

 the same manner that the arch of a bridge bears 

 against its abutment ; and the scapular, by becoming 

 narrow toward its termination, resists a thrust on the 

 head much better than it resists a pull. 



From this formation of the shoulder, it will be seen 

 that though it forms not an unsteady fulcrum for the 

 action of the wing in flight, it is also well calculated 

 for resisting a strain or pressure from the front ; and 

 from the posterior portion it may be seen that pro- 

 vision is made there for a peculiar action of the feet. 

 The sternal apparatus of the grebe is thus a very 

 typical one ; and when the small and elongated head 

 and neck, and the lobed toes, with the flattened tarsi, 

 turned outwards on their articulations, are taken into 

 consideration, one might almost arrive at a knowledge 

 of the habit of the bird without further investigation. 

 No air-bird, not even the most typical of the falcons, 

 presents the most powerful arch of its clavicle to the 

 air against which it flies, neither has it the extremities 

 of this arch resting on the angle of the keel and the 

 head of the scapula as abutments, as is the case in 

 this bird. Thus it is evident, from the structure of 



