376 STERNA OF TRCE DIYERS. 



the shoulder alone, and independently of that of the 

 foot, that the grebe is formed for making its way 

 through the water, and not merely along the surface, 

 though the resemblance of the sternum to that of 

 some of the ducks shows that it is also in part a 

 surface swimmer ; and this inference is rendered the 

 more certain by that resemblance being to the ducks 

 of the intermediate division, which have the swimming 

 habit and the diving one in nearly equal perfection. 



2. Sterna of the true Divers. In these birds, the 

 duck-like character which is traceable in the sterna 

 of the grebes disappears ; and while the sternal 

 apparatus presents a still more powerful arch in front, 

 the posterior part of it is continued so as to support 

 more completely the under part of the bird. 



The sternum is long and narrow, a little concave 

 on the upper side, and convex on the under ; the keel 

 well developed, higher in front than the breadth of 

 the side of the sternum, concave in front, and much 

 advanced at the angle ; the under side convex, but 

 less so than that of the sternum, and gradually 

 diminished to the rear, having the middle process, 

 which is broad and rounded, a little flexible. The 

 sides are concave, and have seven or eight ribs on 

 each; and the lateral processes, which are rather 

 slender, and have their terminations curved toward 

 the central one, have the appearance of two short 

 sternal ribs in addition. The anterior lateral pro- 

 cesses are large, and have their points directed upwards ; 

 and the coracoids, which are strong and short, have 

 their bases very much enlarged to the rear, and 

 with large processes projecting in the same direction 

 as the lateral ones. The clavicle is very much curved 

 downwards, with a tubercle at the middle, bearing on 

 the angle of the keel (which is more rounded than in 



