STERNA OF ACCIP1TRES. 327 



very ingenious and scientific so far as it goes, the 

 sketch which he gives is not perfectly satisfactory, 

 even in so far as the mere action of flying is con- 

 cerned. The sternum and the sternal apparatus, 

 whether of bones or of muscles, are not the whole 

 organs of flight, we have still to take into account 

 the bones and muscles of the wing, and the character 

 of the feathers with which that wing is furnished ; 

 and even if we were put fully in possession of these, 

 there still remains the accordance of the other struc- 

 tures of the bird with the entire wing, as relates to 

 the style of flight, and also to those other actions of 

 the bird with which the flight is always in accordance. 

 In consequence of these difficulties, which volumes 

 of writing would not explain away, we must content 

 ourselves with a few short notices of the sternal 

 apparatus of the leading division of birds, as formed 

 on the usual mixed characters. 



STERNA OF THE ACCIPITRES. 



In this class, the sternum is firm, though the 

 thicker parts of it are full of air-cells, more especially 

 the enlarged base of the keel, which passes, by a 

 gradual curvature, into the surface of the sides of the 

 sternum, without any corresponding cavity on the 

 upper side, or side toward the interior of the bird. 

 Its form is nearly that of a parallelogram, with the 

 length exceeding the breadth, concave on the upper 

 side, and convex on the under. The keel generally 

 large and elevated, but always lower the broader 

 the sternum is in proportion to its length. The 

 anterior margin of the keel is concave, and the 

 under one convex : the anterior angle sometimes 

 even with the anterior part of the bone, and sometimes 

 in advance of it, with the edge thickened, as if it con- 



