326 STERNAL MUSCLES. 



elevating' the wing, or in advancing it, or bending it to 

 the rear, when the bird is in flight. But the actions of 

 these secondary muscles, which are efficient chieflj 

 in altering the direction of the birds in flight, upward, 

 downward, or laterally, cannot be fully explained 

 without more space, and more illustrative figures, 

 than are compatible with the nature, and indeed the 

 purpose, of this brief sketch. The whole of the mus- 

 cular actions of a wing form a very extensive as well 

 as a very nice subject for study, and one which can 

 be very imperfectly comprehended even by those 

 who devote their whole time and their best attention 

 to it. The reason is obi-ious : the actions of the 

 numerous muscles of the wing are so combined with 

 each other, and the action of the one modifies that of 

 the other so much, that the most minute definition, 

 and the most careful study, are incapable of informing 

 us how the wing acts in all its varied motions ; so that 

 the utmost which, in the present state of science, we 

 can expect to obtain, is a very rude and imperfect 

 estimate of the relative powers of wings, derived fully 

 as much from what we see them performing in the 

 living bird, as from any thing apparently more scien- 

 tific (and it is mere appearance rather than reality) 

 which we find in dissecting the dead one. 



In giving a few examples of the form of the sternum, 

 and its apparatus, the coracoids, the clavicle, and the 

 scapulars, as illustrative of the power of flight in birds, 

 we shall not attempt to follow even the outline of a 

 system proposed by M. Lherminier, because that is 

 incomplete, as treating of the sternal apparatus with 

 reference to flight only, and not combining the general 

 character of the class, the support which the body 

 receives from the sternal bones, altogether inde- 

 pendent of power of flight ; and also because, though 



