316 STEBNA OF WINGLESS BIRDS. 



organisation. The animal has, therefore, the whole 

 of its structure consenting, and not merely consenting, 

 but co-operating in all its actions and all its positions 

 of repose; and it should seem that the posterior 

 extremities of a bird are incapable of supporting the 

 body, so as to make it stable when borne forward in 

 rapid progressive motion, and especially in turning, 

 without the addition of rudimental wings. Thus 

 there is, at least, a harmony and reciprocal action in 

 the parts of the bird, so that while the one assists 

 the other in its operations, it receives assistance in 

 return : as in this instance, the shoulder-joint supports 

 the wing, and the articulation of the wing is necessary 

 to the perfection of the shoulder-joint. This mutual 

 or reciprocal assistance of the parts of an animal to 

 each other is one of the most remarkable points of 

 difference between the mechanics of the living body 

 and of dead matter, and it is one of which we should 

 never lose sight, when we speculate about the former. 

 We have no practical knowledge of a bird with a 

 perfectly immoveable wing, but we have a very near 

 approximation in the emu, which, although a long- 

 legged and swift-footed bird, has its covering, and 

 probably also its food, much more analogous to that 

 of the apteryx than the true ostriches have ; and 

 it is curious also that the two, the one in Australia 

 and the other in New Zealand, are more nearly 

 neighbours, and inhabit climates which are much 

 more nearly similar than those inhabited by the 

 others. On this account we shall, before proceeding 

 to take a very short glance at the comparative struc- 

 tures of the sterna of some of the more remarkable 

 flying birds with reference to their powers of flight, 

 notice that of the emu, as being nearly confined to 

 the supporting of the anterior part of the body. 



