1 K L). 



457 



make the horizontal spine stable upon two legs with- 

 out the addition of a rudimental wing 1 . Thus there is 

 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 more 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 forms of flight, 

 notice that of the emu, as being nearly confined to 

 the supporting of the anterior part of the body. 



This sternum is oval, without any keel, and bears 

 some resemblance to the breast-plate of a tortoise ; 

 and t'he coracoids, whose principal use is to support 

 the bone, and preserve the form of the anterior part 

 of the chest against the weight of the bird, the pre- 

 sence of the atmosphere, and casualties, without 

 having any direct strain to bear when the bird is in 

 motion, are short, broad, and flat. 



The following figure is a side view of this sternal 

 apparatus. 



The outline of the sternum of this bird is, it will be 

 seen, very convex, with merely a trace of a keel at the 

 anterior part, near the junction of the coracoids. 

 The ribs are articulated far forward, and they are 

 much thicker ;m<l stronger than in flying birds. There 

 is not, upon this bony structure, any placo where 



muscles capable of giving motion to a wing could be 

 inserted. The strong articulation by the coracoids 

 and the ribs, and the length of the scapulars which 

 suspend the former, enable this form of bone, how- 

 ever, to give the most efficient support to the body, 

 as a basket in which the thoracic viscera are carried ; 

 and its convex form renders it a most efficient breast- 

 plate against any external injury to which the bird 

 may be exposed. 



Those who consider flight as the essential charac- 

 teristic of birds, sometimes regard this structure as an 

 imperfect, one ; but when we examine it with regard 

 to the offices which it has to perform, we find the 

 same perfection of adaptation in it as in that form 

 which affords a fulcrum to the most active wing, and 

 insertion to the most powerful muscles. The species 

 of land birds incapable of flight are so few, and their 

 natural pastures on the earth so peculiar and so 

 limited, that we can with difficulty so connect them 

 with the rest of nature as to understand the part 

 which they act in the general economy. But though 

 they are thus, in a great measure, a sealed book to us, 

 we find that, in as far as we can study them with 

 relation to their haunts, they afford as irresistible evi- 

 dence of that perfect knowledge of all the circum- 

 stances, at the original formation of the creature, 

 which inscribes the name of God upon all that God 

 has made, in characters so plain that he who runs may 

 read, as any other race that can be named. The 

 ostrich on the arid expanse of the African karoo, the 

 nhandu among the tall herbage of the American 

 pampas, the emu on the "hummocky" plains of Austra- 

 lia, and (as we have reason to suppose) the apteryx 

 by the shingly bases of the New Zealand cliffs, are 

 all as much in harmony with the scenes in which we 

 find them, as the parrot is with the perennial bloom 

 of the tropical forest, or the albatross or the petrel is 

 with the expanse of the world of waters. Wings are 

 not wanted upon extended flats of firm surface ; they 

 are for the " ups and downs" of feeding grounds ; 

 and, therefore, those birds to which wings would be an 

 incumbrance have them not, but in their stead organ- 

 isations better suited to their haunts. 



Sterna of winged Birds. In considering the. sterna 

 of birds as indices to their different powers of flight, 

 the elevated crest or keel is certainly the most im- 

 portant ; while of the other bones which form part 

 of the sternal apparatus, the most important is the 

 clavicle, for as we have seen the coracoid bones are 

 constant, not very much dependent on the rate or 

 style of flight, and the scapulars, though of weaker 

 structure, and less fitted for bearing cross strains, are 

 often more developed in birds which fly heavily tha r i 

 in those which fly well. 



But still the form and consistency of the sternal 

 bone itself, independently of its ridge or its appen- 

 dages, vary considerably in birds of different powers 

 of wing. The firmer the sternum is, that is, the more 

 completely that it consists of one plate of bone, with- 

 out apertures, and with the different pieces in whic 

 ossification begins in the young birds, united by 

 bone, the bird flies the better and the more power- 

 fully ; and of course, in proportion as the sternum is 

 deficient in those qualities, the flight of the bird is 

 less elevated and less capable of being continued. 

 If the sternum, besides being of solid bone, is of 

 considerable breadth, and curved in its section as 

 well as in the principal line of its crest, the bird is 



