INTRODUCTORY 21 



pressed ! Though birds are essentially flying animals, and though 

 to attain this power they have become profoundly modified as to their 

 bodily shape, they have yet, in some respects, not gone so far as, say, 

 the Bats, for the latter have almost completely sacrificed the power 

 of terrestrial locomotion, while the birds have, with some few excep- 

 tions, preserved this, or, at any rate, they have preserved the hind 

 limbs as " going concerns " of some kind. With this preamble, let 

 us come to closer terms with our subject. And this we can do better, 

 surely, by a study of the bony framework of the body, in its relation 

 to flight, than by any other way. 



Indirectly, of course, the whole body is moulded to bring it into 

 harmony with the requirements of aerial locomotion. The long 

 neck, passing insensibly into the body, which tapers again into the 

 tail ; and the beautifully smooth, rounded surface, formed by the 

 close-fitting overlapping feathers, are very important adaptations to this 

 end, offering the least possible resistance to the air ; while the large 

 mass of the breast-muscles attached to the under surface of the body — 

 which during flight is, as it were, slung between the wings — contribute 

 towards the right ordering of that all-important matter, gravity. 

 In many birds special means have been adopted to secure extreme 

 rigidity, as may be seen by the fact that the separate vertebrae of 

 the back have become welded together to form a stiff, unyielding 

 beam, though in many fliers, as the Parrots, the *' Perching-birds," 

 and Gulls, for example, these vertebrae retain their primitive inde- 

 pendence. But it is not till we come to examine the bones of the 

 shoulder-girdle and sternum, and of the wings that we find the really 

 obvious adaptations or modifications of the skeleton which flight 

 has brought about. 



I will not weary my readers by a long and tiresome comparison 

 between the shoulder-girdle and sternum and fore-limbs of the Reptile 

 and those of the bird, by way of showing how the one became changed 

 into the other, because such a comparison could not possibly carry 

 conviction, except to those who have made a long study of the subject. 

 Let us rather examine the facts as they appear in the bird. By the 

 shoulder-girdle, we may remark, is meant those bones which make 

 up the shoulder-blade, or scapula, the long, straight pillars known 

 as *' coracoids," and the furcula, or '' merry-thought." These form 



