xxxvi INTRODUCTION 



The whole body is brought into harmony with the 

 requirements of flying. The long neck, passing in- 

 sensibly into the body, which tapers again into the 

 tail; and the beautifully smooth, rounded surface 

 formed by the close-fitting overlapping feathers, offer 

 the least possible resistance to the air; while the large 

 mass of the breast-muscles attached to the under sur- 

 face of the body — which during flight is, as it were, 

 slung between the wings — contribute toward the right 

 ordering of that all-important matter, balance. 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. But it is 

 not until we come to examine the bones of the shoul- 

 der-girdle and sternum, and of the wings, that we find 

 the modifications of the skeleton which flight has 

 brought about. 



By the shoulder-girdle 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 a sort of cage fixed 

 on to the front of the sternum, or breast-bone. This 

 bears, as everybody knows, a rough resemblance to 

 the hull of a ship, with an extremely deep keel. A 

 reference to the figure her.e should make this clear. 

 The deep keel and the broad, flat plate of the breast- 

 bone serve for the attachment of the breast-muscles, 

 which in the bird are of enormous size, equalling or 

 exceeding in weight all other muscles of the body. 



These muscles, which constitute the large mass of 

 flesh familiar to every one as the "breast-meat" of a 



