The Audubon Societies 



SI 



all of the feathers are borne on one bone and the skeleton of the tail is very short. 

 And so we might go on considering each and every part of the bird and we would 

 discover how it has been made as light as its required strength would permit. 



2. Strength: If lightness were the only requirement of the flying-machine, 

 it would be a simple matter to construct one, but, unfortunately, great strength 

 is hkewise required, and it is the combination of the two that is so difficult to 

 achieve. The framework of the machine must be extremely strong to withstand 

 the tremendous strains, and so we find, with the bird, that its framework or 

 skeleton is the most rigid of all animal's. Bones fuse together to get greater 

 strength and are reinforced by the development of new bones from mere bumps 

 or processes to act as props. One cannot fully understand the many beautiful 

 ways in which the bird's skeleton is strengthened unless he has some knowledge 

 of the skeletons of other animals with which to compare it, and so here we can 



A VIRGINIA RAIL, BALANCING ON A FENCE OF FLY-SCREENING, 

 ILLUSTRATING THE SHORT, ROUNDED WING 



merely call attention to the rigidity of the bird's backbone and pelvis, the box- 

 like form of the thorax with the ribs firmly fastened both to the backbone and 

 to the breast bone, and further strengthened by overlapping processes. The 

 familiar 'wishbone' is nothing more nor less than the two collar-bones fused 

 together to give greater strength to the attachment of the wings, and so on. 



If one examines the breast-bone of a bird, he discovers that it is not flat as 

 in man, but has a relatively enormous ridge down the middle for the attach- 



