398 Bird - Lore 



It is the comparative anatomist who helps us see how one group of animals or 

 plants is closely related to or widely different from other groups. By the power 

 of his knowledge of facts, coupled with imagination, this man of science builds 

 what he learns into a wonderful history of life, that far surpasses a story 

 in interest. 



Because he sees things correctly and tells the truth as exactly as he can 

 about what he sees, we should be ready to learn all we may from him. Although 

 we are studying simply nature-study now, we can learn one thing from men of 

 science, namely, to see things correctly and to tell the truth as exactly as we 

 can about what we see. With this suggestion, let us turn to the bird's skeleton 

 and try to discover why it is a help and not a hindrance to the bird in flight, 

 and how it is different from the skeletons of other vertebrates. 



If a horse could fly, as we sometimes read in myths or fairy-stories that it 

 can, it would have great difficulty in managing its heavy head and long legs 

 and tail, to say nothing of steering its long, thick-set body. A horse is built to 

 run and trot and gallop, but not to fly. If a bird could find all of its food in the 

 air, and could nest and rest in air as most fishes do in water, it would scarcely 

 need legs to walk about or hop on, or to help it swim. Since a bird is above all a 

 highly perfected flying-machine, we may expect to find its skeleton put together 

 most conspicuously to suit the purpose of flight, and, at the same time also, 

 the purposes of swimming and walking or hopping. 



The first thing to notice about its skeleton is the lightness of the bones of 

 which it is made; the next thing, the way in which these bones are fitted 

 together for strength, for stability and in some places, for flexibility; and lastly, 

 the thinness of the bones and general compactness of the skeleton as a whole. 

 The bones of a bird are filled with tiny holes, that is, they are porous. This 

 makes them light, and at the same time lets air through them. Some birds 

 have hollow bones, that are filled with air, which adds much to their lightness. 

 It is a curious fact, as you may already know, that certain birds, like the Gulls, 

 for example, which spend so much of their time in flight, do not have hollow 

 bones. The comparative anatomist could help you to understand why this is so. 



In order to understand how bones can be light and even hollow, and yet be 

 put together in such a way as to make a strong, rigid, but flexible skeleton, sup- 

 pose we think of the bird simply as a framework of bones in the shape of a 

 flying-machine. No feathers with bright colors now; no muscles to cover the 

 bones and pull them back and forth into motion; no lungs with big air-sacs to 

 pump in air and expel it to keep the heart beating and the blood circulating, 

 and the muscles working; no brain or spinal cord or nerves to carry messages 

 from one part of the body to the other ; we will think now only of the bones 

 and the way in which they are joined together. 



In the last exercise, we found that if we drew a straight line to represent the 

 backbone of a bird, we could mark off a short space on it for the neck, another 

 short space for the tail, and then by drawing a circle for the skull and two circles, 



