52 Bird - Lore 



ment of muscles, the familiar breast muscles or white meat of the fowl. These 

 are the powerful muscles that manipulate the wings, relatively hundreds of 

 times more powerful than the similar muscles in man. 



3. Compactness: A third requisite of a iiying-machine is compactness, 

 the heavier parts must all lie close to the center of gravity. There must be no 



A BLUEBIRD IN FLIGHT, ILLUSTRATING THE WING OF AVERAGE PROPORTIONS 

 ADAPTED TO THE NORMAL METHOD OF FLIGHT 



great weight on the wings or the tail or it will not be steady. This is most 

 strikingly accomplished in the bird. We have already spoken of the shortening 

 of the tail, the loss of teeth and heavy parts of the head, and the location of the 

 flight muscles on the breast-bone instead of on the wings. These are all adapta- 

 tions, not only to make the bird lighter, but also to bring the weight close to the 

 center of gravity. What is true of the wings is likewise true of the legs. Birds 

 do not have fat calves. Most of the muscles are on the upper leg close to the 

 body, and, when necessary, they are prolonged to the tips of the toes as very 

 light tendons, just as is done in the wings. The body itself is short and deep 

 for the same reason of bringing the heavy liver, gizzard, and intestines as close 

 to the center of gravity as possible. 



4. Power: A fourth requisite of a machine that will fly is power. Until 

 gasoline was discovered and the gasoline engine, flight was impossible because 

 the known engines and fuels were all too heavy. Great advance has been made 

 in recent years in improving the engines, making them lighter and more powerful 

 for the amount of fuel used, but still the great problem and the greatest draw- 

 back to long-continued flights is the weight of the fuel. An aeroplane can carry 



