156 THE UNIVERSITY OF THE STATE OF NEW YORK 



have transferred their labors to the bird's gizzard so that the jaws 

 may be very light, and there are no teeth. The head is rela- 

 tively small and the legs are slender. The body is covered with 

 buoyant feathers and there are air sacks connected with the 

 lungs that add to the buoyancy of the bird's body. Compactness 

 is brought about by shortening the body and fusing the verte- 

 brae ; by firmly fastening the ribs to the breastbone as well as to 

 the backbone and furnishing them with interlocking processes. 

 The heavy muscles that move the wings and legs have been 

 moved toward the center of equilibrium, those of the wings to 

 the breastbone and those of the legs to the thighs. Only the 

 tendons are found on the outer joints of wings and legs. The 

 tail vertebrae are much shortened and fused to form one bone, 

 the pygostyle, upon which the feathers are borne. The heavy 

 internal parts like the heart, liver, gizzard and intestines are like- 

 wise moved toward the center of equilibrium and all are hung 

 beneath the wings much as the body of an airplane is supported. 

 This compactness adds to the bird's strength and permits of 

 the attachment of the huge masses of muscle to the breastbone 

 for manipulating the wings. The bird's feathers are said to be 

 the strongest substances of their size and weight in the world. 



1 Structure 



Skeletoh of a fowl Nu 4 



Examine the skeleton of the fowl with regard to the above 

 points. 



a The wings 



Topography of a bird Nu 2 



The bird's arms are its wings, similar to man's except that the 

 bones of the wrist and hand have become fused for strength. 

 Only the thumb, first and second fingers have been preserved and 

 only the first finger is important. On the fused hand are borne 

 the longest flight feathers called the primaries; on the forearm 

 are borne the next longest flight feathers called the secondaries. 

 The few long feathers lying next to the body when the wing is 

 extended are borne on the upper arm and are called the tertiaries. 



Black-crowned night heron Nu HeB5 



Examine the spread wing and classify the feathers 



