202 BIOLOGY FOR BEGINNERS 



Lightness, hollow bones, air sacs, feathers, beak. 

 Feathers. 



Origin, modified, scales (other epidermal structures). 

 Distribution, tracts. 

 Kinds, down for warmth. 

 Regular feathers for outline. 

 Quill feathers for locomotion. 

 Structure. 



(1) Vane, barbs, barbules, hooks. 

 Advantages: lightness and case of repair. 



(2) Rachis, grooved for strength. 



(3) Quill, hollow for strength lightness. 

 Shape, one sided for " feathering." 



Uses, flight, contour, warmth, color, to shed water. 

 Moulting, for repair replacement and color change. 

 Wing, homologous to hand, not analogous. 

 Bones, three shoulder bones in tripod form. 

 Shoulder blade, narrow. 

 Collar bone (wish bone) united. 

 Coracoid, to breast bone, special for flight. 

 Arm bones long and slender. 

 Hand reduced to three fingers (why?). 

 Muscle power. 



Muscles not on wing (why ?), cf. human hand. 

 Breast muscles one-third weight. 

 Outer and inner layers (white meat). 

 Large ridge on breast bone. 

 Tendons and pulleys at shoulders. 

 Shape of wings. 



Feather arrangement, why longest feathers at end? 

 Concave below, flexible rear edge and tip. 

 2. Adaptations for active life. 



Much energy, oxidation, food, food-getting, digestion, respira- 

 tion, circulation, excretion. 

 Digestion. 



Crop for storage, flockwise feeding. 

 Gizzard for grinding in place of teeth (why?). 

 Powerful digestive fluids. 

 Respiration. 



Lungs finely cellular (why?). 

 Air sacs for reserve air, air in bones. 

 High rate of breathing and temperature. 

 Excretion via lungs. 

 Use of air in song, location of syrinx. 

 Circulation. 



Heart large, four chambered, rapid beat. 

 Blood vessels, large, especially to breast. 



