xiv 
CONTENTS 
CHAPTER VI. 
FoRM AND FUNCTION . . 
Digestive apparatus—The heart and circulation—The valves 
of the heart—The blood—Breathing apparatus and pneu- 
matic bones—The process of breathing—Lungs of lower 
vertebrate animals—Regulation of temperature—Problems 
connected with the hollow bones of birds—The kidneys 
—The nerves—The brain—The eye—The ear—The organ 
of voice—Muscles and tendons—Bones—Ligaments— 
Feathers, their structure and development—-Varieties of 
contour feathers—Feather tracts—Moulting—Change of 
colour without moulting—Spurs—The beak—The foot— 
Perching—Swimming. ‘ 
CHAPTER VII. 
FLIGHT 
The wings as levers, the air as fulcram—Horizontal flight—The 
bird in motion, support given by the air—The general shape 
of the bird—Passive machinery—Active machinery—The 
spreading of the wing—Active and passive machinery 
(summary)— Weight of the breast muscles—Movements of 
the wing partly due to the action of the air—The tail— 
Rate of stroke—Phases of the stroke—Figures described 
by the different parts of the wing—The bird’s trajectory— 
Long distance flight—Upward flight—Horizontal and 
gliding flight—Flight in troops—Wind_ and flight—Rising 
with the help of the wind—Soaring—Steering—Stopping, 
use of the bastard wing—Force exerted in flight—Propor- 
tion of wing area to weight in large and small birds— 
Velocity—A note on flying machines—Conclusion. 
CHAPTER VIII. 
THE BIRD WITHIN THE Ecc 
CHAPTER IX, 
YouTH, MATURITY ANDAGE .. . .. Pe ee 
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