BIRDS CONQUEST OF THE AIR 



739 



Chap. 36 



ing for danger, feeding, and nest building. The remainder of the vertebral 

 chain is rigid except for four or five caudal vertebrae which allow the tail to 

 act as a rudder during flight. The terminal bone, called the ploughshare or 

 pygostyle, is composed of "fused vertebrae supporting the tail. It is a great 

 contrast to the long tail (20 vertebrae) of the earliest known bird, Archae- 

 opteryx (Fig. 36.20). 



The shoulder girdle supplies the sockets for the wings and with the keeled 



Shoulder 

 Wing 



Clovicle 

 wish bone 



Keel 

 pectoral 



rdle 



Torso- metatarsus 



Fig. 36.10. Skeleton of a bird (domestic fowl). The main skeleton of birds is 

 built for locomotion in the air and on land (or water). No other animals are so 

 perfectly adapted to travel in such different surroundings. The flexibility of the 

 vertebral column is almost solely limited to the neck whose turning makes it pos- 

 sible for a bird to see in every direction, and the tail which is a rudder. The 

 pectoral girdle, chiefly its keel, is concerned with air travel. The keel serves for 

 the attachment of the flight muscles, the "white meat" of domestic fowl, the rela- 

 tively huge pectoralis major muscle that lifts the wings, and the smaller pectoralis 

 minor that lowers them. The pelvic girdle or saddle is concerned with land travel. 

 Its irregular plates (pelvis in the figure) serve for the attachment of the leg 

 muscles; those of the "drumsticks" (dark meat) are as important to walking as 

 the pectoralis muscles are to flying. (Courtesy, Putnam: Animal X-Rays. New 

 York, G. P. Putnam's Sons, 1947.) 



