374 



GENERAL ZOOLOGY 



The muscular system shows many adaptations to the 

 aerial life of the pigeon. The great mass of muscle by which 

 the downward stroke of the wings is accomplished occupies 

 almost all the space on the prominent, keeled breastbone. 

 Its position, low down on the body, makes overturning in 



Skull — ; 



Upper 

 mandible- 



-Cranium 



/Cervical (neck) vertebra 



Ulna 

 Radius 



Thumb 



Lower 

 mandible 



Humerus 

 Clavicles (wishbone)- 

 Coracoid — 



Keel of sternum— 



TJwracic 

 region 



Scapula 



End bone of 

 second finger 



Bone L B<me of 

 of second 

 third finger 

 finger 



-Plowshare 

 bone 



Bone of second toe 



Caudal region 



-—Ankle and foot 

 Bone of first toe 



Fig. 196. Skeleton of pigeon. (Reduced) 



the air almost an impossibility. The muscle which raises the 

 wing is also situated beneath the breastbone, and is inserted 

 on the dorsal surface of the humerus by a tendon which 

 passes through an opening at the shoulder. The tendon thus 

 acts as a pulley in raising the wing. The muscles which 

 bend the toes in perching are so arranged that the mere 

 weight of the bird keeps them contracted, so that even when 

 the pigeon is asleep the toes firmly grasp the perch. 



