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MANUAL OF ELEMENTARY ZOOLOGY 



more powerful than the upstroke, which is helped by the 

 fall of the body when the downstroke ceases to raise it. 



The pigeon is a backboned animal, and its structure is on 



the same general plan as that of the frog and 



internal dogfish. It has a chest or thorax, walled by ribs 



Skeleton. and a broad breastbone, but lacks the midriff or 



diaphragm of mammals. It is of the pentadactyle 



type and its skeleton resembles in main outlines that of the 



