80 THE PASSENGER PIGEON IN PENNSYLVANIA 



the world. When released, fa'r from home, they rise 

 to a great height, hover about for awhile in an un- 

 decided manner, and then they are off like the flight 

 of an arrow on the return trip. 



The pigeons have their larger bones hollow, instead 

 of solid or filled with marrow, like animals, being of a 

 lighter make, combining great strength and surface 

 for muscle leverage with least weight. These hollow 

 bones communicate with airsacs which open in to the 

 lungs, so the hot, rarified air may be forced from the 

 lungs into the hollow bones, thus effecting great buoy- 

 ancy for their bodies as more atmospheric air is 

 consumed in respiration, the dioxide being exhaled, 

 and flight becomes more rapid and easier as they pro- 

 ceed into a long flight. The hollow quills, perhaps, 

 do a like service, as the bones, in assisting buoyancy in 

 proportion to the exertion in the air, making the in- 

 halations more abundant, oxidization rapid, and re- 

 leasing the expanding gasses to charge the cavities, 

 while carbonic acid gas, dioxide, is exhaled, to fall 

 below, being heavier than atmosphere. 



The passenger pigeons were provided with a breast- 

 bone that was large and furnished with a deep keel, 

 affording attachment for muscles of enormous size, 

 which were devoted to drawing the wings forcibly 

 downwards, in lifting strokes, while the conformation 

 of the wings, to give the slight rotary action, so that 

 the feathers beat the air with their flat sides, gave pro- 

 gress and speed, but presented their sharp edges as 

 they returned for another stroke, like an oarsman 



