40 THE BONES. 



for retaining air, have been observed to suffer 

 severely, as was proved by a Mr. Robertson, who 

 took two birds up with him in a balloon, one of 

 which actually died at the height of 15,600 feet; 

 whereas, others better provided with air-cells appear 

 to feel no such inconvenience. 



Mont Blanc, the most elevated mountain in 

 Europe, is not quite three miles high; and yet on 

 the top, breathing is extremely difficult; nevertheless, 

 the Condor of South America, the largest bird gifted 

 with the power of flight, will dart upwards suddenly 

 from the deepest valleys to a considerable height 

 above the summit of even the lofty mountain of 

 Chimboraco, w r hich is one-fourth part higher than 

 Mont Blanc. Humboldt, the celebrated traveller, 

 who has given the best account of those regions, 

 says, that he has frequently seen this enormous bird 

 soaring without an effort, and enjoying itself at an 

 elevation much higher than that of the clouds in 

 our atmosphere. 



In tracing the bones of the skeleton down the 

 back, another remarkable difference is perceptible. 

 In men and animals, the whole back-bone is more or 

 less moveable, and can be bent ; whereas, in birds, 

 the parts more immediately connected with the 

 back, are either altogether consolidated or stiffened, 

 so as to allow little or no play in the joints. In 

 carving a fowl or any other bird at table, this pecu- 

 liarity may easily be remarked. The want of 

 motion in the back, however, is amply compensated 

 by a greater number of bones in the neck, and 

 greater power of moving them, which enables birds 

 to turn their heads in all directions, with extra- 



