ORDER ACCIPITRES. 109 



surface is very extensive, and whose tubes are hollow ; then 

 the arrangement of these same feathers, the form of the wings, 

 convex above and concave beloAV, their firmness, their great 

 extent, and the force of the muscles which move them ; finally, 

 the lightness of the body, the most massive parts of Avhich, 

 such as the bones, are much lighter than those of quadrupeds, 

 for the cavities of the bones in birds are proportionally much 

 greater than in quadrupeds, and the flat bones which have no 

 cavities are much more slender, and less weighty. ' The ske- 

 leton of the onocrotalus,' say the anatomists of the academy, 

 * is extremely light. It weighs but three-and-twenty ounces, 

 though remarkably large.' This lightness of the bones consi- 

 derably diminishes the Aveight of the bird ; and we shall find, 

 in weighing the skeleton of a quadruped with that of a bird in 

 the hydrostatic balance, that the first is specifically heavier 

 than the other." 



We have already observed on the strong and piercing sight 

 of birds, which the extent, elevation, and rapidity of their flight 

 necessarily presuppose. 



" A hawk," says Buffbn again, " sees .from on high a lark 

 upon a clod of earth at twenty times the distance at which a man 

 or a dog can perceive it. A kite having soared to an eleva- 

 tion beyond our ken, can see the small lizards, field-mice, and 

 birds, and select those upon which he chooses to pounce. 

 This great extent of the visual power is accompanied with a 

 precision equally great, for the organ being at once both 

 extremely supple and extremely sensible, the eye grows round 

 or flat, is covered or uncovered, contracts or dilates, and 

 speedily and alternately assumes all the forms necessary to 

 adapt itself to every degree of light or distance. 



" Moreover, the sense of sight being the only one which 

 produces the ideas of motion, the only one by which the degrees 

 of space which are traversed can be compared, and the birds 

 being of all animals the best adapted for motion, it is not 

 surprising that they possess, in the highest degree of certainty 



