256 PHENOMENA OF FLIGHT IN THE ANIMAL KINGDOM. 



Fis. 12. 



have songlit to establish with reft'ard to the relations of the alar surface 

 viitli the length of the great pectora nmscle. 



The inspection of the skeleton furnislies the principal elements of this 

 verification. Passing through that i>art of the zoological collection in 

 the museum which is devoted to the exliibition of the skeletons of birds, 

 you will come away convinced of the relation between the extent of the 

 wing and the length of the great pectoral muscle, as shown in tlie length 

 of tiie sternum. You see by Figs. 10, 11, and 12, how osteology furnishes 

 the necessary proofs of this statement. 



In birds the de- 

 velopment of the 

 bones of the wing 

 gives us a sufti- 

 ciently correct idea 

 of the extent of sur- 

 face presented by 

 these organs when 

 covered with feath- 

 ers. Compare the 

 prodigious length of 

 the fore-arms in the 

 al batross with those 

 of the duck, guille- 

 mot, or diver ; the 

 proportion of the 

 bones will give at 

 the first glance the 

 superiority in re- 

 gard to flight of the 

 albatross in the 

 greater extent of its 

 wings. Comparing 

 the sternum of dif- 

 ferent birds you will 

 find it large, but 

 very short, in the 

 albatross. On the 

 contrary, in the 

 duck, the diver, and 

 the guillemot, tlie 



Skeleton of a penguin, 

 uum very long. 



The wing is very short, and the ster- 



sternum, though narrower, is comparatively very long. The lateral 

 channels, wbich lie on each side of its keel, represent, in one sense, 

 a hollow mold of the pectoral muscles. You can thus verify by the 

 skeletons of hawks and other rapacious birds, the fact that short, 

 thick muscles appertain to large wings ; and by the skeletons of ducks, 

 swans, and diving birds, that small wings possess more slender but 

 larger muscles. This brings us to the considerations which I have pre- 

 viously brought forward. We now see how we can measure the power 

 developed by a flying bird. It is necessary to know the resistance 

 which the air presents to the surface of its wing, and to multiply this 

 resistance for each stroke by the distance which it traverses. Still the 

 problem is not as simple as one might suppose, after this announcement. 

 All tends to the belief that the. rapidity with which the wing strikes the 

 air is not uniform, and that it has increasing and decreasing phases, to 

 which the relative resistance of the air corresponds. To know the exact 



