96 The Bird 



of a hummingbird or a grouse require than do the slowly 

 flapping pinions of a gull or an albatross. When we 

 compare the relative shortness of the upper arm-bone, 

 or humerus, in the former groups with the long wing- 

 bones of the sea-birds, we again realize what exquisite 

 adaptations exist everywhere in Nature. 



The proportionate length of the various parts of the 

 fore limb of a bird forms an interesting coiollary to its 

 habits of life. For example, the hand in penguins and 

 in hummingbirds is very long indeed; while in the os- 

 trich the humerus is considerably longer than the fore- 

 arm and hand combined. (Compare Figs. 269 and 272.) 



Before we leave the wing-bones, it will be well worth 

 our time to consider for a moment how limbs first origi- 



....., . . ...... . 



-^mmiim^ 



^^iiVV;---- ' * 



FIG. 72. Diagram showing the origin of paired fins (limbs) from a continuous 

 fin-fold. (After Wiederscheim.) 



nated. In the lowest of fishes, such as our friend the 

 Amphioxus and in lampreys, limbs are altogether absent, 

 but in embryos of sharks we get a hint of what the first 

 ^reat fish-like forms were like. Along the lower part of 

 each side of the body there runs a continuous fin, so that 



