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, w^e again realize what exquisite 

 adaptations exist ever3'where 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 Jiow limbs first origi- 



f ^"^ nuv ......•.....•■.-.•■••..- ..■..■■■■.. r..i:^i^^^^0^^^^^^ 



'^■yy.<-y-:-:'.-y/\Ly ■)»>?•;•?•?? \,''A\<w/,'/f^, 



~.;.;>UA.;»......J "IS&l^i;^^}^:- 



Flu. 72. — Diagram showing the origin ot paired fin.s (Hmbs) 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 



