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 couollary 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- 
Fic. 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 
great fish-like forms were like. Along the lower part of 
each side of the body there runs a continuous fin, so that 
