. The structure and life of birds . sults of the changes that the fore limb hasundergone may now be summed up. (I) It is of most re-markable length. (2) It is at one time rigid, at anotherflexible, according as rigidity or flexibility is with a birds hand a lizards with its wagglyfingers. And how neatly and comfortably the wingfolds, when it is to be put to rest upon the body, in theform of a Z- (3) There are broad surfaces of boneto support the feathers. (4) Strength is combinedwith lightness. (5) The loss of two metacarpal bonesand two fingers has been a gain, since the pre
. The structure and life of birds . sults of the changes that the fore limb hasundergone may now be summed up. (I) It is of most re-markable length. (2) It is at one time rigid, at anotherflexible, according as rigidity or flexibility is with a birds hand a lizards with its wagglyfingers. And how neatly and comfortably the wingfolds, when it is to be put to rest upon the body, in theform of a Z- (3) There are broad surfaces of boneto support the feathers. (4) Strength is combinedwith lightness. (5) The loss of two metacarpal bonesand two fingers has been a gain, since the presenthand formed of three united metacarpals and twounited fingers (I am disregarding the insignificant thumb ) is more efficient for purposes of flight thana hand with five fingers could well be. SKELETONS OF BIRD AND REPTILE 13 The Breastbone and the Bones that meet at the shoulder-joint. A powerful wing would be of no use withoutpowerful machinery for moving it, and a lizard witha birds wings would be no more able to fly than any. Fig. 5.—(a) Sternum of Iguana, with interolavicle, coracoid, precoracoid, , clavicle ; co, coracoid ; icl, interclavicle ; pco, precoracoid ; st, sternum ;(b) Coracoid, scapula, and clavicle of fowl,co, coracoid ; sc, scapula ; cl, clavicle. ordinary lizard. In the birds skeleton the enormousbreastbone suggests a great deal. They must bestrong muscles which have so strong and big a boneto which to attach themselves. No two things canbe more unlike than the breastbones of the bird andthe lizard, and the same may be said of the associatedbones. In the lizard the whole apparatus is flat and i4 THE STRUCTURE AND LIFE OF BIRDS chap. weak. Its chief component, the Sternum (ST, ) or breastbone, is a level expanse with ribsattached to its margin. Down the middle may beseen running a thicker and stronger bone, which throwsout a branch on either side, so that the whole makessomething of a T shape. This bone is called the Inter-clavicle (
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