Arms and Legs 91 



of the obvious differences in the functions or uses of these 

 organs. It would be entirely too far-fetched to say that the 

 flipper of a whale is constructed on the same plan as the arm 

 of a man because either represents an ideal pattern for 

 the arm. 



Bone for bone, there is homology between front limbs 



Fig. 23. Homologies among the Limbs of the Differ- 

 ent Classes of Vertebrates 



Walking, crawling, swimming, flying — all the various modes of loco- 

 motion found among the five classes of backboned animals — are carried 

 on by variations of the same fundamental structures. Hind limbs in upper 

 row, with varying positions of the heel, H; fore limbs in lower row, with 

 varying positions of the wrist, W. a, frog; b, lizard; c, bird; d, horse; 

 e, hippopotamus; /, elephant; g, man; h, bat; /, dolphin; k, blackfish. 

 From Gruenberg, Biology and Human Life, published by Ginn & Company. 



and hind limbs. Excepting the fins of fishes, which are not 

 so highly specialized, the limbs of one class of backboned 

 animals corresponds to the limbs of other classes of back- 

 boned animals, whether they live on land or in the water, in 

 the air or in caves or underground. 



Similar correspondence in detail, in apparent defiance of 

 diverse modes of living, extends among the vertebrates to 



