22 6 BACKBONED ANIMALS. 



position of the knee is seen at k ; then follows the foot, f % 

 or tarso-metatarsus, that in wading birds is very long, and 

 in powerful fliers, as the man-of-war hawk (Fig. 283), very 

 short. The heel, h, is far from the ground, and to the 

 foot-bone are attached the two, four, or five toes, as the 



FIG. 268. Skeleton of a sparrow. ^, quadrate bone, peculiar to reptiles 

 and birds and some amphibia ; #, breast-bone ; m, merry-thought or 

 collar-bone ; c, coracoid bone, over which the tendon works to pull up 

 the wing ; /, plowshare-bone, on which the tail grows. Wing-bones : 

 a, upper arm ; e, elbow ; /a, fore-arm ; w, wrist ; /, thumb ; /ia, hand. 

 Leg-bones : M, thigh-bone ; k, knee ; /, lower part of leg ; h, heel ; /, 

 foot. 







case may be, that are armed with scratching or clinging 

 claws that extend in different directions. Generally there 

 are three before and one behind, as in* Fig. 268 ; others 

 have two before and two behind, or, as in the swifts, all 

 four extend to the front. To prevent birds from falling 

 while asleep on a perch, there is a wonderful arrangement 



