226 BACKBONED ANIMALS. 
position of the knee is seen at £ ; then follows the foot, /, 
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, 4, is far from the ground, and to the 
foot-bone are attached the two, four, or five toes, as the 
Fic. 268.—Skeleton of a sparrow. g, quadrate bone, peculiar to reptiles 
and birds and some amphibia; 6, breast-bone; , merry-thought or 
collar-bone ; ¢, coracoid bone, over which the tendon works to pull up 
the wing; 2, plowshare-bone, on which the tail grows. Wing-bones: 
a, upperarm; e, elbow; /a, fore-arm; w, wrist; ¢, thumb; 4a, hand. 
Leg-bones: #4, thigh-bone; 4, knee; /, lower part of leg; 2, 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 
