90 THE FLIGHT OF BIRDS 
rise with ease from the ground, they must be able 
first to jump into the £ . Most birds have an active 
springing gait, and are good jumpers, their legs being 
built much in the same way as those of a horse or 
an antelope; the ankle-joint is raised high above 
the ground, and they walk or run upon their toes. 
The springiness is combined with remarkable light- 
ness. The bird’s foot is made almost entirely of 
skin, bone, and tendon; not like the human foot, 
fleshy and full of nerves. It is worked by long 
tendons attached to muscles that spring from the 
top of the leg-bone (the tibio-tarsus) or even from the 
base of the thigh-bone, and, running in grooves under 
the ankle-joint, give to the foot its springiness and 
to the toes their wonderful grip. The fusion of the 
two rows of ankle-bones with their bigger neighbours 
makes the ankle-joint an excellent pulley. Alto- 
gether the bird’s wings have in the legs very able 
assistants. Comparatively few resemble the Swift 
in having very short and feeble legs ; but, as I have 
pointed out above, there are a considerable number, 
mostly big, bulky birds, which, owing to their 
shortness of leg and small power of jumping, have 
difficulty in starting to fly from level ground. 
