All this horny part that a bird stands up on is its foot.

And the top of it, nearest to the feathers, is the heel.

Don't you see, when I bend the foot _so_," continued the Doctor, as he bent the Sparrow's foot forward, "that the top of the horny part makes a joint that stands out backward, in the same position your heel always has?
All this slender horny part of the foot, above the roots of the toes, corresponds to the instep of your foot, and of course the heel comes next.

You must remember the name of it--the Wise Men call it the _tarsus_." "Then hasn't a bird got any legs, Uncle Roy, only just feet ?" asked Dodo.
"Oh! yes; legs too, with a knee-joint and a hip-joint, like ours.

But all these parts are up closer to the body, and hidden by the feathers, so that you cannot see them." As the Doctor said this there was a great commotion.