What is "small pastern bone"

Pastern \Pas"tern\, n. [Of. pasturon, F. p[^a]turon, fr. OF. pasture a tether, for beasts while pasturing; prop., a pasturing. See Pasture.]

1. The part of the foot of the horse, and allied animals, between the fetlock and the coffin joint. See Illust. of Horse.

   Note: The upper bone, or phalanx, of the foot is called the great pastern bone; the second, the small pastern bone; and the third, in the hoof, the coffin bone.

   Pastern joint, the joint in the hoof of the horse, and allied animals, between the great and small pastern bones.

2. A shackle for horses while pasturing.
   --Knight.

3. A patten. [Obs.]
   --Dryden.