slight lateral motion, and that only when it is in a state of flexion. A
rather broad articular surface--from side to side--exists here,
lessening the strain on the collateral ligaments somewhat. Dorsal
flexion is checked by the flexor tendons and dorsal ligaments. Volar
flexion is restrained by the extensor tendons.

The distal end of the second phalanx (os corona) has but slight lateral
motion and this is manifested principally when it is in a state of volar
flexion. Undue dorsal flexion is prevented by the deep flexor tendon
(perforans) and volar flexion is inhibited by the extensor of the digit
(extensor pedis). Thus it is seen, that when the leg is a weight-bearing
member, weight is supported by the bony framework whose constituent
parts are joined together by ligaments and tendons and each one of the
several bones articulates in such manner that the joint is locked. The
articular parts of bones rest upon or against an inhibitory apparatus,
and are slightly flexed, as in the carpus, or considerably flexed such
as in the fetlock joint when weight is being supported. In the first
instance, for example, the flexors of the carpus and the superior check
ligament assisted by the flexors of the phalanges constitute the
inhibitory apparatus.

It will be noted that provision for weight bearing is so arranged that
muscular energy is not required except in the matter of suspension of
the body between the scapulae and here tonic impulses only are necessary
to maintain an equilibrium[6], yet in every instance where weight is not
supported by bones, inelastic ligaments or tendinous structures relieve
the musculature of this constant strain. This explains the fact that
some horses do not lie in the stall, yet in spite of their constant
standing position, they are able to rest and sleep.