stal Part of
Metacarpus.

A, Metacarpal bone; B, first phalanx; C, second phalanx, D, third
phalanx; E, distal sesamoid bone; 1, volar pouch of capsule of fetlock
joint; 2, inter-sesamoidean ligament; 3, 4, proximal end of digital
synovial sheath; 5, ring formed by superficial flexor tendon; 6, fibrous
tissue underlying ergot; 7, ergot; 8, 9, 9', branches of digital
vessels; 10, distal ligament of distal sesamoid bone; 11, suspensory
ligament of distal sesamoid bone; 12, 12', proximal and distal ends of
bursa podotrochlearis. (From Sisson's "Anatomy of the Domestic
Animals").]

The first phalanx (os suffraginis) normally sets at an angle of about
50 to 55 degrees from a horizontal plane while weight is being
supported. Its distal end articulates with the second or median phalanx
(os corona) and forms the proximal interphalangeal (pastern or
suffraginocoronary) joint. This also, is a ginglymus joint, having but
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 w