The movement practically all occurs at the radio-carpal and intercarpal joints, the articular surfaces of which are widely separated in front during flexion, but remain in contact behind. The distal row remains in contact with the metacarpus. The intermediate and ulnar carpals move together as one piece, but the radial does not move so far as the intermediate, so that the anterior and interosseous ligaments connecting these bones become tense and oblique in direction. THE FETLOCK JOINT This, the =metacarpo-phalangeal articulation= (Articulatio metacarpo-phalangea), is a ginglymus formed by the junction of the distal end of the large (third) metacarpal bone, the proximal end of the first phalanx, and the proximal sesamoid bones. =Articular Surfaces.=—The surface on the large metacarpal bone is approximately cylindrical in curvature, but is divided into two slightly unequal parts by a sagittal ridge. This is received into a sort of socket formed by the first phalanx below and the two sesamoids together with the intersesamoid ligament behind. The latter is a mass of fibro-cartilage in which the sesamoid bones are largely embedded. It extends above the level of the sesamoids, and is grooved to receive the ridge on the metacarpal bone; its posterior surface forms a smooth groove for the deep flexor tendon. [Illustration: FIG. 148.—SAGITTAL SECTION OF DISTAL PART OF LIMB OF HORSE. _1_, Large metacarpal bone; _3_, fetlock joint; _4_, proximal sesamoid bone; _5_, first phalanx; _6_, pastern joint; _7_, second phalanx; _8_, coffin joint; _9_, third phalanx; _10_, distal sesamoid (navicular bone); _12_, suspensory ligament; _14_, deep flexor tendon; _15_, superficial flexor tendon; _16_, posterior annular ligament of fetlock; _20_, inferior sesamoidean ligaments; _21_, extensor tendon; _24_, plantar cushion; _25_, periople; _28_, wall of hoof; _29_, sole of hoof; _A_, navicular bursa, proximal part. (After Ellenberger-Baum, Anat. für Künstler.) ] [Illustration: FIG. 149.—ARTICULAR SURFACES OF FIRST PHALANX AND SESAMOIDS AT FETLOCK, WITH INTERSESAMOID AND SUSPENSORY LIGAMENTS. (After Schmaltz, Atlas d. Anat. d. Pferdes.) ] The =joint capsule= is attached around the margin of the articular surfaces. It is thick and ample in front; here a bursa is interposed between it and the extensor tendons, but the tendons are also attached to the capsule. Posteriorly it forms a thin-walled pouch which extends upward between the metacarpal bone and the suspensory ligament about as high as the point of bifurcation of the latter. The capsule is reinforced by two lateral ligaments.