(_b_) There is but one tendon sheath in the foot—the sheath common to the two flexor tendons (great sesamoid sheath). It encloses the flexor tendons from the middle third of the cannon down to the middle of the short pastern, and is intimately united with the flexor pedis perforans tendon (Fig. 17, _f_, _f′_, _f″_, _f‴_. Fig. 18, _d_, _d′_, _d″_, _d‴_). [Illustration: FIG. 17. Right forefoot seen from the external side; _f_, _f′_, _f″_, _f‴_, great sesamoid sheath (tendon sheath); _g_, mucous bursa beneath anterior extensor tendon of the toe; _h_, mucous bursa beneath extensor tendon of long pastern; _i_, synovial distension of the fetlock-joint; 7, suspensory ligament; 9, cannon bone; 10, outer sesamoid bone; 12, fetlock-joint; 13, lateral cartilage; 14, suspensory ligament of the lateral cartilage. (Ellenberger in Leisering’s Atlas and Veterinary Anatomy, Sisson, Saunders.)] [Illustration: FIG. 18. Right forefoot seen from the inner side; _d_, _d′_, _d″_, _d‴_, great sesamoid sheath; _e_, mucous bursa beneath anterior extensor tendon of the toe; _f_, synovial distension of fetlock-joint; 10, inner sesamoid bone; 11, “x” ligament; 14, fetlock-joint; 15, lateral cartilage; 16, suspensory ligament of lateral cartilage (Ellenberger in Leisering’s Atlas and Veterinary Anatomy, Sisson, Saunders.)] Altering the Relative Tension of the Flexor Tendons and Suspensory Ligament of the Fetlock-Joint. The body-weight imposed at the fetlock-joint is supported, in large part, by the suspensory ligament; somewhat less weight is borne by the perforans tendon, and a still smaller amount by the perforatus. The coronary joint is supported chiefly by the perforatus, assisted by the perforans. The pedal joint is pressed forward and upward by the perforans tendon passing in a curve beneath the navicular bone. Each of these three structures bears its normal proportion of the body-weight when the three phalanges, as viewed from the side, form a continuous straight line from the fetlock-joint to the ground. In such a case the obliquity of the long pastern will be the same as that of the toe (see Foot-Axis, p. 70). [Illustration: FIG. 19. Right forefoot viewed from the external side: _A_, os coronæ; _B_, os pedis; _C_, external lateral cartilage; _a_, lateral pedal ligament; _b_, ligament uniting the lateral cartilage with the os coronæ; _c_, aponeurosis joining lateral cartilage and os pedis.]