3. The _lateral ligaments_ of the lateral _cartilages_, _navicular bone_, and _os pedis_. They are short, and unite the navicular bone with the os pedis and lateral cartilages. Of the three phalangeal articulations, the pedal is the only one that permits of any lateral movement; hence it is an imperfect hinge-joint. C. The Locomotory Organs of the Foot. Though the muscles are the organs which produce motion, the horseshoer need concern himself only with the tendons of those muscles which extend and flex the phalanges. These tendons are either =extensors= or =flexors=. The extensors lie on the _anterior face_ and the flexors on the _posterior face_ of the phalanges. [Illustration: FIG. 14. Right forefoot viewed from in front and from the external side: _a_, anterior extensor tendon of the toe; _b_, suspensory ligament of the fetlock; _b′_, branch of the same passing forward and uniting with the extensor tendon of the toe; _c_, extensor tendon of the os suffraginis (absent in the hind leg), called the lateral extensor.] The _anterior extensor of the phalanges_ (Fig. 14, _a_) extends the long and short pasterns and the hoof-bone; it is broad, and made somewhat broader by receiving the branches of the suspensory ligament (_b′_) that come from the sesamoid bones. It takes a firm attachment on the pyramidal eminence of the os pedis. In the forefeet the long pastern has a special extensor tendon (_c_), which is known as the _lateral extensor_. When the muscles to which these tendons are attached act,—that is, when they draw themselves together, or _contract_, as we term this action,—the foot is carried forward (extended). There are _two flexor tendons_ of the phalanges,—namely, the _superficial_ (perforatus tendon) and the _deep_ (perforans tendon). [Illustration: FIG. 15. Right forefoot seen from behind: _a_, lower end of the perforans tendon, cut through and hanging down, so that its anterior surface is visible; _a′_, lower expanded end (plantar aponeurosis) of this tendon, which attaches itself to the semilunar crest of the os pedis; _a″_, shallow groove which receives the slight elevation on the under surface of the navicular bone; _a‴_, piece of the perforans tendon enclosed by the ring formed by the perforatus tendon; _b_, perforatus tendon bent over backward so that its anterior surface is visible; _b′_, ring of the perforatus tendon; _b″_, terminal branches of the same; the perforans tendon passes through the space between these two branches; _c_, navicular bone; _d_, suspensory ligament of the same; _e_, smooth surface on the os coronæ over which the perforans tendon glides; _f_, the smooth groove (sesamoid groove) on the posterior surface of the intersesamoid ligament for the gliding of the perforans tendon; _g_, body of the suspensory ligament of the fetlock; _g′_, terminal branches of the same, attaching to the sesamoid bones.]