The =two lateral cartilages= (Figs. 19, _C_ and 20, _b_) are irregular, quadrangular plates, attached to the wings of the os pedis, and extending so far upward and backward that one can feel them yield to pressure on the skin above the coronet, and can thus test their elasticity. The perforans tendon and the plantar cushion lie between the lateral cartilages, and on the sides and behind are partially enclosed by them. The internal concave surface of the lateral cartilage (Fig. 20) is attached to the plantar cushion, the os pedis, and the navicular bone, and, like the external, slightly convex surface, is covered with many blood-vessels (veins) Fig. 25, _B_. [Illustration: FIG. 23. Section lengthwise through middle of the plantar cushion: _a_, glome (bulb) of heels; _b_, apex or point of fleshy frog; _c_, fibro fatty tissue of plantar cushion; _d_, median cleft which receives the frog-stay of the horny frog.] The =plantar cushion= (Figs. 21, 22, 23) is composed almost entirely of yellow elastic and white fibrous tissues, with adipose (fat) cells distributed throughout their substance. It is similar in form to the horny frog, and lies between it and the perforans tendon (Fig. 24, _a_). The bulbs are formed by the posterior thicker portion which lies between the lateral cartilages and is divided into two parts by the cleft or median lacuna (Figs. 21, _a_, and 23, _d_). The summit is attached to the plantar face of the os pedis in front of the semilunar crest, and the bulbs are attached to the lateral cartilages. It is covered inferiorly by the velvety tissue of the frog (pododerm). [Illustration: FIG. 24. Right forefoot viewed from below, behind, and the external side. This figure shows clearly the position of the plantar cushion. The external lateral cartilage and the tissues covering the plantar cushion and under surface of the os pedis (velvety tissue of the sole and fleshy frog) have been removed: _a_, fleshy frog or plantar cushion; _a′_, bulbs of plantar cushion; the remaining visible parts belong to the so-called “fleshy frog;” _a″_, groove (median lacuna) in the lower surface of the fleshy frog, in which lies the frog-stay of the horny frog; _b_, suspensory ligament of the plantar cushion passing out of the bulbs; _b′_, small elastic cords passing to the lateral cartilage; _c_, elastic ligament coming from the lateral cartilage and uniting with the suspensory ligament of the plantar cushion; _d_, small tendinous cord beginning in the skin behind the fetlock-joint and ending on the os suffraginis in common with _b_ and _c_; _e_, tendinous reinforcing sheath of the perforans tendon; _f_, reinforcing stay of the perforatus tendon; _g_, perforatus tendon; _h_, perforans tendon; _i_, suspensory ligament of the fetlock; _k_, plantar surface of the os pedis, to which the plantar cushion is joined by fibrous bands.] E. The Blood-Vessels and Nerves.