=Plantaris.=--In quadrupeds this muscle is blended with the superficial flexor of the toes, which we will study afterwards. =Popliteus= (Fig. 87, 16; Fig. 88, 14).--In man, this muscle, which occupies the posterior surface of the tibia, above the oblique line, is completely covered by the gastrocnemius. In quadrupeds, where it is more voluminous, it projects internally beyond the gastrocnemius, so that it is seen in the internal and superior part of the region of the superficial layer of muscles, immediately behind the internal surface of the tibia, which, as we know, is subcutaneous. The popliteus arises from the external surface of the external condyle of the femur. Thence its fibres which diverge pass to be inserted into the superior part of the posterior surface and of the internal border of the tibia. It is in this latter region that it projects beyond the gastrocnemius, but we may add that there it is more or less covered by the semi-tendinosus. It flexes the leg, and rotates it forwards. =Superficial Flexor of the Toes= (Fig. 83, 13, 15; Fig. 84, 17; Fig. 86, 11, 13, 13; Fig. 87, 17; Fig. 88, 15, 18, 18).--In man, the homologue of this muscle is found in the sole of the foot. It is called _the short flexor of the toes_. It arises from the calcaneum, and passes to the four outer toes. In quadrupeds, it rises as high as the back of the knee, and is found blended with the plantaris. Further designated by the name of _the superficial flexor of the phalanges_, covered in part by the gastrocnemius, with which it is in relation for a great part of the course which it traverses, this muscle arises from the posterior surface of the femur, on the external branch of the inferior bifurcation of the linea aspera. In the horse, this origin takes place in a depression situated above the external condyle, in the supracondyloid fossa. Then it accompanies the gastrocnemius, and becomes tendinous where the tendo-Achillis commences. It then winds round the latter in placing itself on its inner side, then on its posterior surface, and reaches the calcaneum. It accordingly contributes, as we have already pointed out, to form the cord of the ham. After having become expanded, and having covered as with a sort of fibrous cap the bone of the heel, it descends behind the metatarsus, and presents there an arrangement analogous to that which we pointed out in connection with the superficial flexor of the digits--that is, it contributes to form the _tendon_. This prominence, in the form of a cord, we see behind the canon-bone in solipeds and ruminants. It finally terminates in the same way as the muscle with which we have compared it (see p. 197).