_Shape._—Small flat muscle. _Relations._—Posteriorly with the metatarsus. _Action._—Extensor of the fourth toe. =Tibialis Posticus= (Fig. 24, No. 23). _Location._—In the posterior tibial region. _Origin._—From the whole shaft of the fibula below the insertion of the biceps flexor cruris, and from the shaft of the tibia a short distance below this insertion. Also from the interosseous membrane, and the adjacent surface of the tibial shaft. _Insertion._—Passing in front of the external malleolus, crossing the ankle-joint, finally inserted into the outer edge of the summit of the tarso-metatarsal bone. _Shape._—Long, subcylindrical. _Relations._—Medially, with the flexor perforans digitorum pedis; superiorly, with the postero-external portion of the tibia. _Action._—Extends the metatarsus upon the tibia. =Flexor Perforatus Indicis Secundus Pedis= (Fig. 17, No. 5). _Location._—The posterior tibial region. _Origin._—From the external surface of the outer condyle of the femur, just below the head of the gastrocnemius. _Insertion._—Passing in an oblique manner along posterior to the tibia, extends through the superficial part of the tibial cartilage to the outer side of the leg; then crossing the tibio-tarsal joint, it passes through a special canal of the hypotarsus, down the back of the tarso-metatarsus, under the annular ligament of the sole of the foot and a cartilaginous structure below this ligament, over the trochlea, and is inserted to the middle shaft of the second phalanx of the second toe. _Shape._—Thin, flat, broadly spindle-shaped. _Relations._—Posteriorly, with the flexor perforatus medius secundus pedis, and anteriorly, with the flexor perforatus annularis primus pedis. _Action._—Flexes the toes. =Flexor Longus Hallucis= (Fig. 17, No. 7; Fig. 25, No. 2). _Location._—The posterior tibial region. _Origin._—By two tendinous heads: one from the posterior part of the femur, just below the two condyles; the other from the outer part of the external condyle of the femur. The deep flexor passes between these two heads. _Insertion._—Becoming tendinous at the lower third of the leg, passes beneath the superficial flexors in a special canal on the outer side of the tibial cartilage, and extends through the large canal of the hypotarsus (Fig. 12, No. _F_, 5) next to the shaft, then down to the apex of the accessory metacarpal bone. It is inserted to the tubercle on the inferior proximal end of the ungual phalanx. _Shape._—Large, fusiform. _Relations._—With the exterior of the deep flexors. _Action._—Flexes the hallux as its long flexor. =Flexor Perforatus Annularis Primus Pedis= (Fig. 17, Nos. _D_, 8 and _C_, 6). _Location._—The posterior tibial region. _Origin._—From the inner side of the belly of the flexor longus hallucis.