GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on posterior aspect of shank deep to M. flexor perforatus digiti II and to proximal end of medial head of M. flexor perforatus digiti IV; bounded anterolaterally by M. flexor digitorum longus and anteromedially by M. plantaris; tendinous anteromedial surface of proximal end fused to common tendon of origin of medial heads of Mm. flexor perforatus digiti III and flexor perforatus digiti II; belly ending approximately halfway down shank. ORIGIN.--The origin is fleshy and tendinous (anteromedial surface) from the popliteal area immediately distal to the origin of the medial head of M. flexor perforatus digiti IV, extending laterally to the area immediately proximal to the external femoral condyle (medial to the origin of M. gastrocnemius pars externa); the muscle also arises from the proximal end of the posterior part of the articular capsule. INSERTION.--The slender ossified tendon becomes flexible and passes through the canal in the tibial cartilage that lies lateral to the canal for M. flexor perforatus digiti II, then passes through a slight groove in the lateral surface of the hypotarsus and becomes ossified again; midway of the tarsometatarsus, the tendon becomes superficial to the tendon of M. flexor digitorum longus and is connected with the latter by an extensive vinculum, which extends from the deep surface and lateral edge of the tendon of M. flexor hallucis longus distally to the superficial surface of the tendon of M. flexor digitorum longus; the tendon continues, unossified and considerably reduced in size, distally medial to the tendon of M. flexor digitorum longus, and passes through the flexor groove of the first metatarsal anterolateral (adjacent) to the tendon of M. flexor hallucis brevis, then passes deep to the terminal expansion of the latter onto the ventral surface of the hallux; the tendon emerges from under the end of the tendon of M. flexor hallucis brevis and attaches to the ventral surface of the ungual phalanx; a weak dorsal slip attaching to the ventral surface of the distal end of the first phalanx is usually present. INNERVATION.--A branch of the medial division of the tibial nerve passes along the medial edge of the muscle, giving several twigs into it. INDIVIDUAL VARIATION.--None of significance in any of the three species studied. =_M. Plantaris_=, Figs. 15, 19A _T. pallidicinctus_ GENERAL DESCRIPTION AND RELATIONS.--Elongate and tapering; on posteromedial surface of tibiotarsus; bounded medially by M. gastrocnemius pars interna and tendon of M. flexor cruris medialis, posteriorly by M. gastrocnemius pars media and medial head of M. flexor perforatus digiti III, posterolaterally by M. flexor hallucis longus; medial to M. flexor digitorum longus; anterolateral surface of proximal end often slightly overlapping and fused to posterior surface of medial end of M. popliteus; belly terminating above middle of shank.