GENERAL DESCRIPTION AND RELATIONS.--Bipinnate; on posterior aspect of shank deep to M. flexor perforatus digiti IV and between two heads of M. flexor perforatus digiti III; bounded anteriorly by Mm. flexor digitorum longus and flexor hallucis longus; proximal part divided into three small heads--medial, lateral, and anterolateral; medial and proximal parts of _medial head_ tendinous and extremely thin except for ossified medial edge; proximal part of _lateral head_ tendinous and lateral to insertional tendon of M. extensor iliofibularis; both tendinous and fleshy parts fused to overlying tendon of M. flexor perforatus digiti IV; narrow _anterolateral head_ fused to overlying anterolateral head of latter muscle and (anterolateral edge) to ossified tendon of anterolateral head of M. flexor perforatus digiti III; lateral edge of common belly fused to latter head; medial edge of muscle fused to medial heads of Mm. flexor perforatus digiti IV and flexor perforatus digiti III and to M. flexor hallucis longus. ORIGIN.--The _medial head_ attaches by a slender ossified tendon to the medial part of the popliteal area in common with the medial head of M. flexor perforatus digiti III and with the medial edges of Mm. flexor perforatus digiti IV (medial head) and flexor hallucis longus; this head is also fused to the articular capsule. The above-mentioned ossified part of the tendon is situated at the junction of M. flexor perforatus digiti II and M. flexor perforatus digiti III (medial head) and could be considered to be a part of the latter rather than the former. The flat tendon of the _lateral head_ arises in common with the lateral head of M. flexor perforatus digiti IV (which see). The _anterolateral head_ arises in common with the anterolateral heads of Mm. flexor perforatus digiti IV and flexor perforatus digiti III (see former).