_+Musculus flexor perforatus digiti III+_ (Fig. 5).--Long and flattened, this muscle lies on the posteromedial side of the crus beneath the _m. gastrocnemius_. The belly is tightly fused laterally with the belly of the _m. flexor hallucis longus_ and posteriorly with the belly of the _m. flexor perforatus digiti IV_. The origin is by a long, strong tendon from a small tubercle just medial to, and at the proximal end of, the external condyle of the femur. Below the middle of the crus this muscle terminates in a strong tendon which perforates the tibial cartilage near its lateral edge. In this region the tendon is sheathlike and wrapped around the tendon of the _m. flexor perforatus digiti IV_. These two tendons together pass through the posterolateral canal of the hypotarsus (Fig. 6). Immediately distal to the hypotarsus the two tendons separate, and the tendon of the _m. flexor perforatus digiti III_ receives a branch of the tendon of the _m. peroneus longus_. The tendon passes distally over the surface of the second trochlea, and its insertion is sheathlike on the posterior surface of the first phalanx, and on the proximal end of the second. In the area of insertion this tendon is perforated by that of the _m. flexor perforans et perforatus digiti III_ and by that of the _m. flexor digitorum longus_ to the third digit. Action.--Flexes digit III. Comparison.--In _Passer_, _Estrilda_, _Poephila_, _Hesperiphona_, _Carpodacus_, _Pinicola_, _Leucosticte_, _Spinus_, and _Loxia_ the edges of the sheathlike tendon are thickened at the points of insertion, so that the tendon appears to have two branches which insert along the posterolateral edges of the first phalanx and are connected medially by a fascia.