_+Musculus flexor perforans et perforatus digiti III+_ (Fig. 2).--Long and pinnate, this muscle lies on the lateral surface of the crus beneath the _m. peroneus longus_ and _pars externa_ of the _m. gastrocnemius_. There are two distinct heads. The origin of the anterior head is fleshy from the proximal edge of the outer cnemial crest and from the internal edge of the distal end of the patellar tendon. The posterior head arises by a tendon from the femur in company with the _m. flexor perforans et perforatus digiti II_, is connected also with the tendon of origin of the _m. flexor perforatus digiti II_, and is loosely attached to the head of the fibula. Fibers from the belly of the muscle attach throughout its length to the lateral edge of the fibula, and the muscle is tightly fused also with adjacent muscles. The tendon of insertion is formed approximately one-half the way down the crus. The tendon perforates the posterior surface of the tibial cartilage and passes through the posteromedial canal of the hypotarsus (Fig. 6). At the base of the third digit the tendon ensheathes that of the _m. flexor digitorum longus_ and the two together perforate the tendon of the _m. flexor perforatus digiti III_. Immediately distal to this perforation the tendon of the _m. flexor perforans et perforatus digiti III_ ceases to ensheath that of the _m. flexor digitorum longus_. The latter passes beneath that of the former. Near the distal end of the second phalanx the tendon of the _m. flexor digitorum longus_ perforates that of the _m. flexor perforans et perforatus digiti III_. The latter inserts on the posterior surface of the distal end of the second phalanx and the proximal end of the third. Action.--Flexes digit III. Comparison.--In _Passer_, _Estrilda_, and _Poephila_, and in all the cardueline finches examined the proximal portion of this muscle is more intimately connected with the anterior edge of the _m. flexor perforans et perforatus digiti II_ than it is in the other species examined.