Comparison.--No significant differences noted among the species studied.
_+Musculus flexor perforans et perforatus digiti II+_ (Figs. 2, 9).--Small and spindle-shaped, this muscle lies on the posterolateral side of the crus immediately beneath the _pars externa_ of the _m. gastrocnemius_. The origin is fleshy and arises in company with the _m. flexor perforans et perforatus digiti III_ from a point on the posterolateral surface of the distal end of the femur between the point of origin of the _pars externa_ of the _m. gastrocnemius_ and the fibular condyle. The belly extends approximately one-fourth of the way down the crus and gives rise to the tendon of insertion which passes distally and superficially through the posterior edge of the tibial cartilage. The tendon traverses the posteromedial canal of the hypotarsus (Fig. 6) and continues along the posterior surface of the tarsometatarsus. Between the first metatarsal and the base of the second digit the tendon is enclosed by the medial surface of a sesamoid bone. This tendon then perforates that of the _m. flexor perforatus digiti II_ at the level of the first phalanx and in turn is perforated by the tendon of the _m. flexor digitorum longus_ at the proximal end of the second phalanx. The insertion is on the posterior surface of the second phalanx.
Comparison.--In _Passer_, _Estrilda_, _Poephila_, _Hesperiphona_, _Carpodacus_, _Pinicola_, _Leucosticte_, _Spinus_, and _Loxia_ the proximal portion of this muscle is more intimately connected with the posterior edge of the _m. flexor perforans et perforatus digiti III_ than it is in the other species examined.
_+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.