_+Musculus flexor hallucis brevis+_ (Fig. 4).--This minute muscle has a fleshy origin from the medial surface of the hypotarsus. The short belly terminates in a weak, slender tendon which passes down the posteromedial surface of the tarsometatarsus and into the space between the first metatarsal and the trochlea for digit II. In this region the tendon envelops the tendon of the _m. flexor hallucis longus_ and inserts on the distal end of the first metatarsal and on the proximal end of the first phalanx of the first digit. Action.--Flexes hallux; action must be slight. Comparison.--The small size of this muscle makes it exceedingly difficult to study. The muscle is larger in _Vireo_ than in any of the other species examined. This may be correlated with the smaller size of the _m. flexor hallucis longus_ in this species. The muscle does not seem to be so well developed in the cardueline finches as it is in the other species. _+Musculus abductor digiti IV+_ (Fig. 2).--Extremely small, delicate and difficult to demonstrate, this muscle arises in a fleshy origin immediately from underneath the posterior edge of the external cotyla of the tarsometatarsus. The tendon of insertion is long and slender and inserts along the lateral edge of the first phalanx of digit IV. Action.--Abducts digit IV. Comparison.--No significant differences noted among the species studied. _+Musculus lumbricalis.+_--Semitendinous throughout its length, this muscle arises from the ossified tendon of the _m. flexor digitorum longus_ at a point immediately proximal to the branching of this tendon. The insertion is on the joint pulleys and capsules at the base of the third and fourth digits. Action.--Hudson (1937:57) states that: "Meckel (_vide_ Gadow--1891, p. 204) considered this muscle as serving to draw the joint pulley behind in order to protect it from pinching during the bending of the toes. It perhaps also tends to flex the third and fourth digits." Comparison.--No significant differences noted among the species studied. Discussion of the Myological Investigations Simpson (1944:12) and others have emphasized that different parts of organisms evolve at different rates. Beecher (1951b:275) in stating that "... the hind limb is very similar in muscle pattern throughout the Order Passeriformes and seems to have become relatively static after attaining a high level of general efficiency ..." implies that the muscle pattern of the leg must be one of long standing and slow change. This concept was emphasized by Hudson (1937) who found but little variation in muscle pattern among members of the several families of passerine birds. The concept is further confirmed by the present investigation. The intricate patterns of origin and of insertion seem to remain almost the same throughout the order in spite of adaptive radiation which has occurred.