_+Musculus iliotibialis+_ (Fig. 1).--Broad and triangular, this muscle covers most of the deeper muscles of the lateral aspect of the thigh. The middle region is fused with the underlying _femorotibialis_ muscles. In the distal half of this muscle there are three distinct parts; the anterior and posterior edges are fleshy and the central part is aponeurotic. The origin is from a narrow line along the iliac crests--from the origin of the _m. sartorius_, anteriorly, to the origin of the _m. semitendinosus_ posteriorly. The origin is aponeurotic in the preacetabular region but fleshy in the postacetabular region. The distal part of the muscle is aponeurotic and joins with the _femorotibialis_ muscles in the formation of the patellar tendon. This tendon incloses the patella and inserts on a line along the proximal edges of the cnemial crests of the tibiotarsus. Action.--Extends crus. Comparison.--In _Vireo_ the central aponeurotic portion of this muscle is absent. _+Musculus femorotibialis externus+_ (Fig. 2).--Covering the lateral and anterolateral surfaces of the femur, this large muscle has a fleshy origin from the lateral edge of the proximal three-fourths of the femur. The origin separates the insertion of the _m. iliotrochantericus anticus_ from that of the _m. ischiofemoralis_ and, in turn, is separated from the origin of the _m. femorotibialis medius_ by the insertions of the _m. iliotrochantericus anticus_ and _m. iliotrochantericus medius_. Approximately midway of the length of the femur this muscle fuses anteromesially with the _m. femorotibialis medius_. Distally, the _m. femorotibialis externus_ contributes to the formation of the patellar tendon which inserts on a line along the proximal edges of the cnemial crests of the tibiotarsus. Action.--Extends crus. Comparison.--No significant differences noted among the species studied. _+Musculus femorotibialis medius+_ (Figs. 2, 4).--The origin of this muscle, which lies along the anterior edge of the femur, is fleshy from the entire length of the femur proximal to the level of attachment of the proximal arm of the biceps loop. Laterally this muscle is completely fused for most of its length with the _m. femorotibialis externus_ and contributes to the formation of the patellar tendon, which inserts on a line along the proximal edges of the cnemial crests of the tibiotarsus. Many of the fibers, nevertheless, insert on the proximal edge of the patella. Action.--Extends crus. Comparison.--No significant differences noted among the species studied.