Action.—Moves thigh forward and upward and extends shank.
Comparison.—In Loxia and Spinus, only one-third of the origin is from the last free dorsal vertebra. In Hesperiphona, Carpodacus, Pinicola, and Leucosticte, only one-fifth of the origin is from this vertebra.
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.