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.
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.
Comparison.--No significant differences noted among the species studied.
_+Musculus femorotibialis internus+_ (Fig. 4).--One of the most superficial muscles lying on the medial surface of the thigh, this muscle is divided, especially near the distal end, into two parts, lateral and medial. The origin of the lateral part is fleshy from a line on the medial surface of the femur; the origin begins proximally at a point near the insertion of the _m. iliacus_. The medial, bulkier part of the muscle has a fleshy origin on the medial surface of the lower one-third of the femur. The two parts fuse to some extent above the points of insertion and insert on the medial edge of the head of the tibia.