Human Anatomy - Kotsan I. Ya. 2009

Muscles and Fascia of the Lower Limb
Muscles of the Free Lower Limb
Posterior Thigh Muscles

The posterior group of thigh Muscles comprises three muscles: the biceps femoris, semitendinosus, and semimembranosus (Fig. 130). The primary function of the Posterior Muscle group is to extend the thigh at the hip joint and flex the leg at the knee joint.

The biceps femoris (m. biceps femoris) is located on the lateral side of the posterior surface of the thigh. As its name indicates, this muscle has two heads: long and short. The long HEAD (caput longum) originates together with the semitendinosus from the ischial tuberosity and the sacrotuberous ligament. At the level of the lower third of the thigh, the long head separates from the semitendinosus, joins the short head, and continues into a flat tendon. The short head (caput breve) originates from the lateral lip of the linea aspera, the lateral supracondylar line of the Femur, and the lateral intermuscular septum of the thigh. The common tendon of the muscle runs downwards along the posterolateral aspect of the knee joint and inserts into the head of the Fibula and the lateral surface of the lateral condyle of the Tibia (some tendon fibers continue into the Fascia of the leg). Located between the tendon of the biceps femoris and the fibular collateral ligament is the inferior subtendinous bursa of the biceps femoris (bursa subtendinea musculi bicipitis femoris inferior). Function: extends the thigh at the hip joint, flexes the leg at the knee joint, and rotates the flexed leg laterally.

Innervation: long head — tibial nerve (S_I–S_II), short head — common fibular nerve (L_IV–S_I).

The semitendinosus (m. semitendinosus) is named for its long tendon, which occupies nearly its entire distal half. The semitendinosus lies medially on the posterior surface of the thigh. It originates from the ischial tuberosity in common with the long head of the biceps femoris, runs downwards and slightly medially, and inserts onto the Medial surface of the tibial tuberosity. Some of the terminal tendon fibers blend into the fascia of the leg, contributing to The formation of the superficial pes anserinus. Function: extends and internally rotates the thigh, flexes and internally rotates the leg.

Innervation: tibial nerve (L_IV–S_II).

The semimembranosus (m. semimembranosus) is named for its broad, flat tendon, which forms almost the entire proximal half of the muscle. The semimembranosus lies deep to the semitendinosus. It originates from the ischial tuberosity of the hip bone. Near its insertion site, the terminal tendon divides into three slips that form the so-called deep pes anserinus. One slip attaches to the medial condyle of the tibia, the second to the fascia covering the popliteal muscle, and the third turns upward onto the posterior wall of the knee joint, continuing as the oblique popliteal ligament. At the point where the tendon divides into separate slips, the bursa of the semimembranosus (bursa m. semimemranosi) is formed. Function: extends and internally rotates the thigh, flexes and internally rotates the leg.

Innervation: tibial nerve (L_IV–L_V; S_I).