The semitendinosus, remarkable for the great length of its
tendon of insertion, is situated at the posterior and medial aspect of the
thigh. It arises from the lower and medial impression on the upper part of the
tuberosity of the ischium, by a tendon common to it and the long head of the
biceps femoris; it also arises from an
aponeurosis which connects the adjacent surfaces of the two muscles to the extent of about 7.5 cm. from their origin. The muscle is
fusiform and ends a little below the middle of the thigh in a long round tendon which lies along the medial side of the
popliteal fossa; it then curves around the
medial condyle of the
tibia and passes over the
medial collateral ligament of the
knee-joint, from which it is separated by a
bursa, and is inserted into the upper part of the medial surface of the
body of the tibia, nearly as far forward as its anterior crest. The semitendinosus is more superficial than the semimembranosus (with which it shares very close insertion and attachment points). However, as the semimembranosus is wider and flatter than the semitendinosus, it is possible to palpate the semimembranosus directly. At its insertion it gives off from its lower border a prolongation to the
deep fascia of the leg and lies behind the tendon of the
sartorius, and below that of the
gracilis, to which it is united. These three tendons form what is known as the
pes anserinus, so named because it looks like the foot of a goose.
Innervation A
lower motor neuron exits to the
sacral plexus exiting through the spinal levels L5-S2. From the sacral plexus, the lower motor neuron travels down the
sciatic nerve. The sciatic nerve branches into the deep fibular nerve and the tibial nerve. The tibial nerve innervates the semitendinosus as well as the other hamstring muscles, the
semimembranosus and
biceps femoris. ==Function==