=M. semimembranosus= (Figs. 90 and 91, _i_; Fig. 92, _h_).--A thick prismatic muscle lying along the ventral (or caudal) side of the thigh between the semitendinosus (_j_) and the gracilis (Fig. 91, _b_).
_Origin_ by short tendon-fibres from the caudal border of the tuberosity and the ramus of the ischium. The muscle mass is divided throughout most of its length into two portions (Fig. 92, _h_ and _h′_), one of which (_h′_) lies laterad and caudad of the other. The two portions pass to the medial side of the knee. The caudal portion (_h′_) ends in a strong flat tendon five millimeters broad, the
_Insertion_ of which is into the medial surface of the femur on the medial epicondyle, at the middle of its distal border and into the adjacent medial surface of the tibia behind the lateral ligament.
The dorsal part has its _insertion_ into the distal one and one-half to two centimeters of the ridge which is continued from the medial epicondyle of the femur onto the shaft; and into the sesamoid bone of the medial epicondyle.
_Relations._--Lateral surface with the semitendinosus (Fig. 90, _j_), the biceps femoris (Fig. 68, _t_), and distad with a small part of the adductor femoris (Fig. 92, _g_), and with the gastrocnemius (Fig. 92, _j_). Medial surface with the gracilis (Fig. 91, _b_) and distad with the sartorius (Fig. 91, _a_). Cranial (or dorsal) border at the origin with the quadratus femoris (Fig. 90, _f_); for the remainder of its length with the adductor femoris (Fig. 90, _h_). Caudal border with the integument proximad.
[Illustration: FIG. 91.--MUSCLES ON THE MEDIAL SIDE OF THE LEG.
_a_, M. sartorius; _b_, M. gracilis; _c_, M. iliopsoas; _d_, M. rectus femoris; _e_, M. vastus medialis; _f_, M. pectineus; _g_, M. adductor longus; _h_, M. adductor femoris; _i_, M. semimembranosus; _j_, M. semitendinosus; _k_, medial head of M. gastrocnemius; _l_, M. plantaris; _m_, M. flexor longus hallucis (_m′_, its tendon); _n_, M. flexor longus digitorum; (_n′_, its tendon); _o_, M. tibialis posterior; _p_, M. tibialis anterior; _q_, M. interosseus of second digit. 1, patella; 2, calcaneus; 3, medial malleolus; 4, second metatarsal; 5, transverse ligament of the lower leg.]
=M. sartorius= (Fig. 91, _a_; Fig. 68, _q_).--A large flat muscle along the medial side of the thigh near its cranial (dorsal) border.