_Origin_ from the ventral half of the crest of the ilium and from the medial half of its ventral border craniad of the auricular impression. The caudal third of the origin is by a thin tendon, the rest by fleshy fibres.
_Insertion_ on a long S-shaped line which begins on the dorsal border of the tibial shaft about two centimeters from its proximal end, passes thence to the middle of the proximal end of the medial surface of the tibia, thence across the ligaments of the knee-joint and the medial surface of the medial epicondyle to the patella, crosses the patella obliquely to the middle of its proximal end, and may be continued for some distance proximad along the middle line on the fascia.
_Relations._--Medial surface with the integument and proximad with the internal oblique muscle (Fig. 68, _p_). Lateral (inner) surface with the tensor fasciæ latæ (Fig. 68, _r_), the vastus lateralis (Fig. 90, _d_), the superficial fascia, the vastus medialis (Fig. 92, _c_), the rectus femoris (Fig. 92, _b_), and the distal end of the semimembranosus (Fig. 92, _h′_).
_Action._--Adducts and rotates the femur and extends the tibia.
=M. gracilis= (Fig. 91, _b_).--The gracilis is a flat, thin, subcutaneous muscle occupying the ventral half of the medial surface of the thigh.
_Origin_ by a strong tendon from the caudal three-fourths of the symphysis of the ischium and pubis. The tendon may extend caudad of the symphysis in the middle line to the level of the tuberosity of the ischium. For about its first centimeter the tendon is common to the two muscles of opposite sides and gives origin on two sides to the fibres of the adductor femoris. The common tendon divides into two which pass laterad, each ending in a convex border from which the muscle-fibres spring.
_Insertion._--It ends in a thin aponeurosis, part of which is continuous with that of the sartorius. The aponeurosis is finally inserted into the medial surface of the tibia near its proximal end, while distally it is continuous with the fascia.
_Relations._--Outer (medial) surface with the integument. Inner (lateral) surface with the semimembranosus (Fig. 91, _i_) and the adductor femoris (Fig. 91, _h_).
_Action._--Adducts the leg and draws it caudad.