_Origin._—By a tendinous fascia from the post-acetabular ridge, extending between the antitrochanter and the anterior point of the insertion of the semitendinosus. _Insertion._—To the tuberosity on the external part of the shaft of the fibula a short distance below the head. _Shape._—Large, rather cone-shaped with base directed upward. _Relations._—Anteriorly, with the vastus externus; posteriorly, with the semitendinosus. The inferior tendinous portion passes through a tendinous sling or pulley called the biceps band. _Action._—Flexes the leg upon the thigh. =Semitendinosus= (Fig. 23, No. 10). _Location._—Posterior femoral region. _Origin._—By a tough, strong fascia from the surface of the caudal muscles and from the posterior third of the post-acetabular ridge. _Insertion._—The fibers pass downward and forward, and insert to the tendinous raphe along the posterior margin of the semitendinosus accessorius; lower down it merges with the median fascia of the inner head of the gastrocnemius. _Shape._—Fleshy, broad, flat and long. _Relations._—Internally, with the semimembranosus and anteriorly, with the biceps flexor cruris. _Action._—Flexes the leg. =Semitendinosus Accessorius.= _Location._—Posterior femoral region. _Origin._—From an oblique line just above the condyle, on the posterior of the shaft of the femur. _Insertion._—Its fibers, passing upward and backward, attach themselves to the tendinous raphe common to this muscle and the semitendinosus, and are finally inserted to the inner side of the shaft of the tibia. _Shape._—Flat, oblong. _Relations._—Posteriorly to the shaft of the femur, and externally to the long adductors of the thigh. _Action._—Aids the preceding in flexing the leg. =Semimembranosus= (Fig. 24, No. 17). _Location._—Postero-internal to the semitendinosus. _Origin._—From the outer surface of the ischium, beginning at the lower margin of its notch on the posterior pelvic border, extends on a curved line on the adjacent surface beyond. _Insertion._—The fibers, passing downward and forward, insert by a broad, thin tendon to the shaft of the tibia a short distance below the head and on a line parallel to the long axis of the tibia. _Shape._—Long, narrow, ribbon-shaped. _Relations._—Lies adjacent to the semitendinosus and in the same plane. _Action._—Directly flexes the leg. =Femoro-caudal= (Fig. 24, No. 8). _Location._—Infero-lateral to the caudal and post-femoral region. _Origin._—By a delicate tendon from the base of the pygostyle. _Insertion._—By a thin, flat tendon upon the outer part of the shaft of the femur below the trochanter and at about the juncture of the upper and middle third of the bone. [Illustration: