_Insertion_ by fleshy fibres for about one centimeter in the middle line on the dorsal surface of the femur distad of the great trochanter. _Relations._--Outer surface with the gluteus minimus (Fig. 163, 5), the gemellus superior (6), and the vastus lateralis (Fig. 90, _d_). Inner surface with the ilium, the rectus femoris (Fig. 92, _b_), the capsule of the joint, and the vastus medialis (Fig. 92, _c_). _Action._--Rotates the thigh so as to carry the foot inward, hence antagonizes the iliopsoas. =M. gemellus inferior.=--The gemellus inferior is a flat triangular muscle situated just caudad of the gemellus superior and beneath the obturator internus (Fig. 90, _e_), so that it is seen on reflecting the latter _Origin_ from the dorsal one-half of the whole lateral surface of the ischium between the ischial spine and the ischial tuberosity. The fibres converge toward its insertion. The inner surface of the muscle is covered by a strong tendon. _Insertion_ into the inner surface of the tendon of the obturator internus (Fig. 90, _e_) by tendon- and muscle-fibres. Some of the muscle-fibres are inserted into the capsule of the joint. _Relations._--Outer surface with the obturator internus (Fig. 90, _e_). Medial surface with the ischium. Caudal border with the quadratus femoris (Fig. 90, _f_). Cranial border with the gemellus superior. _Action._--Abductor of the thigh. The muscle may be considered as a separate head of the obturator internus (Fig. 90, _e_). =M. quadratus femoris= (Fig. 90, _f_).--The quadratus femoris is a short thick muscle connecting the ischial tuberosity (2) and the proximal end of the femur. It lies just caudad of the obturator internus (_e_) beneath the proximal end of the biceps femoris (Fig. 68, _t_). The _origin_ is by fleshy fibres from a considerable triangular area on the lateral surface of the ischium near the tuberosity. The area lies between the origin areas of the gemellus inferior, biceps, semimembranosus, and the obturator externus. _Insertion_ into the distal two-thirds of the ventral border of the great trochanter and about half the adjacent surface of the lesser trochanter. _Relations._--Outer surface with the tenuissimus (Fig. 90, _g_), the biceps (Fig. 68, _t_), the semitendinosus (Fig. 90, _j_), and the great sciatic nerve (Fig. 163, _a_). Caudal border with the semimembranosus (Fig. 90, _i_). Ventral border with the adductor femoris (Fig. 90, _h_); dorsal border with the obturator internus (Fig. 90, _e_) and gemellus inferior. _Action._--Extensor of the thigh and rotator of the femur so as to carry the foot inward. =M. obturator externus.=--The obturator externus is a flat triangular muscle beneath the adductor femoris (Fig. 92, _g_).