=M. biceps femoris= (Fig. 68, _t_, page 117).--A very large flat muscle covering about two-thirds of the lateral side of the thigh.
_Origin_ (Fig. 90, 2).--From the ventral surface of the tuberosity of the ischium by tendon- and muscle-fibres. The fibres diverge, and near the knee the mass has spread out, ending in a fascia. The dorsal border of the muscle and the common fascia are continuous dorsad with the superficial fascia of the thigh and with the tendon of the caudofemoralis (Fig. 68, _s_). Ventrad it is continuous with the superficial fascia of the shank.
_Insertion_ into rather more than the proximal one-third of the dorsal border of the tibia along its lateral margin and into the lateral margin of the patella. In passing over the knee-joint it is closely united to the underlying ligaments and tendons.
_Relations._--Outer surface with the superficial fascia and with a few of the most caudal fibres of the cutaneus maximus (Fig. 62, _b_, page 94). Cranial (or dorsal) edge with the caudofemoralis (Fig. 68, _s_) and the vastus lateralis (Fig. 90, _d_). Caudal border with the semitendinosus (Fig. 68, _u_) and a mass of fat. Inner surface with the caudofemoralis (Fig. 68, _s_), the tenuissimus (Fig. 90, _g_), the obturator internus (Fig. 90, _e_), the quadratus femoris (Fig. 90, _f_), the semitendinosus (Fig. 68, _u_), the semimembranosus (Fig. 90, _i_), the adductor femoris (Fig. 90, _h_), the great sciatic nerve (Fig. 163, _a_), and distad with the following muscles of the lower leg: the tibialis anterior (Fig. 90, _n_), the extensor longus digitorum (Fig. 90, _p_), the peroneus longus (Fig. 90, _q_), and the lateral head of the gastrocnemius (Fig. 90, _m_).
_Action._--Abductor of the thigh, and flexor of the shank.
=M. tenuissimus= or =M. abductor cruris= (Fig. 90, _g_).--A very slender muscle, only three or four millimeters wide.
_Origin_ from the tip of the transverse process of the second caudal vertebra, in common with the caudofemoralis (Fig. 68, _s_) or gluteus maximus. It passes obliquely beneath the biceps femoris (Fig. 68, _t_) distad and ventrad, to the distal end of the ventral border of that muscle. Here it becomes continuous with the ventral border of the biceps, ending in a continuation of the same fascia into which the biceps is inserted.