_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. _Relations_.--Outer surface with the caudofemoralis (Fig. 68, _s_) and the biceps femoris (Fig. 68, _t_); distad with the integument. Inner surface with the obturator internus (Fig. 90, _e_), quadratus femoris (_f_), semitendinosus (_j_), adductor femoris (_h_), semimembranosus (_i_), and distad with the muscles of the lower leg. =M. caudofemoralis= (=parameralis=, Strauss-Durckheim) (Fig. 68, _s_, page 117). _Origin_ by a flat tendon from the transverse processes of the second and third caudal vertebræ. The muscle forms a flat band which passes distad along the middle of the lateral side of the thigh over the pelvis and caudad of the great trochanter. At the middle of the thigh it ends in a very thin tendon. The tendon passes distad along the medial surface of the biceps femoris (Fig. 68, _t_), pierces the fascia lata near the knee, and passes to its _Insertion_ into the middle of the lateral border of the patella. _Relations._--Outer surface with the superficial fascia and a few fibres of the cutaneus maximus; distad with the biceps femoris (Fig. 68, _t_). Cranial border with the gluteus maximus; caudal border with the biceps femoris. Inner surface with the tenuissimus (Fig. 90, _g_), the gluteus maximus, the abductor caudæ internus, and with the obturator internus (Fig. 90, _e_); distad with the vastus lateralis. _Action._--Abducts the thigh and helps to extend the shank.