_Origin_ (Fig. 163, 3, page 401) by fleshy fibres from the tips of the transverse processes of the last sacral and the first caudal vertebræ, from the fascia covering the spinous muscles dorsad of the transverse processes of these vertebræ, and from the fascia covering the gluteus medius. The muscle passes laterad and slightly caudad to its _Insertion_ by tendon and muscle-fibres into a tubercle on the caudal side of the great trochanter at the middle of its distal end, and for a few millimeters into the ridge which continues distad from this tubercle. _Relations._--Outer surface with the caudofemoralis (Fig. 68, _s_, page 117), the superficial fascia, and a few fibres of the cutaneus maximus. Inner surface with the abductor caudæ internus, the tenuissimus (Fig. 90, _g_), the great sciatic nerve (Fig. 163, _a_), the obturator internus (Fig. 90, _e_), the gluteus medius (Fig. 90, _b_), the gemellus superior, and the pyriformis (Fig. 163, 7). Cranial border with the gluteus medius and the tensor fasciæ latæ. Caudal border with the caudofemoralis (Fig. 68, _s_). _Action._--Abducts the thigh. =M. gluteus medius= (Fig. 90, _b_).--The gluteus medius is a very large triangular muscle which connects the ilium and the sacrum with the great trochanter (1). _Origin_ by fleshy fibres (1) from the superficial sacral fascia; (2) from the lateral surface of the fascia which covers the surface of the supraspinous extensor muscles of the tail; (3) from the fascia intervening between it and the tensor fasciæ latæ; (4) by tendon fibres from the dorsal half of the crest of the ilium and its dorsal border, and the dorsal half of the lateral surface craniad of the auricular impression; and (5) from the tips of the transverse processes of the last sacral and the first caudal vertebræ. The fibres converge to a strong internal tendon. _Insertion_ into the proximal end of the great trochanter. _Relations._--Outer surface with the gluteus maximus and tensor fasciæ latæ, and between these with the strong fascia lying beneath the cutaneus maximus muscle. Inner surface with the gluteus minimus, the pyriformis, and the gemellus superior. Cranial border with the tensor fasciæ latæ. Caudal border with the gluteus maximus. _Action._--Abducts the thigh. =M. pyriformis= (Fig. 163, 7).--The pyriformis is a triangular muscle covered by the gluteus maximus and the gluteus medius (Fig. 90, _b_) and overlying the gemellus superior (Fig. 163, 6). _Origin_ by fleshy fibres from the tips of the transverse processes of the last two sacral and the first caudal vertebræ. The muscle passes laterad through the great sciatic notch to its _Insertion_ by a flat tendon into an elongated area on the proximal border of the great trochanter just outside (caudad) of the insertion of the gemellus superior.