188 THE MUSCLES. 
Lusertion 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 caude 
internus, the tenuissimus (Fig. 90, g), the great sciatic nerve 
(Fig. 163, a), the obturator internus (Fig. 90, e), the gluteus 
medius (Fig. 90, 4), the gemellus superior, and the pyriformis 
(Fig. 163, 7). Cranial border with the gluteus medius and 
the tensor fasciz late. Caudal border with the caudofemoralis 
(Fig. 68, s). 
Action. —Abducts the thigh. 
M. gluteus medius (Fig. 90, 4).—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 sur- 
face of the supraspinous extensor muscles of the tail; (3) from 
the fascia intervening between it and the tensor fascie# late; 
(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 
vertebrz. The fibres converge to. a strong internal tendon. 
Insertion into the proximal end of the great trochanter. 
Welations.—Outer surface with the gluteus maximus and 
tensor fasciz lata, 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 fasciz late. Caudal 
border with the gluteus maximus. 
Action.—Abducts the thigh. 
M. pyriformis (Fig. 163, 7).—The pyriformis is a triangu- 
lar muscle covered by the gluteus maximus and the gluteus 
medius (Fig. 90, 4) and overlying the gemellus superior (ig. 
163, 6). 
