MUSCLES OF THE PELVIC LIMBS. 191 



dsity. 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, r). Medial surface with the ischium. Caudal border with 

 the quadratus femoris (Fig. 90, /). Cranial border with the 

 gemellus superior. 



Action. — Abductor of the thigh. The muscle may be con- 

 sidered as a separate head of the obturator internus (Fig. 

 90, e). 



M. quadratus femoris (Fig. 90,/). — 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 (r) beneath the proximal end of the biceps 

 femoris (Fig. 68, /). 



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, /), the semitendinosus (Fig. 90, _/'), and 

 the great sciatic nerve (Fig. 163, a'). Caudal border with the 

 semimembranosus (Fig. 90, /). Ventral border with the 

 adductor femoris (Fig. 90, //) ; 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^. 



Origin by fleshy fibres from the median lip of the obturator 

 foramen and from both dorsal and ventral surfaces of the rami 

 of the pubis and ischium adjacent to the lip. Also from the 



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