MUSCLES OF THE PELVIC LIMBS. I9t 
osity. 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, ¢) 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, ¢). Medial surface with the ischium. Caudal border with 
the quadratus femoris (Fig. 90, 7). 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. 
gO, ¢). 
M. quadratus femoris (Fig. 90, £).—The quadratus femoris 
isa short thick muscle connecting the ischial tuberosity (2) 
and the proximal end of the femur. It lies just caudad of the 
obturator internus (¢) beneath the proximal end of the biceps 
femoris (Fig. 68, 2). 
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, ¢), 
the biceps (Fig. 68, #), the semitendinosus (Fig. 90, 7), and 
the great sciatic nerve (Fig. 163, @). Caudal border with the 
semimembranosus (Fig. 90, 7). Ventral border with the 
adductor femoris (Fig. 90, 2); dorsal border with the obturator 
internus (Fig. 90, ¢) 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 
