THE INTERNAL MUSCLES OF THE THIGH 283 



thus divided into two brandies. The outer branch is inserted into the back of the 

 femur witli the short portion, while the inner branch is attached to the internal 

 epicondyle and lateral ligament. There is often a superficial slip which reaches 

 the internal straight patellar ligament. Some fibers pass under the lateral ligament 

 and end on the tendon of the semimembranosus. 



Relations. — Internally, the gracilis, and branches of the femoral artery and of 

 the obturator nerve; externally, the femur, the obturator externus, quadratus 

 femoris, biceps femoris, and gastrocnemius, and the femoral, deep femoral, and 

 obturator arteries; anteriorly, the pectineus, vastus internus, and a large branch 

 of the obturator nerve; posteriorly, the semimembranosus and the great sciatic 

 nerve. 



Blood-supply. — Femoral, deep femoral, and obturator arteries. 



Nerve-supply. — Obturator nerve. 



3. Semimembranosus.— Described on p. 280. 



Third Layer 



1. Quadratus femoris (Ischio-femoralis). — This is a narrow, flat muscle, 

 which lies under cover of the upper part of the adductor (Figs. 455, 456). 



Origin. — -The ventral surface of the ischium, just in front of the semimembrano- 

 sus. 



Insertion. — An oblique line on the posterior surface of the femur, near the 

 lower part of the internal trochanter. 



Action. — To extend the hip joint, and to adduct the thigh and rotate it out- 

 ward. 



Structure. — It is composed of parallel bundles of fibers directed downward, 

 forward, and outward. 



Relations. — ^Internally, the adductor, semimembranosus, and the obturator 

 vessels; externally, the obturator externus and biceps femoris, the deep femoral 

 artery, and the great sciatic nerve. 



Blood-supply. — Deep femoral and obturator arteries. 



Nerve-supply .^-Greai sciatic nerve. 



2. Obturator Externus (Fig. 456) . — This is a pyramidal muscle which extends 

 across the back of the hip joint from the ol^turator foramen to the trochanteric 

 fossa. 



Origin. — The ventral surface of the j^ubis and ischium, and the margin of the 

 obturator foramen. 



Insertion. — The trochanteric fossa. 



Action. — -To adduct the thigh and to rotate it outward. 



Structure.— It is almost entirely fleshy, the muscle-bundles being rather loosely 

 connected. The insertion is pointed, flattened, and partly tendinous. The origin 

 is perforated by the obturator vessels and nerve. 



Relations. — -Internally, the adductor and quadratus femoris and the deep 

 femoral vessels; externally, the gemellus, the tendon of the obturator internus, the 

 biceps femoris, and the great sciatic nerve; anteriorly, the hip joint, the pectineus, 

 and the external pudic vein. 



Blood-supply. — -Deep femoral and obturator arteries. 



Nerve-supply. — ^Obturator nerve. 



3. Obturator internus (Fig. 451). — This arises by two heads within the pelvic 

 cavity, the tendon emerging through the lesser sciatic foramen. 



Origin. — (1) The pelvic surface of the pubis and ischium around the obturator 

 foramen; (2) the pelvic surface of the shaft of the ilium and the wing of the sacrum. 

 Insertion. — The trochanteric fossa. 

 Action. — To rotate the femur outward. 



