3G2 THE MUSCLES 



Variations. — The posterior part of the imi.sele may ftirm a distinct slip. Accessory bundles 

 from the semi-membranosus or biceps may join tlie lower tendon. The upper border of the 

 muscle may be blended with the quadratus femoris. 



4. GRACILIS 



The gracilis — named from its form ((//•aciV/s = slender) — is long and ribbon- 

 shaped. 



Origin. — The inner edge of the anterior surface of the body and descending 

 ramus of the os pul;)is from about the middle of the symphysis to the junction of 

 the rami of the pubes and ischium. 



Insertion. — The inner surface of the tibia below its inner tuberosity, behind 

 the inscrtii)n of the sartorius. 



Structure. — Arising by a broad and thin aponeurosis, the muscular fibres pass 

 down the inner surface of the thigh almost parallel to one another, but Avith a 

 slight convergence, so that the muscle in descending increases in thickness as it 

 diminishes in breadth. About two inches (5 cm.) above the inner condyle it 

 becomes a rounded flattened tendon. This runs behind the inner condyle, and, 

 after forming one of the two hamstring tendons which can be easily felt at the inner 

 border of the popliteal space, it passes forwards to be inserted in a slightly ex- 

 panded form below the inner tuberosity. A few fibres pass from its lower border 

 to the deep fascia of the leg. 



Nerve-supply. — From the third and fourth nerves of the lumbar plexus by a 

 branch from the superficial division of the obturator nerve which enters the deep 

 surface of the muscle above its middle. 



Action. — To adduct the thigh and flex the knee. "When the knee is flexed, it 

 will hel}) in rotating the leg inwards. 



Relations. — It lies superficially in its whole course under cover of the fascia 

 lata. Upon its deep surface lie the adductor brevis and magnus, and lower down 

 the semi-membranosus muscle. It has in front of it the sartorius muscle which 

 overlaps it slightly at the lower part of the thigh, and l^ehind it is the tendon of the 

 semi-tendinosus. The internal lateral ligament of the knee and a large bursa lie 

 beneath its tendon. 



5. OBTURATOR EXTERNUS 



The obturator externus (figs. 286, 289, and 290) — named from its attachment 

 to the oi)turator membrane upon its outer surface — is a triangular sheet. 



Origin. — (1) The inner half of the anterior surface of the obturator membrane; 

 (2) tlie descending ramus of the os pubis immediately internal to the foramen; (3) 

 the ascending ramus of the ischium internal to the foramen. 



Insertion. — The digital fossa upon the inner surface of the great trochanter. 



Structure. — It is a fan-shaped triangular muscle which arises fleshy from the 

 adjacent surfaces of bone and membrane, in a curve Avhich is convex forwards and 

 inwards. From this wide origin the fibres converge outwards, and end below the 

 acetabulum in a rounded tendon which passes behind and in close contact with the 

 capsule of the joint to its insertion in the digital fossa. Not unfrequently a small 

 portion of the muscle is scjiarated at its up})er 1)order from the rest by one or both 

 of the divisions of the oV)turator nerve. 



Nerve-supply. — From the third and fourth nerves of the lumbar plexus by 

 the deep division of the obturator nerve which distributes filaments to the deep 

 surface of the muscle as it is passing through it. 



Action. — To adduct and rotate outwards the thigh. 



Relations. — Behind, the obturator vessels, and at its insertion the quadratus 

 femoris; in front, the psoas muscle, the pectineus, and adductor Ijrevis; above, the 

 obturator nerve, one or both branches of which perforate it, and more externally 

 the capsule of the hip-joint. 



