358 THE MUSCLES 



5. QUADRATUS FEMORIS 



The quadratus femoris — named from its square sliape and its insertion into 

 the femur — is a four-sided sheet. 



Origin. — The upper part of the outer border of the tuber ischii. 



Insertion. — The vertical ridge -vvliich begins just above the middle of the pos- 

 terior intertrochanteric line of the femur, and is called the 'linea quadrati.' 



Structure. — Its fibres are fleshy and run parallel to one another almost hori- 

 zontally outwards and slightly forwards. 



Nerve-supply. — From the sacral plexus (through the fifth lumbar and first 

 sacral nerve) by a special branch which, after furnishing filaments to the inferior 

 gemellus, enters the muscle near the upper part of its anterior surface close to its 

 origin. 



Action. — If approximates the posterior border of the greater trochanter to the 

 tuber iscliii, and so assists powerfully in the external rotation of the femur. 



Relations. — Behind, the gluteus maximus and the two sciatic nerves; in front, 

 the obturator externus and the termination of the internal circumflex artery. 

 Above is the inferior gemellus, and below tlie adductor magnus. 



Variations. — This muscle is not uufrequently absent. 



G. OBTURATOR EXTERNUS 



The obturator externus is a strong external rotator of the thigh, Init it is 

 also an adductor, and on account of its nerve-supply and position it is better 

 described in that group of muscles. 



THE ADDUCTORS 



The adductor muscles form a distinct group on the inner side of the thigh, 

 and are all supplied by the obturator nerve with the exception of a small part of 

 the adductor magnus. They consist of the adductor longus, adductor brevis, 

 adductor magnus, gracilis, and obturator externus. 



1. ADDUCTOR LONGUS 



The adductor longus — so named from its action and its length compared with 

 that of its immediate neighbour — is a thick triangular sheet. 



Origin. — A rounded impression on the front of the body of the os pubis 

 immediately below the crest and angle. 



Insertion. — (1) The lower two-thirds of the inner lip of the linea aspera (in 

 the middle third of the thigh) ; and (2) the adjacent internal intermuscular septum. 



Structure. — Arising by a strong rounded tendon, -which extends about two 

 inches (5 cm.) downwards upon the inner border of the muscle, the fleshy fil^res 

 diverge in a fan-shaped expansion, and are inserted by short tendinous fibres Avhich 

 blend behind with those of the adductor brevis and adductor magnus. 



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

 ])ranches from the anterior division of the obturator nerve which enter the muscle 

 on the up})cr part of its posterior surface rather below its middle. 



Action. — To adduct and flex the femur, and at the same time to rotate it 

 outwards. 



Relations. — In front, the fascia lata, sartorius, vastus internus, and superficial 

 femoral vessels; l)ehind, the adductor brevis and magnus, the profunda vessels, and 

 the obturator nerve; its upper border touches the i)ectineus. 



Variations. — The adductor loncfus may arise by two heads, the outer being attached to the 

 crest uf the pubes, and separate from the ordinary head which arises below the angle. Occa- 

 sionally the muscle is divided by the passage of vessels into an upper and a lower portion. 



