THE LUMBAR PLEXUS 169 



passing through the uppermost part of the obturator foramen, 

 and in this way it gains the medial compartment of the thigh. 

 The branches of the obturator nerve are distributed (i) to 

 the obturator externus and to the adductor group of muscles ; 

 (2) to the hip- and knee-joints ; and (3) to the skin over the 

 medial aspect of the thigh. 



The Obturator Externus arises from the outer surface of the obturator 

 membrane and, passing first below and then behind the capsule of the hip- 

 joint, is inserted into the trochanteric fossa. It is a powerful lateral rotator 

 of the thigh, but its paralysis cannot be satisfactorily demonstrated, because 

 (i) the muscle is so deeply placed that the examination of its contractility 

 or its electrical reactions is practically impossible, and (2) the thigh is 

 furnished with several lateral rotator muscles, e.g. obturator internus, 

 quadratus femoris, etc., which are supplied by the sacral plexus. 



The Addtictor Group consists of the Adductors Longus, Brevis and 

 Magnus and the Gracilis. 



The Adductors Longus and Brevis extend from the pubis to the dorsal 

 aspect of the shaft of the femur. They are powerful adductors and they 

 assist in flexing the hyperextended thigh. 



The Adductor Magnus arises from the pubis and its origin extends back- 

 wards on to the ischial tuberosity. It is inserted into the whole length of 

 the dorsal aspect of the femur, and, distally, it reaches the adductor tubercle 

 on the medial condyle. The fibres which arise from the pubis are attached 

 to the proximal part of the femur, whereas those which arise from the 

 ischial tuberosity run almost vertically to gain the adductor tubercle. On 

 account of the arrangement of its fibres, the action of the adductor magnus 

 is slightly complicated. 



Acting as a whole, the muscle is a powerful adductor. The upper 

 fibres help to flex the hyperextended thigh, but the lower fibres help to 

 extend the flexed thigh. In consequence of the latter action, the 

 adductor magnus receives an additional nerve of supply, from the sciatic 

 nerve. 



The Gracilis arises from the pubis and passes distally along the medial 

 aspect of the thigh to be inserted into the proximal part of the antero- 

 medial surface of the tibia. It is a weak adductor and flexor of the hip, 

 but it assists in flexion and medial rotation of the knee (p. 175). 



The Articular Branches help to supply the synovial mem- 

 brane of the hip- and knee-joints, but the genicular branch is 

 by no means constant. It appears likely that pain referred 

 from the hip-joint to the region of the knee has no connexion 



