PAEALY8IS OF THE GREAT SCIATIC NERVE. 241 



passes through the coraco-brachialis, supplying that muscle, 

 and then comes to lie beneath the biceps and upon the 

 brachialis anticus, both of which it innervates. Above the 

 elbow-joint it is not so very far internal to the musculo-spiral, 

 and when exposed may be mistaken for the latter nerve. 



The circumflex nerve is derived from the posterior cord of 

 the brachial plexus, and winds round the back of the surgical 

 neck of the humerus, supplying the deltoid and teres minor 

 muscles, together with the shoulder-joint and some of the skin 

 covering it. 



The nerve is liable to injury in fracture of the surgical neck, 

 separation of the upper epiphysis, and dislocation of the head of 

 the humerus. 



The Lower Extremity. Injury to the nerves of the lower 

 extremity is comparatively rare, but disease affecting the 

 function of these nerves is not infrequently seen. 



The great sciatic nerve emerges from the pelvis through 

 the great sacro-sciatic foramen below the pyriformis muscle, 

 at a point which may be roughly indicated upon a line 

 from the posterior superior spine of the ilium to the most pro- 

 minent part of the tuberosity of the ischium, at the junction of 

 the lower third with its upper two-thirds. Here it is deeply 

 placed under the gluteus maximus muscle, and can be con- 

 siderably stretched in complete flexion at the hip-joint especially 

 when the knee is kept extended. A little lower down it lies half- 

 way between the great trochanter and the tuber ischii, and deep 

 pressure here will give rise to severe pain when the nerve is 

 inflamed. Proceeding down the back of the thigh, it next lies 

 between the hamstrings and the vastus externus, dividing about 

 the middle into the peroneal or external popliteal, and the 

 internal popliteal nerves. 



The sciatic nerve is accompanied by an artery which may be 

 of great value in the formation of a collateral circulation after 

 ligature for femoral or external iliac aneurysms. 



The main trunk supplies the biceps, semimembranosus, 

 semitendinosus, and a portion of the adductor magnus. 



C.A.A. 16 



