GREAT SCIATIC NERVE. 675 



trochanter major, points to the tendon of the obturator internus ; e, upper part of the 

 femoral head of the biceps; f, semitendinosus ; g, semimembranosus ; h, gastrocnemins ; 

 i, popliteal artery; 1, placed on the gluteus minimus muscle, points to the superior 

 gluteal nerves ; 2, inferior gluteal branches of the lesser sciatic; 3, placed on the greater 

 sacro- sciatic ligament, points to the pudic nerve ; 3', its farther course ; 4, inferior 

 pudendal ; 5, placed on the upper divided part of the semitendinosus and biceps, points 

 to the posterior middle cutaneous nerve of the thigh ; 6, great sciatic nerve, 6', 6', some 

 of its muscular branches to the flexors ; 7, internal popliteal or posterior tibial nerve ; 7', 

 its muscular or sural branches ; 8, external popliteal or peroneal nerve ; 8', its external 

 cutaneous branch ; 9, communicating tibial ; &', communicating peroneal branch to the 

 external saphenous nerve. 



The inferior pudendal branch turns forwards below the ischial tuberosity to reach 

 the perinseum. Its filaments then extend forwards to the front and outer part of the 

 scrotum, and communicate with one of the superficial perineal nerves. In the female, 

 the inferior pudendal branch is distributed to the external labium pudendi. 



b. The external cutaneous branches, two or three in number, turn upwards in a 

 retrograde course to the skin over the lower and outer part of the great gluteal 

 muscle. In some instances one takes a different course, descending and ramifying 

 in the integuments on the outer side of the thigh nearly to the middle. 



c. Of the lower branches some small cutaneous filaments pierce the fascia of the 

 thigh above the popliteal space. One of these, arising somewhat above t'he knee-joint, 

 is prolonged over the popliteal region to the upper part of the leg. 



Of the terminal twigs, perforating the fascia lata opposite the lower part of the 

 popliteal space, one accompanies the short saphenous vein beyond the middle of the 

 leg, and others pass into the integument covering the inner and outer heads of the 

 gastrocnemius muscle. Its terminal cutaneous branches communicate with the short 

 saphenous nerve. 



GREAT SCIATIC NERVE. 



The great sciatic nerve (nervus ischiadicus), the largest nerve in the body, 

 supplies the muscles at the back of the thigh, and by its branches of con- 

 tinuation gives nerves to all the muscles below the knee and to the greater 

 part of the integument of the leg and foot. The several joints of the 

 lower limb receive filaments from it and its branches. 



This large nerve is continued from the lower end of the sacral plexus. It 

 escapes from the pelvis through the great sacro-sciatic foramen, below the pyri- 

 formis muscle, and reaches down below the middle of the thigh, where it 

 separates into two large divisions, named the internal and external popliteal 

 nerves. At first it lies in the hollow between the great trochauter and the 

 ischial tuberosity, covered by the gluteus maximus and resting on the 

 gemelli, obturator internus and quadratus femoria muscles, in company with 

 the small sciatic nerve and the sciatic artery, and receiving from that artery a 

 branch which runs for some distance in its substance. Lower down it rests 

 on the adductor magnus, and is covered behind by the long head of the 

 biceps muscle. 



The bifurcation of the sciatic nerve may take place at any point intermediate 

 between the sacral plexus and the lower part of the thigh ; and, occasionally, it is 

 found to occur even within the pelvis, a portion of the pyriformis muscle being inter- 

 posed between the two great divisions of the nerve. 



Branches of the trunk. In its course downwards, the great sciatic nerve 

 supplies offsets to some contiguous parts, viz., to the hip-joint, and to the 

 muscles at the back of the thigh. 



a. The articular branches are derived from the upper end of the nerve, and enter 

 the capsular ligament of the hip-joint, on the posterior aspect. They sometimes arise 

 from the sacral plexus. 



