THE GEEAT SCIATIC NERVE. 615 



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

 femoral head of the biceps ; /, semitendinosus ; q, semimembranosus ; h, gastrocnemius ; 

 i, popliteal artery; 1, placed on the ghiteus 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, gi-eat sciatic nerve, 6', 6', some 

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

 or sural branches ; 8, external popliteal nerve ; 8', its external cutaneous branch ; 

 9, communicating tibial ; 9', communicating peroneal branch to the external saphenous 

 nerve. 



In the female, the inferior pudendal branch is distributed to tlie external labium 

 pudendi. 



h. 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 coiu-se, descending and ramify- 

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



c. Of the loiver hrancJicn some small cutaneous filaments pierce the fascia of 

 the thigh above the popliteal space. One of these, arising somewhat above the 

 knee-joint, is prolonged over the popliteal region to the upper part of the leg. 



Of the terminal tn-igs, perforating the fascia lata oppasite the lower part of the 

 l^opliteal 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 shoii; so.phenous nerv^e. 



Great Sciatic Nerve. 



The great sciatic nerve (nervus ischiadicus major), the largest nerve 

 in the body, supplies the muscles at the back of the thigh, and by its 

 branches of continuation 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 pyriformis muscle, and reaches down below the middle of the 

 thigh, where it separates into two large divisions, named the internal 

 and external j^opliteal nerves. At first it lies in the hollow between the 

 great trochanter and the ischial tuberosity, covered by the ghiteus 

 maximus and resting on the gemelli, obturator intemus, and quadratus 

 femoris 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 

 interposed between the two great divisions of the nerve. 



BRAifCHES OF THE TRUNK. — In its coursc downwards, the great 

 sciatic nerve supplies ofisets to some contiguous parts, viz., to the hip- 

 joint, and to the muscles at the back of the thigh. 



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

 enter the capsular ligament of the hip-joint, on the posterior aspect. They some- 

 times arise from the sacral plexus. 



