GREAT SCIATIC. 659 



and back part of the thigh and leg, and one muscle, the Gluteus Maximus. It 

 is usually formed by the union of two branches, which arise from the lower 

 part of the sacral plexus. It issues from the pelvis below the Pyriformis mus- 

 cle, descends beneath the Gluteus Maximus with the sciatic artery, and at the 

 lower border of that muscle passes along the back part of the thigh, beneath 

 the fascia lata, to the lower part of the popliteal region, where it pierces the 

 fascia and becomes cutaneous. It then accompanies the external saphenous 

 vein below the middle of the leg, its terminal filaments communicating with 

 the external saphenous nerve. 



The branches of the small sciatic nerve are muscular (inferior gluteal) and 

 cutaneous. 



The inferior gluteal consist of several large branches given off to the under 

 surface of the Gluteus Maximus, "near its lower part. 



The cutaneous branches consist of two groups, internal and ascending. 

 The internal cutaneous branches are distributed to the skin at the upper and 

 inner side of the thigh, on its posterior aspect. One branch, longer than the 

 rest, the inferior pudendal, curves forward below the tuber ischii, pierces the 

 fascia lata on the outer side of the ramus of the ischium, and is distributed to 

 the integument of the scrotum, communicating with the superficial perineal 

 nerve. 



The ascending cutaneous branches consist of two or three filaments, which turn 

 upwards round the lower border of the Gluteus Maximus, to supply the integu- 

 ment covering its surface. One or two filaments occasionally descend along 

 the outer side of the thigh, supplying the integument as far as the middle of 

 that region. 



Two or three branches are given off from the lesser sciatic nerve as it de- 

 scends beneath the fascia of the thigh ; they supply the integument of the back 

 part of the thigh, popliteal region, and upper part of the leg. 



The Great Sciatic Nerve (Fig. 358) supplies nearly the whole of the integu- 

 ment of the leg, the muscles of the back of the thigh, and those of the leg and 

 foot. It is the largest nervous cord in the body, measuring three-quarters of 

 an inch in breadth, and is the continuation of the lower part of the sacral 

 plexus. It passes out of the pelvis through the great sacro-sciatic foramen, 

 below the Pyriformis muscle. It descends between the trochanter major and 

 tuberosity of the ischium, along the back part of the thigh to about its lower 

 third, where it divides into two large branches, the internal and external popli- 

 teal nerves. 



This division may take place at any point between the sacral plexus and the 

 lower third of the thigh. When the division occurs at the plexus, the two 

 nerves descend together, side by side ; or they may be separated, at their com- 

 mencement, by the interposition of part or the whole of the Pyriformis muscle. 

 As the nerve descends along the back of the thigh, it rests at first upon the 

 external rotator muscles, together with the small sciatic nerve and artery, being 

 covered by the Gluteus Maximus ; lower down, it lies upon the Adductor Mag- 

 nus, and is covered by the long head of the Biceps. 



The branches of the nerve, before its division, are articular and muscular. 

 The articular branches arise from the upper part of the nerve ; they supply 

 the hip-joint, perforating its fibrous capsule posteriorly. These branches are 

 sometimes derived from the sacral plexus. 



The muscular branches are distributed to the flexors of the leg ; viz., the 

 Biceps, Semitendinosus, and Semimembranosus, and a branch to the Adductor 

 Magnus. These branches are given off beneath the Biceps muscle. 



The Internal Popliteal Nerve, the larger of the two terminal branches of the 

 great sciatic, descends along the back part of the thigh through the middle of 

 the popliteal space, to the lower part of the Popliteus muscle, where it passes 

 with the artery beneath the arch of the Soleus, arid becomes the posterior tibial. 

 It lies at first very superficial, and at the outer side of the popliteal vessels ; 



