THE SACRAL PLEXUS. 791 



f Muscular. 

 | Superior gluteal. 



Collateral branches -( Inferior gluteal. 

 j Small sciatic. 

 [ Perforating cutaneous. 



Terminal branches < ^ 



[ Great sciatic. 



The Muscular branches supply the Pyriformis, Obturator internus, the two 

 Gemelli, and the Quadratus femoris. The branch to the Pyriformis arises from 

 the upper two sacral nerves before they enter the plexus ; the branch to the 

 Obturator internus arises at the junction of the lumbo-sacral and first sacral 

 nerves : it passes out of the pelvis through the great sacro-sciatic foramen below 

 the Pyriformis, crosses the spine of the ischium, arid re-enters the pelvis through 

 the lesser sacro-sciatic foramen to enter the inner surface of the Obturator internus ; 

 the branch to the Gemellus superior arises in common with the nerve to the Obtu- 

 rator internus : it enters the muscle at the upper part of its posterior surface ; the 

 small branch to the Gemellus inferior and Quadratus fcmoris also arises from the 

 upper part of the plexus : it passes through the great sacro-sciatic foramen below 

 the Pyriformis, and courses down beneath the great sciatic nerve, the Gemelli and 

 tendon of the Obturator internus, and supplies the muscles on their deep or ante- 

 rior surface. It gives off an articular branch to the hip-joint. A second articular 

 branch is occasionally derived from the upper part of the sacral plexus. 



The Superior Gluteal Nerve (Fig. 423) arises from the back part of the lumbo- 

 sacral cord, with some filaments from the first sacral nerve ; it passes from the 

 pelvis through the great sacro-sciatic foramen above the Pyriformis muscle, accom- 

 panied by the gluteal vessels, and divides into a superior and an inferior branch. 



The superior branch follows the line of origin of the Gluteus minimus, and 

 supplies the Gluteus medius. 



The inferior branch crosses obliquely between the Gluteus minimus and medius, 

 distributing filaments to both these muscles, and terminates in the Tensor fasciae 

 femoris, extending nearly to its lower end. 



The Inferior Gluteal arises from the lumbo-sacral cord and first and second 

 sacral nerves, and is intimately connected with the small sciatic at its origin. 

 It passes out of the pelvis through the great sciatic notch, beneath the Pyriformis 

 muscle, and, dividing into a number of branches, enters the Gluteus maximus 

 muscle on its under surface. 



The Small Sciatic Nerve (Fig. 423) supplies the integument of the perineum 

 and back part of the thigh and leg. It is usually formed by the union of two 

 branches, which arise from the second and third nerves of the sacral plexus. It 

 issues from the pelvis through the great sacro-sciatic foramen below the Pyriformis 

 muscle, 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 and over the long head of the Biceps, to the lower part of the popliteal 

 region, where it pierces the fascia and becomes cutaneous. It then accompanies 

 the external saphenous vein to about the middle of the leg, its terminal filaments 

 communicating with the external saphenous nerve. 



The branches of the small sciatic nerve are all cutaneous, and are grouped as 

 follows : gluteal, perineal, and femoral. 



The gluteal cutaneous branches (ascending} consist of two or three filaments, 

 which turn upward round the lower border of the Gluteus maximus to supply the 

 integument covering the lower and outer part of that muscle. 



The perineal 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, and passes forward beneath the superficial fascia of the perineum to be dis- 

 tributed to the integument of the scrotum in the male and the labium in the female, 

 communicating with the superficial perineal and inferior hemorrhoidal nerves. 



