BRANCHES OF THE SACRAL PLEXUS. 121 



to one or two filaments to the hip-joint. Frequently the nerve is 

 divided into two large trunks at its origin, and one of them (the 

 external popliteal) pierces the fibres of the pyrifornds muscle. 



The PUDIC NERVE (fig. 48) winds over the small sacro-sciatic Pudic nerve, 

 ligament on the inner side of its companion artery, and is dis- 

 tributed with this vessel to the perineum and the genital organs. 

 Xo branch is supplied to the buttock. 



Small MUSCULAR BRANCHES of the sacral plexus are furnished to Muscular 

 the external rotators except the obturator externus. 



The branch to the pyriformis, from the second sacral nerve, is to 

 seen in the dissection of the sacral plexus in the pelvis. pyriformis ; 



The nerve to the obturator interims (fig. 50, 5 ) arises from the to obturator 

 upper part of the plexus, and is directed to its muscle through jJJjJSiOT *"' 

 the small sacro-sciatic foramen external to the pudic vessels : it gemeiius ; 

 gives off a small twig to the superior gemeiius ( 7 ). 



The nerve to the quadratus femoris (fig. 50, 6 ) is a slender branch, toquad- 

 which passes with a companion artery beneath the gemelli and the !Jf25i m 

 obturator to the anterior surface of its muscle. This branch will gemeiius. 

 be seen more fully in a subsequent dissection, when offsets from it 

 to the inferior gemeiius and the hip-joint may be traced. 



Dissection. To see the remaining external rotator muscles, hook Clean rota- 

 aside the great sciatic nerve, and take away the branches of the 

 sciatic artery if it is necessary. In cleaning these muscles the 

 limb should be rotated inwards. The gemelli are to be separated 

 from the tendon of the obturator internus. 



The SUPERIOR GEMELLUS (fig. 48, c) is the higher of the two Superior 

 muscular slips along the sides of the tendon of the obturator s emellus - 

 muscle. Internally it arises from the outer and lower part of the 

 ischial spine (fig. 47, p. 113), and externally it is inserted with the 

 obturator into the great trochanter. Occasionally the muscle is 

 absent. 



The INFERIOR GEMELLUS (fig. 48, E) is larger than its fellow, inferior 

 Its origin is connected with the upper part of the ischial tuberosity, gem 

 along the lower edge of the groove for the obturator interims muscle 

 (fig. 47) ; and its insertion is in common with the obturator tendon. 

 This muscle is placed between the obturator internus and quad- both in- 

 ratus, but near the femur the tendon of the obturator externus obturator 1 - 11 

 comes into contact with its upper border. 



Action. These small fleshy slips are but accessory pieces of use to help 

 origin to the internal obturator, with which they combine in use. obturator. 



The OBTURATOR INTERNUS (fig. 48, D) arises from the hip-bone obturator 

 inside the pelvis, and passes to the exterior through the small mternus 

 sacro-sciatic foramen. The tendon of the muscle is directed outside 

 outwards over the hip-joint, and is inserted with the gemelli, in p 

 front of the pyriformis, into the inner side of the great trochanter, m 

 at the upper and fore part (fig. 60, p. 157). 



Outside the pelvis the obturator is mostly tendinous, and is relations; 

 embraced by the gemelli muscles, which near the pelvis meet 

 beneath the tendon ; but near the trochanter they cover it. 

 Crossing the muscle are the large and small sciatic nerves and the 



