SCIATIC PLEXUS 197 



which passes through the sacro -sciatic foramen as the great 

 sciatic nerve, which supplies the back of the thigh and the 

 whole of the leg and foot (excepting that part of skin supplied 

 by the saphenous nerve) ; small branches arise from the anterior 

 and posterior surfaces of the plexus to supply the parts in the 

 vicinity. The great sciatic nerve ends at the popliteal space By 

 dividing into tibial and peroneal nerves (internal and external 

 popliteal nerves). In reality this division can be traced all the 

 way up to the plexus, so that the nerve is really constituted in 

 two parts, but for purposes of description it is easier to call the 

 upper part one trunk namely, the great sciatic. 



The plexus is formed by the lower part of the fourth lumbar 

 nerve joining the fifth lumbar nerve, which, known as the lumbo- 

 sacral cord, passes into the pelvis over the sacro-iliac articulation, 

 and on pyriformis joins the first and second and upper part of 

 third sacral nerves. The three sacral nerves also send branches 

 to the pudendal plexus, so that no distinct line can be drawn 

 between them. 



Branches from the plexus (other than great sciatic) : 



Anterior. Muscular to quadratus femoris, obturator internus 

 and gemelli. 



Articular to hip- joint. 



Posterior. Muscular to pyriformis and glutei (superior and 

 inferior gluteal nerves). 



Articular to knee-joint (via the nerve to biceps) . 



Cutaneous to skin on back of thigh (small sciatic). 



Superior Gluteal nerve arises from the fourth and fifth 

 lumbar and the first sacral nerves. It passes through the 

 sacro-sciatic foramen, with the gluteal artery above pyriformis, 

 and supplies gluteus medius and minimus and tensor fasciae 

 femoris. 



Inferior Gluteal nerve arises from the fifth lumbar and first 

 and second sacral nerves. It passes through the sacro-sciatic 

 foramen beneath pyriformis, and supplies gluteus niaximus. 



Small Sciatic nerve passes through the sacro-sciatic foramen 

 below pyriformis, with the sciatic artery and inferior gluteal 

 nerve. It enters the thigh at the lower border of gluteus maxi- 

 nius, and, piercing the deep fascia, it supplies the skin on the 



