960 NEUROLOGY 



the pelvis through the greater sciatic foramen below the Piriformis. It then descends 

 beneath the Glutseus maximus with the inferior gluteal artery, and runs down the 

 back of the thigh beneath the fascia lata, and over the long head of the Biceps 

 femoris to the back of the knee; here it pierces the deep fascia and accompanies 

 the small saphenous vein to about the middle of the back of the leg, its terminal 

 twigs communicating with the sural nerve. 



Its branches are all cutaneous, and are distributed to the gluteal region, the peri- 

 neum, and the back of the thigh and leg. 



The gluteal branches (nn. cluniuminferiores), three or four in number, turn upward 

 around the lower border of the Glutaeus maximus, and supply the skin covering 

 the lower and lateral part of that muscle. 



The perineal branches (rami perineales) are distributed to the skin at the upper 

 and medial side of the thigh. One long perineal branch, inferior pudenda! (long 

 scrotal nerve) , curves forward below and in front of the ischial tuberosity, pierces 

 the fascia lata, and runs forward beneath the superficial fascia of the perineum to 

 the skin of the scrotum in the male, and of the labium majus in the female. It 

 communicates with the inferior hemorrhoidal and posterior scrotal nerves. 



The branches to the back of the thigh and leg consist of numerous filaments derived 

 from both sides of the nerve, and distributed to the skin covering the back and 

 medial side of the thigh, the popliteal fossa, and the upper part of the back of the 

 leg (Fig. 830). 



The Sciatic (n. ischiadicus; great sciatic nerve) (Fig. 832) supplies nearly the whole 

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

 and foot. It is the largest nerve in the body, measuring 2 cm. in breadth, and is 

 the continuation of the flattened band of the sacral plexus. It passes out of the 

 pelvis through the greater sciatic foramen, below the Piriformis muscle. It descends 

 between the greater trochanter of the femur and the tuberosity of the ischium, and 

 along the back of the thigh to about its lower third, where it divides into two large 

 branches, the tibial and common peroneal nerves. This division may take place 

 at any point between the sacral plexus and the lower third of the thigh. When it 

 occurs at the plexus, the common peroneal nerve usually pierces the Piriformis. 



In the upper part of its course the nerve rests upon the posterior surface of the 

 ischium, the nerve to the Quadratus femoris, the Obturator internus and Gemelli, 

 and the Quadratus femoris; it is accompanied by the posterior femoral cutaneous 

 nerve and the inferior gluteal artery, and is covered by the Glutaeus maximus. 

 Lower down, it lies upon the Adductor magnus, and is crossed obliquely by the 

 long head of the Biceps femoris. 



The nerve gives off articular and muscular branches. 



The articular branches (rami articulares) arise from the upper part of the nerve 

 and supply the hip-joint, perforating the posterior part of its capsule; they are 

 sometimes derived from the sacral plexus. 



The muscular branches (rami musculares) are distributed to the Biceps femoris, 

 Semitendinosus, Semimembranosus, and Adductor magnus. The nerve to the short 

 head of the Biceps femoris comes from the common peroneal part of the sciatic, 

 while the other muscular branches arise from the tibial portion, as may be seen in 

 those cases where there is a high division of the sciatic nerve. 



The Tibial Nerve (n. tibialis; internal popliteal nerve) (Fig. 832) the larger of the 

 two terminal branches of the sciatic, arises from the anterior branches of the 

 fourth and fifth lumbar and first, second, and third sacral nerves. It descends 

 along the back of the thigh and through the middle of the popliteal fossa, to the lower 

 part of the Popliteus muscle, where it passes with the popliteal artery beneath the 

 arch of the Soleus. It then runs along the back of the leg with the posterior 

 tibial vessels to the interval between the medial malleolus and the heel, where it 

 divides beneath the laciniate ligament into the medial and lateral plantar nerves. 



