THE SCIATIC NERVE 



1009 



into the common peroneal (external politeal) and the tibial (internal popliteal) 

 nerves (fig. 771). 



The relation of the trunk to the piriformis muscle is more or less unique. It may pass either 

 above or below the muscle, it may spht and pass around the muscle, or the muscle may be split 

 and surround the nerve. Again, there may be a sphtting of both the muscle and the nerve, in 

 which case any possible combination of the four parts may occur; a portion of the nerve may be 

 above and a portion between the parts of the muscle, or a portion may be below and a portion 

 between. The trunk of the nerve hes deeply in the thigh, and it is covered posteriorly by the 

 skin and fascia, the gluteus maximus and the long head of the biceps femoris. Anteriorly it 

 is in relation, from above downward, with the following structures: — the posterior surface of 

 the ischium and the nerve to the quadratus femoris, the gemellus superior, obturator internus, 

 gemellus inferior, quadratus femoris, and adductor magnus muscles. 



Muscular branches of the sciatic are given off at the upper part of the thigh to 

 the semitendinosus, to the long head of the biceps femoris, to the semimembranosus, 



Fig. 770. — A Dissection of the Nerves in the Gluteal Region. 

 (The gluteus maximus and gluteus medius have been divided near their insertions, and thrown 



upward.) 



Inferior gluteral artery 



.Gluteus maximus 



Inferior gluteal nerve 



Gluteal artery 



Branch to gluteus 

 maximus 



Pudic nerve 



Sacro-tuberous 

 ligament 



Comes nervi 



ischiadici 

 Gemellus 

 inferior 

 Tuberosity of 

 ischium 



Long pudendal 



Quadratus 

 V^ femoris 



^^^ Adductor 



magnus 



Nerve to 



tensor 



fasciae 



latse 



Tendon of obturator externus 





Sciatic nerve 



Posterior 

 cutaneous 

 nerve 



Vastus externus 



Gluteus maximus 



and to the adductor magnus, and, about the middle of the thigh, a branch is fur- 

 nished to the short head of the biceps. 



The branch to the short head of the biceps femoris is derived from the peroneal (lateral 

 popliteal) portion of the nerve, while all the other muscular branches are given off by the tibial 

 (medial popUteal) part. The semitendinosus receives two branches, one which enters it above 

 and another which passes into it below its tendinous intersection. The nerve to the long head 

 of the biceps descends along the sciatic trunk and enters the middle of the deep surface of the 

 muscle. The nerves to the semimembranosus and adductor magnus arise by a common trunk 

 which divides into three or four branches. One branch ends in the adductor, and the others 

 are distributed to the semimembranosus. The branch to the adductor magnus supphes only 

 those fibres of the muscle which begin from the tuberosity of the ischium and descend vertically 

 to the medial condyle of the femur. 



At the apex of the popliteal space the two component parts of the common 

 trunk of the sciatic become distinct. The tibial nerve (internal popliteal) , formed 

 by fibres from the anterior branches of the fourth and fifth lumbar and first, 

 second, and third sacral nerves, passes vertically through the popliteal space, 

 descends through the leg to a point midway between the medial malleolus and 

 the most prominent part of the medial tubercle of the os calcis, where it divides 

 into its terminal branches, the lateral plantar and the medial plantar nerves. 

 The part of the nerve from the point of bifurcation to the lower border of the 

 popliteus muscle is sometimes called the internal popliteal; the part of the nerve 

 in the dorsum of the leg being then designated the posterior tibial nerve. 



