THE GREAT SCIATIC NERVE. 331 



trochanterand the ischial tuberosity, covered by the gluteus maximus and resting on 

 the gemelli, obturator internus, and quadratus femoris muscles, in company with the- 

 small sciatic nerve and the sciatic artery, and receiving from that artery a branch 

 which runs for some distance in its substance. Lower down it rests on the 

 adductor magnus, and is covered behind by the loug head of the biceps muscle. 



f Branches. In its course downwards, the great sciatic nerve supplies offsets to 

 the hamstring muscles, viz., the semitendinosus, two heads of the biceps, and 

 semimembranosus. A branch is likewise given to the inner part of the adductor 

 magnus. 



The branches of the great sciatic nerve to the muscles arising from the ischial tuberosity 

 are associated with its internal popliteal division, from which, however, they may be separated 

 up to their origin from the sacral plexus. They are then found to arise in the following^ 

 order from above downwards : the nerves to the adductor magnus (from 4 and 5 Z) and 

 semimembranosus (4, 5J and 1 *)> these being- commonly united in one cord ; two branches 

 for the semitendinosus (from 5 /, 1 and 2 xj, one supplying- the part of the muscle above, and 

 the other the part below the tendinous inscription ; and the nerve of the long head of the- 

 biceps (from 1, 2 and 3 *). The nerve of the short head of the biceps is united with the 

 external popliteal division, and according to Paterson may be followed up to 5 I, 1 and 2 s. 



Varieties. The bifurcation of the great sciatic nerve may take place at any point 

 intermediate between the sacral plexus and the lower part of the thigh ; and in some cases 

 the two popliteal nerves arise separately from the sacral plexus (see p. 324). Very rarely the 

 division takes place below the popliteal space (Henle). A branch of the great sciatic to join 

 the small sciatic on the back of the thigh is said to be normal by Krause, of frequent occurrence 

 by Henle. In one instance a nerve to the short head of the biceps arose directly from the 

 sacral plexus in union with the inferior gluteal nerve (G-. D. T.). 



Internal popliteal nerve. The internal popliteal (n. tibialis), the larger 

 of the two divisions of the great sciatic nerve, following the same direction as 

 the parent trunk, continues along the middle of the popliteal space to the lower 

 border of the popliteus muscle, beyond which point the continuation of the trunk 

 receives the name of posterior tibial. The internal popliteal nerve lies at first at 

 a considerable distance from tfye popliteal artery, at the outer side and nearer to 

 the surface ; but, from the km e-joint downwards, the nerve, continuing a straight 

 course, is close behind the artery, and then crosses it rather to the inner side. 



Branches. The internal popliteal nerve supplies branches to the knee-joint and to 

 the muscles of the calf of the leg, and also part of a cutaneous branch, the external 

 or short saphenous nerve. 



(a) The articular branches are given off from the upper part of the popliteal 

 trunk, and are generally three in number ; two of them accompany the upper and 

 lower articular arteries of the inner side of the knee-joint, the third follows the 

 middle or azygos artery. These nerves pierce the ligamentous tissue of the joint. 

 The upper one is often wanting. 



(b) The muscular branches arise from the nerve while it is contained in the 

 popliteal space. They include two nerves to the gastrocnemius (1, 2 s) one to each 

 head of the muscle ; a small nerve to the plantaris (4, 5 /, 1 s), derived either from 

 the branch to the outer head of the gastrocnemius, or directly from the main trunk ; a 

 considerable branch to the soleus (57, 1, 2 s), which enters the muscle on its posterior 

 aspect, close to the upper border ; and a nerve to the popliteus (4, 5 /, Is). The 

 last branch arises somewhat lower down, and is more deeply placed, than the others ; 

 it descends on the outer side of the popliteal vessels, gives off filaments to the 

 superior tibio-fibular articulation, to the tibia, and to the interosseous membrane, 

 and then turns beneath the lower border of its muscle, which it penetrates on the 

 deep or anterior surface. The branch to the tibia enters the shaft of the bone with 

 the medullary artery : that to the interosseous membrane is a long slender 



