422 GREAT ISCHIATIC NERVE. 



municating branch which pierces the fascia of the leg and unites 

 with the external saphenous nerve. 



The GREAT ISCHIATIC NERVE is the largest nervous cord in the 

 body ; it is formed by the sacral plexus, or rather it is a prolonga- 

 tion of the plexus, and at its exit from the great sacro-ischiatic fora- 

 men beneath the pyriformis muscle measures three quarters 01 an 

 inch in breadth. It descends through the middle of the space 

 between the trochanter major and tuberosity of the ischium, and 

 along the posterior part of the thigh to about its lower third, where 

 it divides into two large terminal branches, popliteal and peroneal. 

 This division sometimes takes place at the plexus, and the two 

 nerves descend together side by side ; occasionally they are sepa- 

 rated at their commencement by a part or the whole of the pyri- 

 formis muscle. The nerve in its course down the thigh rests upon 

 the gemellus superior, tendon of the obturator internus, gemellus 

 inferior, quadratus femoris, and adductor magnus muscle, and is 

 covered in by the gluteus maximus, and by the biceps and semiten- 

 dinosus muscle. 



The Branches of the great ischiatic nerve, previously to its divi- 

 sion, are muscular and articular. The muscular branches are given 

 off from the upper part of the nerve and supply the biceps, the semi- 

 tendinosus, the semi-membranosus, and the adductor magnus. The 

 articular branch descends to the upper part of the external condyle 

 of the femur, and divides into filaments which are distributed to the 

 fibrous capsule and to the synovial membrane of the knee-joint. 



The POPLITEAL NERVE passes through the middle of the popliteal 

 space, from the division of the great ischiatic nerve to the lower 

 border of the popliteus muscle, where it passes with the artery 

 beneath the arch of the soleus, and becomes the posterior tibial 

 nerve. It is superficial in the whole of its course, and lies exter- 

 nally to the vein and artery. 



The Branches of the popliteal nerve are muscular or sural and 

 articular, and a cutaneous branch the communicans poplitei. 



The Muscular branches, of considerable size, and four or five in 

 number, are distributed to the two heads of the gastrocnernius, to 

 the soleus, to the plantaris, and to the popliteus. 



The Articular nerve pierces the ligamentum posticum Winslowi, 

 and supplies the interior of the knee-joint. It usually sends a twig 

 to the popliteus muscle. 



The Communicans poplitei is a large nerve which arises from the 

 popliteal at about the middle of its course, and descends between 

 the two heads of the gastrocnemius, and along the groove formed 

 by the two bellies of that muscle ; at a variable distance below the 

 articulation of the knee it receives a large branch, the communicans 

 peronei, from the peroneal nerve, and the two together constitute 

 the external saphenous nerve. 



The External saphenous nerve pierces the deep fascia below the 

 fleshy part of the gastrocnemius muscle, and continues its course 

 down the leg, lying along the outer border of the tendo Achillis and 



