POPLITEAL NERVE. 477 



the plexus, and at its exit from the great sacro-ischiatic foramen be- 

 neath the pyriformis muscle measures three quarters of 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 some- 

 times takes place at the plexus, and the two nerves descend together 

 side by side ; occasionally they are separated at their commencement 

 by a part or the whole of the pyriformis 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, biceps, 

 semitendinosus, and semimembranosus. 



The Branches of the great ischiatic nerve, previously to its division, 

 are muscular and articular. The muscular branches are given off from 

 the upper part of the nerve and supply both heads of the biceps, the 

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

 ticular 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, accompanies 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 externally to the vein and artery. 



The Branches of the popliteal nerve are muscular or sural, and ar- 

 ticular, 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 gastrocnemius, to the 

 soleus, plantaris, and popliteus. 



The Articular nerve pierces the ligamentum posticum Winslowii, 

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

 to the popliteus muscle. 



The Communicans poplitei (communicans tibialis) 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 com- 

 municans peronei, from the peroneal nerve, and the two together con- 

 stitute 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 

 by the side of the external saphenous vein which it accompanies to 

 the foot. At the lower part of the leg it winds around the outer 

 malleolus, and is distributed to the outer side of the foot and little 

 toe, communicating with the external peroneal cutaneous nerve, 



