774 THE NERVES. 



principal branches are lost in the middle gluteal muscle. One of them 

 (Fig. 356, 4,) crosses the neck of the ilium above the small (or internal) 

 gluteal muscle, and passes outwards to be distributed to the muscle of the 

 fascia lata (tensor vaginae femoris). The last, which is the most slender, 

 descends to the external surface of the gluteus iuternns, and is distributed in 

 its substance (Fig. 356, 5). 



The posterior gluteal, or iscliio-muscular nerves (Fig. 356, 6, 6', 8), are 

 usually two in number a superior and inferior. 



The first escapes through the great sacro-ischiatic notch, along with the 

 femoro-popliteal nerves, and is situated on the external surface of the ischiatic 

 ligament. It passes backward, between this ligament and the gluteus 

 medius, to beneath the anterior or croupal portion of the triceps extensor 

 cruris, in which it is distributed by several filaments. Besides these, it 

 gives : 1, In passing beneath the gluteus medius, a slender, but constant 

 filament to the posterior portion of that muscle; 2, Another, and more 

 considerable branch, which bends round the posterior border of that 

 muscle, to be directed forward and outward to the gluteus extern us. 



The second nerve, situated beneath the preceding, appears to be detached 

 from the posterior border of the great sciatic. It is placed at the extornal 

 surface of the sciatic ligament, is directed backwards in passing below the 

 croupal portion of the triceps cruris, traverses that muscle above the ischial 

 tuberosity, descending underneath the sacral portion of the semitendinosus, 

 soon to leave its deep track and become superficial. It escapes from between 

 the latter muscle and the triceps cruris, and is lost beneath the skin covering 

 the posterior part of the thigh. Its deep portion gives off collateral 

 branches which reinforce the divisions of the internal pudic nerve, as well 

 as filaments to the long branch of the semitendinosus muscle. 



5. Great Sciatic or Great Femoro-popliteal Nerve. (Figs. 135, 1 3 ; 357, 1, 2.) 



This enormous nervous trunk' issues by the great sciatic opening in the 

 form of a wide band, which is applied to the external face of the ischiatic 

 ligament. Comprised at first between that ligament and the gluteus medius, 

 it is directed backwards in passing over the fixed insertion of the gluteus 

 internus, and arrivos behind the gemini and quadrat us femoris muscles. On 

 leaving this point, it is inflected to descend behind the thigh, where it is 

 lodged in the muscular sheath formed for it by the triceps cruris, the semi- 

 tendinosus and membranosus, and the great adductor of the thigh. Arriving 

 towards the superior extremity of the leg, it enters between the two bellies 

 of the gastrocnemii muscles, passes along the posterior aspect of the 

 perforatus muscle, and descends in the channel of the hock, beneath the tibial 

 aponeurosis, following the internal border of the fibrous band that rein- 

 forces the tendon of the hock. It finally terminates at the calcis by two 

 branches ; the external and internal plantar nerves. 



From the point at which the great sciatic enters between the bellies of 

 the gastrocnemii muscles, and as far as the furrow of the calcis, this nerve 

 corresponds to the branch named in Man the internal popliteal a branch 

 that is continued by the posterior tibial, which terminates in the plantar 

 filaments. 



In its long course, this nerve successively emits: 1, The external 

 popliteal nerve ; 2, A branch to the muscles of the deep pelvi-crural region ; 

 3, Another to the posterior crural muscles; 4, The external saphenous 

 nerve; 5, A voluminous fasciculus to the muscles of the posterior tibia! 



