GREAT SCIATIC NERVE 



707 



posterior head of the superficial gluteus. The inferior nerve runs downward and 

 l)ackward on the sacro-sciatic ligament and divides into the posterior cutaneous 

 nerve and muscular branches which supply the semitendinosus. The former (N. 

 cutaneus femoris caudalis) passes through the l^iceps femoris, emerges between 

 that muscle and the semitendinosus a little below the level of the tuber ischii, and 

 ramifies subcutaneously on the outer and posterior surfaces of the hip and thigh 

 (Fig. 525). 



Great Sciatic Nerve 



The great sciatic nerve (N. ischiadicus) (Figs. 451, 455, 526), the largest in 

 the body, is derived chiefly from the last lumbar and the sacral roots of the lumbo- 

 sacral plexus, but may receive a fasciculus from the third sacral nerve also. It 



Sacral spines 



Aponeurosis 

 of longissi- 

 mus dor si 



lumbar 

 vertehrce 



Coccygeal 

 vertebrae 



Lateral sacro- / yi'^, 



iliac ligament \ 



Sacro-scidI 

 ligament 



Mammillary 

 process 



Branches of anterior gluteal artery 

 and nerve 



~ A cetabular fossa 

 ~ Acetabular notch 



— Pubic eminence 



^Obturator artery 

 ^Obturator inter nus 

 ^Obturator vein 



Tuber 

 iscfiii 



Lesser Gemel- Anastomosis^ 

 sciatic lus between ob- 

 f or amen turator and 



internal pudic 

 veins 



Fig. 526. — Vessels and Nerves on Pelvic Wall of Horse. 

 Nerv-us ischiadicus = great sciatic nerve; n. glut. inf. = anterior gluteal nerve; n. pudeudus = internal pudic nerve. 



(After Schmaltz, Atlas d. Anat. d. Pferdes.) 



emerges through the great sacro-sciatic foramen as a broad flat band blended at 

 first with the posterior gluteal nerve— which passes downward and backward on 

 the lower part of the sacro-sciatic ligament and on the origin of the deep gluteus 

 muscle. It turns downward in the hollow between the trochanter major and the 

 tuber ischii over the gemellus, the tendon of the obturator internus, and the quad- 

 ratus femoris. In its descent in the thigh it lies between the biceps femoris ex- 

 ternally and the adductor, semimembranosus, and semitendinosus internally, and 

 it is continued between the two heads of the gastrocnemius as the tibial nerve. Its 

 chief branches are as follows: 



