326 



THE SPINAL NERVES. 



vessels through the great sacro-sciatic foramen above the pyriformis muscle, and 

 immediately divides into two branches, which run forwards between the glutens 

 medius and minimus, supplying those muscles and the tensor vaginas femoris. 



(a) The upper branch is the smaller and more superficial ; it sends its offsets 

 solely to the glutens medius. 



(b) The lower branch crosses the middle of the gluteus minimus muscle with the 

 lower branch of the gluteal artery ; it sends branches to both the gluteus medius 

 and minimus, and generally perforates the fore part of the latter muscle to reach the 

 deep surface of the tensor vaginas femoris, in which it ends. 



Varieties. The superior gluteal sometimes receives fibres also from the second sacral 

 nerve. A branch to the pyriformis muscle may be given off from the lowest root of this 

 nerve. 



Fig. 211. BRANCHES OF THE SACRAL PLEXUS IN THE 

 BUTTOCK. (Hirschfeld and Leveille.) i 



a, great trochanter ; i, tensor vaginne femoris 

 muscle ; c, tendon of the obturator interims muscle ; 

 d, upper part of the vastus externus ; e, coccyx ; 

 /, gracilis muscle; between/and d r the adductor magnus, 

 semitendinosus, and biceps muscles, with the lower 

 end of the gluteus maximus ; 1, 1. upper branch of the 

 superior gluteal nerve ; 1', 1', inferior branch of the 

 same nerve ; 1", branch of the nerve to the tensor 

 vaginae femoris ; 2, 2, sacral plexus and great sciatic 

 nerve ; 2', muscular twig from the plexus to the pyri- 

 formis ; 2" branch to the gemellus superior and obturator 

 internus; 3, small sciatic nerve, 3', 3', placed on the upper 

 and lower parts of the divided gluteus maximus, the 

 branches of the inferior gluteal nerve ; 3", the gluteal 

 cutaneous branches of the small sciatic nerve winding 

 round the lower border of the gluteus maximus ; 4, the 

 continuation of the small sciatic nerve as posterior 

 cutaneous nerve of the thigh ; 4', inferior pudendal 

 branch of the small sciatic ; 5, placed on the lower 

 part of the sacral plexus points to the origin of the pndic 

 nerve ; 6, its pei^neal division with its muscular 

 branches ; 6', internal superficial perineal branch ; 

 6", external superficial perineal ; -t- +, distribution of 

 these nerves and the inferior pudendal on the scrotum ; 

 7, dorsal nerve of the penis. 



Inferior gluteal nerve. The inferior gluteal nerve arises from the back of 

 the plexus, being formed of fibres which are derived from the lumbo-sacral cord, the 

 first and second sacral nerves. It usually sends a branch downwards to join the 

 commencement of the small sciatic nerve, and sometimes the two nerves are more 

 closely connected at their origins. The inferior gluteal nferve turns backwards at the 

 lower border of the pyriformis muscle, and immediately divides into a number of 

 branches which, diverging upwards and downwards, enter the deep surface of the 

 gluteus maximus muscle about midway between its origin and insertion. 



Small sciatic nerve. The small sciatic nerve (nervus cutaneus femoris 

 posterior) is entirely a sensory nerve, supplying the integument of the lower part of 

 the buttock, the back of the thigh, and the upper part of the back of the leg ; it also 

 furnishes one branch to the perineum the inferior pudendal nerve. 



The nerve takes its origin usually from the back of the upper three sacral nerves 

 by as many roots, the highest of which arises in common with a part of the inferior 

 gluteal nerve. Emerging below the -pyriformis muscle, it descends beneath the 

 gluteus maximus muscle, resting on the great sciatic nerve, and then along the back 

 of the thigh under cover of the fascia lata to a little beyond the knee. Here it 

 becomes subcutaneous, and its terminal ramifications are distributed to the skin of 



