862 THE NERVOUS SYSTEM. 



pierces the anterior layer, and, in company with the dorsal artery of the penis, 

 passes through the suspensory ligament, and, running forward, is distributed to 

 the glans. On the penis this nerve gives off a cutaneous branch which runs 

 along the side of the organ ; it is joined with branches of the sympathetic, and 

 supplies the integument of the upper surface and sides of the penis and prepuce, 

 giving a large branch to the corpus cavernosum. 



In the female the dorsal nerve is very small and supplies the clitoris. 



The Small Sciatic Nerve (Fig. 510) supplies the integument of the perinreum 

 and back part of the thigh and leg. It is usually formed by the union of three 

 branches, which arise from the first, second, and third nerves of the sacral plexus. 

 It issues from the pelvis through the great sacro-sciatic foramen below the Pyri- 

 formis muscle, descends beneath the Gluteus maximus with the sciatic artery, and 

 at the lower border of that muscle passes along the back part of the thigh, 

 beneath the fascia lata, to the lower part of the popliteal region, where it pierces 

 the fascia and becomes cutaneous. It then accompanies the external saphenous 

 vein to about the middle of the leg, its terminal filaments communicating with 

 the external saphenous nerve. 



The branches of the small sciatic nerve are all cutaneous, and are as follows : 

 perineal, femoral, and ascending. 



The perineal cutaneous branches are distributed to the skin at the upper and 

 inner side of the thigh, on its posterior aspect, and to the perineeum. One branch, 

 longer than the rest, the inferior pudendal, curves forward below the tuber ischii, 

 pierces the fascia lata, and passes forward beneath the superficial fascia of the 

 peringeum to be distributed to the integument of the scrotum in the male and the 

 labium in the female, communicating with the superficial perineal and inferior 

 haemorrhoidal nerves. 



The femoral cutaneous branches consist of filaments, which are derived from 

 both sides of the nerve and are distributed to the skin of the inner and outer side 

 of the thigh on its posterior aspect, as far down as the middle of that region, and 

 also to the skin of the back part of the thigh, popliteal region, and upper part 

 of the leg. 



The ascending cutaneous branches consist of two or three filaments, which turn 

 upward round the lower border of the gluteus maximus, to supply the integument 

 covering its surface (nervi clunium infer lores). 



The Great Sciatic Nerve (Fig. 510) supplies nearly the whole of the integu- 

 ments of the leg, the muscles of the back of the thigh, and those of the leg and 

 foot. It is the largest nervous cord in the body, measuring three-quarters of an 

 inch in breadth, and is the continuation of the lower cord of the sacral plexus. 

 It passes out of the pelvis through the great sacro-sciatic foramen, below the 

 Pyriformis muscle. It descends between the trochanter major and tuberosity of 

 the ischium, along the back part of the thigh to about its lower third, where it 

 divides into two large branches, the internal and external popliteal nerves. 



This division may take place at any point between the sacral plexus and the 

 lower third of the thigh. When the division occurs at the plexus, the two nerves 

 descend together, side by side ; or they may be separated at their commencement 

 by the interposition of part or the whole of the Pyriformis muscle. As the nerve 

 descends along the back of the thigh it rests at first upon the External rotator 

 muscles, in company with the small sciatic nerve and artery, being covered by 

 the Gluteus maximus ; lower down, it lies upon the Adductor magnus and is 

 covered by the long head of the Biceps. 



The branches of the nerve, before its division, are articular and muscular. 



The articular branches arise from the upper part of the nerve ; they supply 

 the hip-joint, perforating its fibrous capsule posteriorly. These branches are 

 sometimes derived from the sacral plexus. 



The muscular branches are distributed to the Flexors of the leg viz. the 

 Biceps, Semitendinosus, and Semimembranosus, and a branch to the Adductor 

 magnus. These branches are given off beneath the Biceps muscle. 



