SPINAL NERVES. 



767 



over the back and inner part of the gemelli, 

 and divides into muscular and cutaneous 

 branches. The muscular branches are long and 

 numerous, being destined to supply the glu- 

 taeus maximus. One series are directed out- 

 wards, upwards, and forwards, and, entering 

 its anterior surface, ramify through the sub- 

 stance of the muscle, as far as its upper and 

 anterior part. The other series are directed 

 downwards, backwards, and outwards, over 

 the tuberosity of the ischium, and supply the 

 lower and back part of the muscle. 



The inferior glutaeal having emerged from 

 beneath the lower border of the glutaeus 

 maximus, divides'into its two terminal branches, 

 perinceal cutaneous, and cutaneous branch to 

 the thigh and upper part of the leg. The peri- 

 nceal cutaneous nerve is reflected upon the 

 lower border of the glutasus maximus, and 

 describes a curve, the concavity of which 

 looks towards the sacrum. It soon divides 

 into an external large branch, supplying the 

 skin in the glutaeal region, and an internal 

 small branch (the long inferior pudendal of 

 Scemmering), which passes in a curved man- 

 ner beneath the tuberosity of the ischium. It 

 is then directed beneath the fascia of the 

 upper and inner part of the thigh, running 

 parallel to the ascending ramus of the ischium, 

 and at or near the junction of the latter with 

 the descending ramus of the pubis, perforates 

 the fascia, and becomes cutaneous, supplying 

 the skin in the perinaeum ; it anastomoses 

 either with the superficial perinseal, or the 

 external perineeal nerve, and sends terminal 

 branches to supply the inner and outer por- 

 tions of the scrotum, and the lower part of 

 the skin of the penis. 



The cutaneous branch to the back of the thigh 

 and upper part of the leg. The continuation 

 of the trunk of the inferior glutasal is situated 

 anterior and external to the above-named 

 branches. It passes obliquely over the inner 

 and back part of the biceps muscles, and, a 

 little above the middle of the thigh, ordinarily 

 divides into two branches. The small external 

 branch passes downwards, forwards, and out- 

 wards to the upper part of the lower third of 

 the thigh, in which situation it anastomoses 

 with the external cutaneous nerve of the 

 lumbar plexus. The large intern*! branch 

 runs down a little to the inside of the median 

 line of the thigh to the skin in the poplitaeal 

 region, where it divides into external terminal 

 filaments, supplying the skin over the outer 

 and back part of the tibia and fibula, and in- 

 ternal filaments, some of which go to the skin 

 at the inner part of the poplitaeal region, 

 others very small, accompanying and surround- 

 ing the external saphaena vein, communicate 

 below the middle of the leg with filaments 

 given off from the external saphasnus nerve. 



The nerve for the pyriformis passes below 

 the level of the superior glutreal nerve, from 

 the middle of the back part of the plexus, 

 generally taking its origin from the third sa- 

 cral nerve. It is distributed to the anterior 

 surface of the muscle. 



The nerves for the gemelli and quadratus fe- 



moris pass from the plexus along the lower 

 part of the pyriformis, close to the os inno- 

 minatum, to the anterior surface of the muscles. 

 That for the quadratus femoris gives off a 

 few branches to the napsular ligament, one 

 of which enters the articulation, and usually 

 sends off the nerve which supplies the inferior 

 gemellus. This nerve comes off frequently 

 from the upper part of the great sciatic. 



The great sciatic nerve (the sciatic, ischi- 

 atic, femoro-poplitasal), the largest nerve in 

 the body, is formed by the convergence of a 

 branch of the fourth lumbar, the lumbo-sa- 

 cral, and the three or four upper sacral 

 nerves ; represents the termination of the sa- 

 cral plexus, and is destined to supply the 

 muscles at the back part of the thigh, and the 

 muscles and integuments of the leg and foot. 

 It escapes from the pelvis, from beneath the 

 lower border of the pyriformis, as a flattened 

 ribbon-shaped nerve, about half an inch broad, 

 soon becomes rounded, and- continuing its 

 course from between the great trochanter 

 and tuberosity of the ischium, descends with 

 a slight inclination outwards to the back part 

 of the thigh, a little to the outside of the me- 

 dian line, as far as, or somewhat above, the 

 level of the upper angle of the poplitaeal space, 

 where it divides into terminal branches, the 

 peronaeal and posterior tibial. This division 

 occasionally takes place within the pelvis, in 

 which instances the outer division passes 

 either between the lower fascicles of the 

 pyriformis or above the muscle, the inner 

 beneath the lower edge of the muscle. In 

 some instances it takes place while the nerve 

 is placed between the trochanter and tube- 

 rosity: in others, again, the two trunks are dis- 

 tinct as far as this situation, where they again 

 unite, and subsequently divide in the popliteal 

 space. In the upper part of its course the 

 nerve is rather deeply seated, being covered 

 over by the glutaeus maximus, and having be- 

 hind and internal to it the branches of the 

 inferior glutasal nerve. At the lower border 

 of the tendon of the glutaeus maximus it is 

 crossed by the long head of the biceps, and in 

 the remainder of its course is covered only 

 by the fascia. 



It is in relation in front with the two ge- 

 melli and obturator internus, the quadratus 

 femoris and adductor magnus. Behind these 

 muscles it passes successively from above 

 downwards, is in close contact with the su- 

 perior, and separated from the adductor 

 magnus by a quantity of fat and cellular 

 membrane. The branches given off from the 

 sciatic nerve are muscular and articular. The 

 muscular branches come away above the 

 middle of the thigh, with the occasional ex- 

 ception of that for the short head of the biceps, 

 which arises near the middle. 



There are several branches for the long head 

 of the biceps, some of which ascend to be dis- 

 tributed to the muscle at its origin; others 

 descend for some distance, and enter its an- 

 terior surface. 



The nerve for the semi~tendinous is a long 

 delicate filament, which usually passes down 



