The superior branch takes the course of tbe superficial trunk of the corresponding artery', courses along the convex border of the glutmus minimus, and supplies principally the upper and back part of the glutwus me dins. The inferior branch is directed down wards, forwards, and outwards between the two glutmi, and, after a short course, divides into a superficial branch, supplying the upper and anterior part of the glutxus mcdius ; and a deep branch running across the &Litmus minimus, supplying it and the medius, and terminating near the great trochanter, by entering the substance of the tensor vaa,in femoris, at the lower, inner, and back part of its sheath.
The inferior glutceal nerve (lesser sciatic) arises from the back part of the sacral plexus by one or more roots. It emerges from the pelvis at the lower and anterior part of the great sacro-sciatic notch, either as a single, or as two, or three, trunks, below the pyri formis, and about a quarter of an inch behind and internal to the great sciatic. It is directed between the tuberosity of the ischium, and the great trochanter, but nearer the former, 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 tmus 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 glutmal having emerged from beneath the lower border of the glutmus maximus, divides:into its two terminal branches, perimeal cutaneous, and cutaneous branch to the thigh and upper part of the leg. 7'lle peri meal cutaneous nerve is reflected upon the lower border of the glutmus 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 glutmal 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 tipper 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 perineum ; it anastomoses either with the superficial perinmal, or the external perinmal 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 glutmal 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 vvhich situation it anastomoses with the external cutaneous nerve of the lumbar plexus. The large intern41 branch
runs down a little to the inside of the median line of the thigh to the skin in the poplitmal 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 poplitmal region, others very small, accompanying and surround ing the external saphmna 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 glutmal 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 tlze genzelli and quadratus fe nzoris 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 rapsular 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-poplitmal), 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 fbot. 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 poplitmal space, where it divides into terminal branches, the peronmal 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 poplitmal space. In the upper part of its course the nerve is rather deeply seated, being covered over by the glutazus maximus, and having be hind and internal to it the branches of the inferior glutwal nerve. At the lower border of the tendon of the &litmus maximus it is crossed by the long head of the biceps, and in the remainder of its course is covered only by the fascia.