The anterior crural nerve arises from the lumbar plexus, and enters the thigh behind Poupart's ligament between the psoas and iliacus muscles. It divides into an anterior and posterior portion, from which numbers of cutaneous and muscular branches spread over the front of the thigh.

The long saphenous nerve is the longest branch of the anterior crural. It goes down the thigh with the femoral vessels, and in the leg accompanies the long saphenous vein. It ends on the inner side of the foot.

The obturator nerve, also a branch of the lumbar plexus, divides into an anterior and posterior portion before it leaves the pelvis by the obturator foramen The anterior division proceeds down on the anterior surface of the adductor brevis muscle. The posterior division goes down between the adductor brevis and adductor magnus.

The great sciatic nerve is the largest branch of the sacral plexus, and the largest nerve in the body. It issues from the pelvis through the lower part of the great sacro-sciatic foramen, under the pyriformis muscle, about midway between the great trochanter and the tuberosity of the ischium. It passes down the middle of the back of the thigh on the adductor magnus muscle. It is at first superficial, but soon passes under the long head of the biceps muscle. About two-thirds down the thigh it divides into the internal and external popliteal nerves.

The internal popliteal nerve is the direct continuation of the great sciatic ; it becomes superficial as it emerges from under the biceps, and goes down the middle of the popliteal space to its lower border.

The posterior tibial nerve is the continuation of the internal popliteal ; it passes down the middle of the calf under the soleus muscle ; towards the ankle it inclines inwards, and between the heel and the inner ankle-bone it divides into the internal and external plantar nerves.

The plantar nerves go to the sole of the foot and toes.

Thus the sciatic nerve and its continuations form an almost direct line from the pelvis to the foot. They are closely associated with arteries of the same names and their accompanying veins.

The external popliteal nerve, the smaller division of the great sciatic, proceeds down the outer border of the popliteal space, along the inner side of the biceps. It turns round the head of the fibula, and divides into the musculo-cutaneous and anterior tibial.

The musculo-cutaneous nerve goes down the outside of the leg in the substance of the peroneous longus muscle ; about two-thirds down it becomes cutaneous, inclines forward, passes in front of the outer ankle, and divides into an internal and external branch, which pass to the dorsum of the foot and toes.

The anterior tibial nerve goes down the front of the leg, beneath the extensor longus digitorum muscle ; at the ankle it divides into an internal and external branch, which continue to the dorsum of the foot and toes. The great sciatic supplies nearly all the muscles of the back of the thigh, and all the muscles of the foot and leg (see table).

The lesser sciatic nerve arises from the same plexus, and issues from the pelvis in the same way as the greater sciatic. It is superficial in all its length. At the lower border of the popliteal space it pierces the fascia, and gives twigs to the skin of the upper part of the calf. In the gluteal region it gives recurrent branches to the skin of the buttocks.

The popliteal space is a lozenge-shaped space at the back of the knee—it is the ham. It contains the popliteal artery and vein with their branches, the two popliteal nerves, lesser sciatic, a branch of the obturator, and some small lymphatic glands. Above, and to the outer side, is the biceps muscle ; above, and to the inner side, are the semimembranosus and semitendinosus muscles ; the heads of the gastrocnemius and the plantaris muscle are below. The deep fascia is thin, but strong ; it is continuous with the fascia lata of the thigh.