One of the terminal branches of the great sciatic nerve, from the upper part of the popliteal space to the lower border of the popliteus muscle, where it is continued down the leg. It lies at first beneath semimembranosus; then, crossing the popliteal vessels to their inner side, it lies on popliteus and is covered by gastrocnemius and plantaris. It then passes down the back of the leg between the superficial and deep muscles with the posterior tibial vessels, at first on their inner side, but crossing over in the middle of the leg the nerve lies on their outer side in the lower half. It divides into its terminal branches, the internal and external plantar nerves, beneath the internal annular ligament.

Branches

In the popliteal space:

Muscular to gastrocnemius, plantaris, soleus, and popliteus.

The latter nerve winds round the lower border of the muscle and enters its deep surface, giving off a branch to tibialis posticus.

Articular

Several to knee-joint, and one to the upper tibiofibular joint, and to tarsal and metatarsal joints through the short saphenous nerve.

Cutaneous

The tibial communicating, pierces the deep fascia in the middle third of the leg, where it is joined by the peroneal communicating, to form the short saphenous nerve which supplies the skin on the back of the leg, and, passing behind the external malleolus, supplies the ankle and heel and outer side of the foot and little toe.

In the back of the leg:

Muscular to soleus, tibialis posticus, flexor longus hallucis and flexor longus digitorum.

Cutaneous to the skin of the heel and the posterior part of the sole of the foot by a branch called the internal calcanean.

Internal Plantar Nerve

A terminal branch of the posterior tibial nerve arises beneath the internal annular ligament, and passes forwards between abductor hallucis and flexor brevis digitorum with the internal plantar artery.

Branches

Muscular to abductor hallucis, flexor brevis digitorum, flexor brevis hallucis, and first lumbrical. Articular to inner tarsal and metatarsal joints. Cutaneous to the inner half of the sole of the foot and the three and a half toes on the inner side.