The great sciatic nerve now divides in the popliteal space into the peroneus communis (d) and the tibialis (e).

[Fig. 163].—Dissection of Leg, Lateral View, to show Distribution of the Great Sciatic Nerve.

The biceps, caudofemoralis, gluteus maximus, gluteus medius, tensor vaginæ femoris, and part of the peroneus longus have been removed. a, N. ischiadicus or great sciatic nerve; b, muscular branch; c, N. suralis; d, N. peroneus communis; e, N. tibialis; f, N. peroneus profundus; g, N. peroneus superficialis and its terminal branches; h, branches of N. cutaneus femoris posterior; i, N. gluteus inferior; j, N. gluteus superior; k, vena saphena parva; k′, communicating branch to V. glutea inferior. 1, M. sartorius; 2, cut origin of M. gluteus medius; 3, cut origin of M. gluteus maximus; 4, cut origin of M. caudofemoralis; 5, M. gluteus minimus; 6, M. gemellus superior; 7, M. pyriformis; 8, M. flexor caudæ longus; 9, M. obturator internus; 10, M. quadratus femoris; 11, tuberosity of the ischium; 12, great trochanter of femur; 13, M. rectus femoris; 14, M. vastus lateralis; 15, M. adductor femoris; 16, M. semimembranosus; 17, M. semitendinosus (the slender ribbon-like muscle crossing this is M. tenuissimus); 18, M. vastus intermedius; 19, M. plantaris; 20, M. gastrocnemius; 21, M. peroneus longus (cut); 22, M. tibialis anterior; 23, M. extensor longus digitorum; 24, transverse ligament; 25, M. peroneus brevis; 26, M. soleus; 27, tendon of Achilles; 28, M. extensor brevis digitorum; 29, tendon of M. peroneus tertius.

a. N. peroneus communis (d).—This is the more lateral of the two divisions of the great sciatic nerve. It passes along the medial surface of the biceps to the lateral surface of the lateral head of M. gastrocnemius (20), where it extends to a point just distad of the head of the fibula. Here it passes beneath that part of the gastrocnemius which has origin on the fascia of the shank, passes between the soleus and peroneus longus (21), then between the peroneus longus and peroneus tertius. It gives off a number of small muscular branches, then divides two or three centimeters distad of the head of the fibula into two main branches, N. peroneus superficialis (g) and N. peroneus profundus (f).

(1) N. peroneus superficialis (g).—The superficial peroneal nerve passes distad between the peroneus longus and peroneus tertius. Near the ankle it becomes superficial, passing along the concavity of the ankle across the transverse ligament which binds down the tendons of the extensor longus (23) and tibialis anterior (22), and thus reaches the dorsal side of the foot. Two or three minute twigs are given off to the ankle, then the nerve divides into four divisions. These pass distad to the toes, subdividing so as to send a nerve to each side of each toe.

(2) N. peroneus profundus (f).—The deep peroneal nerve passes between the tibialis anterior and extensor longus digitorum muscles, gives branches to these muscles, and passes distad with the tibialis anterior artery, lying on the inner surface of the tibialis anterior muscle. It passes onto the dorsum of the foot, lying on the inner surface of the tendon of the muscle. On the tarsus it divides into two branches. The lateral branch passes into the extensor brevis digitorum, while the medial one extends in the dorsal groove between metatarsals four and five to the toes; here it divides into two nerves which supply the contiguous sides of digits four and five.

b. N. tibialis (e).—The tibial nerve passes distad parallel with the peroneal nerve, but mediad of it. It passes between the lateral and medial heads of the gastrocnemius, giving off muscular branches to these, and to the plantaris and soleus. It then passes between the plantaris and the medial head of the gastrocnemius, and reaches the space between the plantaris and flexor longus hallucis, where it passes distad. It gives off, in the region just described, muscular branches to the flexor longus digitorum, flexor longus hallucis, and tibialis posterior. Below the middle of the lower leg the nerve becomes superficial ([Fig. 127], i, [page 310]), lying on the ventral surface of the flexor longus hallucis. It passes in the depression between the heel and the medial malleolus onto the plantar surface of the tarsus, sends a small branch to the plantar surface of the heel, and divides into two branches, the medial and the lateral plantar nerves.

(1) N. plantaris medialis.—The medial plantar nerve passes along the medial border of the flexor brevis digitorum and divides into two branches. One passes to the medial (second) digit, supplying both sides; the other supplies the third digit in the same way. Both send branches to the fibrous pad on the sole of the foot.

(2) N. plantaris lateralis.—The lateral plantar nerve passes laterad across the tendon of the flexor longus digitorum to its lateral edge. At about the proximal end of the metatarsi it divides into two branches. The lateral branch passes distad to the ventral surface of the fifth digit. The medial branch passes beneath the tendon of the flexor longus digitorum and transversely across the interossei; it divides into numerous tendons which innervate the interossei and other short muscles of the sole of the foot.