3. Remove the rest of the deep fascia from the medial and lateral sides of the foot and note the first layer of muscles comprising the abductor hallucis, flexor digitorum brevis and abductor digiti minimi from medial to lateral. Note the origin of these muscles from the calcaneal tuberosity. Trace them towards their insertions. The abductor hallucis is inserted into the medial side of the base of the proximal phalanx of the first toe. The abductor digiti minimi is inserted into the lateral side of the base of the proximal phalanx of the fifth toe. The flexor digitorum brevis splits into four slips which are inserted into the sides of the middle phalanges of the lateral four toes. Note that these tendons are covered by fibrous flexor sheaths over the digits.

4. Secure the medial plantar nerve and artery between the abductor hallucis and flexor digitorum brevis. Note that the nerve supplies cutaneous branches to the medial three and a half toes and motor branches to:

(a)flexor digitorum brevis;

(b) abductor hallucis;

(c) flexor hallucis brevis; and

(d) the first lumbrical. The medial plantar artery communicates with branches of the plantar arterial arch (see later).

5. Cut the abductor hallucis near its origin and turn it forwards to expose the commencement of the medial and lateral plantar nerves and arteries which are the terminal branches of the tibial nerve and posterior tibial artery.

6. Detach the flexor digitorum brevis from its origin and reflect it forwards, and trace the lateral plantar nerve and artery towards the lateral side of the foot.

7. Note that the lateral plantar nerve supplies cutaneous branches to the lateral one and a half toes and muscular branches to the abductor digiti minimi and the remaining plantar muscles that are not supplied by the medial plantar nerve. Second layer

8. Cut the abductor digiti minimi at its origin and reflect it. You will now see the second layer which consists of the tendons of flexor hallucis longus; flexor digitorum longus and the muscles associated with it, i.e. quadratus plantae and the four lumbricals.

9. Trace the long flexor tendons to the toes by splitting the fibrous flexor sheaths covering them longitudinally.

10. Find the tendon of the flexor hallucis longus in the groove of the sustentaculum tali of the calcaneus and trace it forwards to its insertion into the base of the distal phalanx of the first toe.

1. Observe that the tendons of the flexor digitorum brevis lie superficial to the tendons of the flexor digitorum longus and that both sets of tendons are inserted into the lateral four toes. Note that the brevis tendons split to pass to the sides of the middle phalanges and the longus tendons pass between the split parts to the bases of the distal phalanges.

2. Note that the lumbricals, which arise from the tendons of the flexor digitorum longus, insert into the tibial side of the extensor expansion.

3. Clean the two heads of origin of the quadratus plantae which arise from the medial and lateral edges of the calcaneus, and observe its insertion into the tendon of the flexor digitorum longus.

4. Divide the two heads of the quadratus plantae and the tendons of the long flexors near the heel and turn them distally to expose the third layer of muscles. These are, from medial to lateral:

(a)flexor hallucis brevis;

(b) adductor hallucis; and

(c) flexor digiti minimi brevis.

5. Clean the flexor hallucis brevis and cut it near its origin from the cuboid bone. Note that it divides into two slips; the medial slip joins the abductor hallucis tendon while the lateral one joins the adductor hallucis to be inserted into the respective sides of the proximal phalanx of the first toe. Note the sesamoid bones at these insertions. Clean the oblique and transverse heads of the adductor hallucis. Note the origin of the oblique head from the bases of the second, third and fourth metatarsal bones and that of the transverse head from the capsules of the lateral four metatarsophalangeal joints. Note the origin of the flexor digiti minimi brevis from the base of the fifth metatarsal bone and trace it to its common insertion with the abductor digiti minimi into the lateral side of the proximal phalanx of the fifth toe. Remove the third layer of muscles, taking care not to damage the lateral plantar nerve and artery.

6. Clean:

(a)the lateral plantar nerve and note that it supplies all the interossei of the four intermetatarsal spaces; and

(b) the lateral plantar artery forming the plantar arterial arch, which gives off the plantar metatarsal arteries terminating in plantar digital arteries. Note that the arch is reinforced by the dorsalis pedis artery entering the sole through the first intermetatarsal space.

7. Now clean the fourth layer comprising the interossei (three plantar and four dorsal) and the tendons of the tibialis posterior and fibularis longus. The three plantar interossei originate from the medial sides of the 3rd, 4th and 5th metatarsals, and the dorsal interossei originate from the adjacent sides of the metatarsals between which they lie. All the interossei insert into the bases of the proximal phalanges. Identify and clean the deep transverse metatarsal ligaments that connect the capsules of all five metatarsal joints. Note again that the lumbricals join the extensor expansions. Note as well that the axial line of the foot passes through the second toe (c.f. hand).

8. Identify the tendon of the tibialis posterior and trace its main insertion into the tuberosity of the navicular bone. Other slips pass from this tendon to the bases of the middle three metatarsal bones and to all the tarsal bones except the talus. Note that a slip passes backwards and blends with the plantar calcaneonavicular (spring) ligament.

9. Turn to the lateral side of the foot and confirm the insertion of the fibularis brevis into the lateral side of the base of the fifth metatarsal bone. Trace the fibularis longus tendon lying in a groove on the inferior surface of the cuboid bone to its insertion into the lateral side of the medial cuneiform and base of the first metatarsal bone.

20. Identify the long plantar ligament passing from the plantar aspect of the calcaneus to the lips of the groove lodging the fibularis longus tendon and to the bases of the lateral three metatarsals. The other deep ligaments will be examined later.

Summary

The plantar muscles of the foot appear to be sandwiched between the deep ligaments of the foot and the superficially placed plantar aponeurosis. Although the muscles of the foot are described in four layers, the arrangement is very much the same as in the hand since the muscles of the first and fifth toes correspond somewhat to those of the thumb and little finger.

The muscles on the lateral side show ligamentous degeneration while those on the medial side of the foot are better developed. This is to be correlated with differences in the functional adaptations of the foot in weight bearing and walking. The shifting of the axial line towards the second toe is also an expression of these functional adaptations. Further confirmation of this is evidenced by the fact that the first toe is placed in the same plane as the other toes and is also intimately connected with the second toe by the deep transverse metatarsal ligament. The medial plantar nerve corresponds more or less to the median nerve of the hand, while the lateral plantar nerve has similarities with the ulnar nerve in its distribution. The medial plantar nerve supplies the abductor and flexor muscles of the first toe, as well as the flexor digitorum brevis and the first lumbrical. All the other muscles of the foot are innervated by the lateral plantar nerve. The lateral plantar artery accompanied by the lateral plantar nerve runs between the first and second layers of muscles towards the lateral side of the foot and subsequently pursues a recurrent course medially between the third and fourth layers of muscles of the foot. This artery contributes to the plantar arterial arch.