IV. THE MUSCLES OF THE FOOT

1. THE DORSAL MUSCLE OF THE FOOT

Extensor digitorum brevis Extensor hallucis brevis

The fascia on the dorsum of the foot (fascia dorsalis pedis) is a thin, membranous layer, continuous above with the inferior extensor retinaculum; at the sides of the foot it blends with the plantar aponeurosis; anteriorly it ensheathes the tendons on the dorsum of the foot.

The Extensor digitorum brevis (figs. 655, 662) is a thin muscle, which arises from the forepart of the upper and lateral surface of the calcaneum, in front of the groove for the Peroneus brevis; from the interosseous talocalcaneal ligament, and the stem of the inferior extensor retinaculum. It passes obliquely forwards and medially across the dorsum of the foot, and ends in four tendons. The medial part of the muscle is usually a more or less distinct slip ending in a tendon which crosses the dorsalis pedis artery and is inserted into the dorsal surface of the base of the proximal phalanx of the great toe; it is sometimes described as a separate muscle—the Extensor hallucis brevis. The other three tendons are inserted into the lateral sides of the tendons of the Extensor digitorum longus of the second, third and fourth toes.

Nerve-supply.-The Extensor digitorum brevis is supplied by the lateral terminal branch of the anterior tibial (deep peroneal) nerve (L. 4 and 5 and S. 1).

Actions.—The Extensor digitorum brevis extends the phalanges of the four toes into which it is inserted, but, in the great toe, acts only on the first phalanx.

Figure 662
Right ankle synovial sheaths of the tendons lateral view - Figure 662
2. THE PLANTAR MUSCLES OF THE FOOT

The plantar aponeurosis (fig. 664) is of great strength, and consists of white fibers disposed, for the most part, longitudinally : it is divided into central, lateral, and medial portions.

The central portion is the thickest: it is narrow behind, and attached to the medial tubercle of the calcaneum posterior to the origin of the Flexor digitorum brevis; it becomes broader and thinner in front, and divides near the heads of the metatarsal bones into five processes, one for each toe. Each of these processes splits opposite the metatarsophalangeal joint into a superficial and a deep stratum. The superficial stratum is inserted into the skin of the transverse sulcus which separates the toes from the sole. The deep stratum divides into two slips which embrace the sides of the flexor tendons of the toes, and blend with the fibrous sheaths of these tendons and with the deep transverse ligaments of the sole, thus forming a series of arches through which the tendons of the short and long flexors pass to the toes. Through the intervals between the five processes the digital vessels and nerves and the tendons of the Lumbrical muscles are transmitted. At the point of division of the aponeurosis numerous transverse fasciculi bind the processes together, and connect them with the skin. The central portion of the plantar aponeurosis is continuous with the lateral and medial portions, and sends upwards, at the lines of junction, two vertical intermuscular septa, which separate the intermediate from the lateral and medial groups of plantar muscles; from these vertical septa thinner transverse septa are derived which separate the different layers of muscles. The deep surface of the central part of the aponeurosis gives origin behind to the Flexor digitorum brevis.

The lateral portion covers the under surface of the Abductor digiti minimi; it is thin in front and thick behind where it forms a strong band between the lateral tubercle of the calcaneum and the base of the fifth metatarsal bone; it is continuous medially with the central portion, and laterally with the fascia on the dorsum of the foot.

Figure 664
Right foot plantar aponeurosis plantar view - Figure 664
The medial portion is thin, and covers the under surface of the Abductor hallucis; it is continuous behind with the flexor retinaculum (lacinate ligament); medially with the fascia, dorsalis pedis, and laterally with the central portion of the plantar aponeurosis.

The muscles in the plantar region of the foot may be divided into medial, lateral and intermediate groups; but for descriptive purposes it is more convenient to group theirs in four layers, as met with in the course of dissection.

The First Layer (fig. 665)

Abductor hallucis Flexor digitorum brevis Abductor digiti minimi

The Abductor hallucis (fig. 665) lies along the medial border of the foot and covers the origins of the plantar vessels and nerves. It arises from the medial tubercle of the calcaneum, the flexor retinaculum (laciniate ligament); the plantar aponeurosis, and the intermuscular septum between it and the Flexor digitorum brevis. The fibers end in a tendon which is inserted, together with the medial tendon of the Flexor hallucis brevis into the medial side of the base of the proximal phalanx of the Great toe.

Figure 665
Left foot muscles plantar view - Figure 665
Nerve-supply.–The Abductor hallucis is supplied by the medial plantar nerve (L. 5 and S. 1).

Actions.-The Abductor hallucis flexes and abducts the proximal phalanx of the great toe.

The Flexor digitorum brevis (fig. 665) is immediately above the central part of the plantar aponeurosis. Its deep surface is separated from the lateral plantar vessels and nerves by a thin layer of fascia. It arises by a narrow tendon from the medial tubercle of the calcaneum, from the central part of the plantar aponeurosis, and from the intermuscular septa between it and the adjacent muscles. It divides into four tendons, one for each of the four lesser toes. Opposite the bases of the proximal phalanges, each tendon divides into two slips, to allow of the passage of the corresponding tendon of the Flexor digitorum longus; the two slips then unite, partially decussate, and form a grooved channel for the reception of the tendon of the Flexor digitorum longus. The tendon divides again and is inserted into the sides of the middle phalanx about its middle. The mode of division of the tendons of the Flexor digitorum brevis, and of their insertion into the phalanges, is identical with that of the tendons of the Flexor digitorum sublimis in the hand.

Nerve-supply.-The Flexor digitorum brevis is supplied by the medial plantar nerve (L. 5 and S. 1 and 2).

Actions.—The Flexor digitorum brevis flexes the middle phalanges upon the proximal; continuing its action it flexes the proximal phalanges and brings the toes together.

The fibrous sheaths of the flexor tendons (fig. 663).—The terminal portions of the tendons of the long and short flexor muscles are contained in osseoaponenrotic canals similar in their arrangement to those in the fingers. These canals are bounded above by the phalanges, and below by fibrous bands which arch across the tendons and are attached on either side to the margins of the phalanges. Opposite the shafts of the proximal and middle phalanges the fibrous bands (vaginal ligaments) are strong, and the fibers are transverse; but opposite the joints they are much thinner, and the fibers are directed obliquely. Each canal contains a synovial sheath, which is reflected on the contained tendons; within this sheath vincula tendinum are arranged similarly to those of the fingers.

The Abductor digiti minimi (fig. 665) lies along the lateral border of the foot, and its medial margin is in relation with the lateral plantar vessels and nerve. It arises from the lateral and medial tubercles of the calcaneum, from the under surface of the bone between the processes, from the plantar aponeurosis, and from the intermuscular septum between it and the Flexor digitorum brevis. Its tendon glides over a smooth facet on the under surface of the base of the fifth metatarsal bone and is inserted, with the Flexor digiti minimi brevis, into the lateral side of the base of the proximal phalanx of the fifth toe.

Nerve-supply.-The Abductor digiti minimi is supplied by the lateral plantar nerve (S. 1 and 2).

Actions.-The Abductor digiti minimi flexes and abducts the proximal phalanx of the little toe.

The Second Layer (figs. 666, 667)

Flexor digitorum accessorius (Quadrates plantae) Lumbricales

The Flexor digitorum accessorius (Quadrates plantae) (fig. 667) arises by two heads, which are separated from each other by the long plantar ligament; the medial, and larger head is muscular, and is attached to the medial concave surface of the calcaneum below the groove for the tendon of the Flexor hallucis longus; the lateral head, flat and tendinous, arises from the calcaneum in front of the lateral tubercle and from the long plantar ligament. The two portions join at an acute angle and end in a flattened band which is inserted into the superior surface and lateral margin of the tendon of the Flexor digitorum longus, forming a kind of groove in which the tendon is lodged. It usually sends slips to those tendons of the Flexor digitorum longus which pass to the second, third and fourth toes.

Nerve-supply.-The Flexor digitorum accessorius is supplied by the lateral plantar nerve (S. 1)

Actions.-The Flexor digitorum accessorius assists the Flexor digitorum longus and converts the oblique pull of the tendons of that muscle into a direct backward pull on the toes.

The Lumbricales (fig. 667) are four small muscles, accessory to the tendons of the Flexor digitorum longus, and numbered from the medial side of the foot; they arise from these tendons, as far back as their angles of separation, and, with the exception of the first, which arises only from the medial border of the first tendon of the Flexor digitorum longus, each springs from two tendons. The muscles end in tendons which pass forwards and upwards on the medial sides of the four lesser toes, and are inserted into the expansions of the tendons of the Extensor digitorum longus on the dorsal surfaces of the proximal phalanges.

Nerve-supply.-The first Lumbrical is supplied by the medial plantar nerve (L. 5 and S .1); the others by the deep branch of the lateral plantar nerve (S. 1 and 2).

Actions.-The Lumbricals flex the proximal phalanges and, by their insertions into the tendons of the Extensor digitorum longus, extend the middle and distal phalanges.

The Third Layer (figs, 666, 668)

Flexor hallucis brevis Adductor hallucis Flexor digiti minimi brevis

The Flexor hallucis brevis (fig. 668) arises by a pointed, tendinous process from the medial part of the under surface of the cuboid bone, behind the groove for the Peroneus longus tendon; from the contiguous portion of the lateral cuneiform bone, and from the part of the tendon of the Tibialis posterior which is attached to that bone. It divides into a medial and a lateral portion, and the tendons of these are inserted into the corresponding sides of the base of the proximal phalanx of the great toe, a sesamoid bone being present in each tendon at its insertion. The medial portion is blended with the Abductor hallucis previous to its insertion; the lateral, with the Adductor hallucis. The lateral portion of the Flexor hallucis brevis is sometimes described as the first plantar interosseous muscle.

Figure 666
Right foot muscles and nerve supply plantar view - Figure 666
Nerve-supply.–The Flexor hallucis brevis is supplied by the medial plantar nerve (L. 5 and S. 1).

Action.-The Flexor hallucis brevis flexes the proximal phalanx of the great toe.

The Adductor hallucis (fig. 668) arises by two heads-oblique and transverse. The oblique head, springs from the bases of the second, third and fourth metatarsal bones, and from the sheath of the tendon of the Peroneus longus and is, inserted, together with the lateral portion of the Flexor hallucis brevis, into the lateral side of the base of the proximal phalanx of the great toe. The transverse head, a narrow, flat fasciculus, arises from the plantar metatarsophalangeal ligaments of the third, fourth and fifth toes (sometimes only from the third and fourth), and from the deep transverse ligaments of the sole. It is inserted into the lateral side of the base of the proximal phalanx of the great toe, its tendon of insertion blending with that of the oblique head.

Figure 667
Left foot muscles and flexor digitorum longus and flexor hallucis longus tendons plantar view - Figure 667
Figure 668
Left foot muscles deep - Figure 668
Nerve-supply.—The Adductor hallucis is supplied by the deep branch of the lateral plantar nerve (S. 1. and 2).

Actions.-The oblique head of the Adductor hallucis is chiefly concerned in adducting, but it also assists in flexing, the great toe; the transverse head approximates the toes and thus increases the curve of the transverse arch of the metatarsus, The Flexor digiti minimi brevis (fig. 668) arises from the medial part of the plantar surface of the base of the fifth metatarsal bone, and from the sheath of the Peroneus longus; its tendon is inserted into the lateral side of the base of the proximal phalanx of the fifth toe. Occasionally a few of the deeper fibers are inserted into the lateral part of the distal one-half of the fifth metatarsal bone; these are described by some as a distinct muscle–the opponens digiti minimi.

Nerve-supply.—The Flexor digiti minimi brevis is supplied by the superficial branch of the lateral plantar nerve (S.1 and 2).

Action.——The Flexor digiti minimi brevis flexes the little toe.

The Fourth Layer

Interossei.

The Interossei in the foot are similar to those in the hand; but are grouped on each side of the middle line of the second digit instead of that of the third. They consist of a dorsal and a plantar set.

The Interossei dorsales (fig. 669), four in number, are situated between the metatarsal bones. They are bipennate muscles, each arising by two heads from the adjacent sides of the metatarsal bones between which it is placed; their tendons are inserted into the bases of the proximal phalanges, and into the aponeuroses of the tendons of the Extensor digitorum longus. The first is inserted into the medial side of the second toe; the other three into the lateral sides of the second, third, and fourth toes, in the angular interval between the heads of each of the three lateral .muscles, one of the perforating arteries passes to the dorsum of the foot; through the space between the heads of the first muscle the terminal part of the dorsalis pedis artery enters the sole of the foot.

Figure 669
Dorsal interossei of the foot - Figure 669
Figure 670
Planttar interossei of the foot - Figure 670
The Interossei plantares (fig. 670), three in number, lie below rather than between the metatarsal bones, and each is connected with but one metatarsal bone. They arise from. the bases and medial sides of the shafts of the third, fourth, and fifth metatarsal bones, and are inserted into the medial sides of the bases of the proximal phalanges of the same toes, and into the aponeuroses of the tendons of the Extensor digitorum longus.

Nerve-supply.-The Dorsal and Plantar interossei are supplied by the deep branch of the lateral plantar nerve (S. 1 and, 2), except those in the fourth interosseous space, which are supplied by the superficial branch of the same nerve. The first Dorsal interosseous frequently receives an extra filament from the medial branch of the anterior tibial nerve on the dorsum of the foot, and the second Dorsal interosseous a twig from the lateral branch of the same nerve.

Actions.-The Dorsal interossei are abductors from an imaginary line passing through the axis of the second toe, so that the first muscle draws the second toe medially, the second muscle draws the same toe laterally, and the third and fourth draw the third and fourth toe laterally. They assist in flexing the proximal and extending the middle and distal phalanges. The Plantar interossei adduct the third, fourth and fifth toes towards the imaginary line passing through the second toe; and, by means of their insertions into the aponeuroses of the Extensor tendons, assist in flexing the proximal phalanges and extending the middle and distal phalanges.

 


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