THE FASCIÆ AND MUSCLES OF THE LEG

AND FOOT.

FASCIÆ.

The superficial fascia of the leg and foot presents no special features except in the sole, where it is greatly thickened by pads of fat, particularly under the tuberosity of the calcaneus, and under the balls of the toes.

The deep fascia has numerous important attachments about the knee. Posteriorly it forms the popliteal fascia, and is joined by expansions from the tendons of the sartorius, gracilis, semitendinosus, and biceps femoris muscles. In front of the knee it is attached to the patella, the ligamentum patella, and the tubercle of the tibia; medially and laterally it is connected to the condyles of the tibia and the head of the fibula, and helps to form the collateral patellar ligaments-broad fascial bands which pass obliquely from the sides of the patella to the condyles of the tibia, and are joined by fibres of the vasti muscles. Passing into the leg, the fascia blends, over the medial surface of the tibia, with the periosteum of the bone. It extends round the lateral side of the leg from the anterior crest to the medial border of the tibia, binding together and giving origin to the muscles, and gaining an attachment to the distal part of the body of the fibula. Two septa pass from its deep surface; one septum (anterior peroneal septum), attached to the anterior crest of the fibula, encloses the superficial peroneal nerve, and separates the extensor from the peronæi muscles. The other septum (posterior peroneal septum) is attached to the lateral crest of the fibula, and separates the peronæi from the flexor muscles. From the last-named septum another extends across the back of the leg; it forms a partition between the superficial and deep flexor muscles, and encloses the posterior tibial vessels and the tibial nerve. It gives rise to subordinate septa attached to the vertical line of the tibia and the medial crest of the fibula, which separate the tibialis posterior from the flexors of the toes on either side.

At the ankle the deep fascia is strengthened by additional transverse fibres, which give rise to thickened bands named the ligamentum laciniatum, lig. transversum cruris, lig. cruciatum cruris and the retinaculum of the peroneal muscles. They were formerly known as the annular ligaments.

The ligamentum laciniatum (O.T. internal annular ligament) stretches between the medial malleolus and the tuberosity of the calcaneus. While it is continuous, at its proximal border, with the general investment of the deep fascia, it is chiefly formed by the septal layer covering the deep muscles on the back of the leg. It sometimes gives insertion to the plantaris muscle. It is continuous, distally, with the plantar aponeurosis, and gives origin to the abductor hallucis muscle. It is pierced by the calcanean vessels and nerve. Along with the posterior tibial vessels and the tibial nerve, the tendons of the tibialis posterior, flexor digitorum longus, and flexor hallucis longus, pass beneath it, each enclosed in a separate mucous sheath.

The superior peroneal retinaculum (O.T. external annular ligament) is a thickened band of the deep fascia stretching between the lateral malleolus and the calcaneus. It binds down the tendons of the peronæi, which occupy a space beneath the ligament, lined by a single mucous sheath; while the inferior

peroneal retinaculum binds them down separately on the lateral surfaces of the calcaneus.

The ligamentum transversum cruris (O.T. anterior annular ligament, upper band), broad and undefined at its proximal and distal borders, stretches across the front of the ankle between the two malleoli. This band binds down, to the distal end of the tibia, the tendons of the tibialis anterior and extensor muscles of the toes. One mucous sheath is found deep to it, surrounding the tendon of the tibialis anterior.

Ligamentum Cruciatum Cruris. On the dorsum of the foot, where the general covering of deep fascia is much thinner, a special well-defined band, named the ligamentum cruciatum cruris (O.T. anterior annular ligament, lower band), stretches over the extensor tendons. It has an attachment laterally to the lateral border of the dorsal surface of the calcaneus. It divides into two bands as it passes medially over the dorsum of the foot-a proximal part, which joins the lig. transversum cruris and is attached to the medial malleolus, and a distal part, which passes across the dorsum of the foot, and joins the fascia of the sole at its medial border.

Deep to this liga

ment are three

EXTENSOR HALLUCIS LONGUS
Deep peroneal nerve and
dorsalis pedis artery]

special compart- EXTENSOR DIGITORUM LONGUS

PERONEUS TERTIUS

ments with separate mucous sheaths, one for the tibialis anterior tendon, a second for that of the extensor hallucis longus, and a third for the extensor digitorum longus and peronæus tertius tendons. There are Occasionally other additional bands of the deep fascia passing, like the straps of a sandal, across the dorsum of the foot.

PERONEUS BREVIS-
Peroneal retinaculum.

ABDUCTOR DIGITI QUINTI

Plantar aponeurosis

Lig. transversum cruris.
TIBIALIS ANTERIOR

TIBIALIS POSTERIOR

-Ligamentum
laciniatum

FLEXOR DIGITORUM
LONGUS

-Medial plantar artery

Medial plantar nerve

FLEXOR HALLUCIS LONGUS

ABDUCTOR HALLUCIS

Lateral plantar nerve

Lateral plantar artery
FLEXOR DIGITORUM BREVIS

QUADRATUS PLANTE

FIG. 377.-FRONTAL SECTION THROUGH THE LEFT ANKLE-JOINT, TALUS,
AND CALCANEUS.

The plantar aponeurosis is of great importance. In the centre of the sole it forms a thick triangular band, attached posteriorly to the tuberosity of the calcaneus. It spreads out anteriorly and separates into five slips, which are directed forwards to the bases of the toes. These slips as they separate are joined together by ill-defined bands of transverse fibres, which constitute the superficial transverse metatarsal ligament (fasciculi transversi aponeurosis plantæ). The slip for each toe joins the tissue of the web of the toe and is continuous with the digital sheath. It splits to form a band of fibres directed forwards on each side of the toe to be attached to the sides of the metatarso-phalangeal articulation and the base of the first phalanx.

This central portion of the plantar aponeurosis assists in preserving the arch of the foot, by drawing the toes and the calcaneus together.

On each side it is continuous with a much thinner layer, which covers the lateral and medial muscles of the sole and joins the fascia of the dorsum of the foot at each border. It also gives rise to intermuscular septa, which pass deeply on each side of the flexor digitorum brevis, enclosing that muscle in a separate sheath, and giving investments on either side to the abductor muscles of the great and little toes. At the lateral border of the foot the calcaneo-metatarsal ligament, a thickened band of the fascia, connects the tuberosity of the calcaneus with the base of the fifth metatarsal bone.

The digital sheaths, though smaller, are the same in arrangement as those of the fingers (p. 389). Vaginal ligaments are present in relation to the first and second phalanges.

THE MUSCLES OF THE LEG AND FOOT.

The muscles of the leg and foot are divisible into three series: (1) the extensor muscles on the front of the leg and dorsum of the foot; (2) the peronæi on the lateral aspect of the leg; and (3) the flexor muscles on the back of the leg and in the sole of the foot.

The Muscles on the Front of the Leg and Dorsum of the Foot.

The muscles on the front of the leg and dorsum of the foot include two groups: (1) on the front of the leg, the tibialis anterior, long extensors of the toes and peronæus tertius; and (2) on the dorsum of the foot, the extensor digitorum brevis, and extensor hallucis brevis.

On the front of the leg the tibialis anterior and the extensor digitorum longus and peronæus tertius are superficially placed, and conceal the extensor hallucis longus muscle. On the dorsum of the foot the extensor digitorum brevis muscle lies beneath the tendons of the long extensor of the toes.

M. Tibialis Anterior. The tibialis anterior arises from the lateral condyle and the proximal two-thirds of the lateral surface of the body of the tibia, from the interosseous membrane from the fascia over it, and from an intermuscular septum laterally. The muscle ends in a strong tendon which passes over the dorsum of the foot, to be inserted into a facet on the medial surface of the first cuneiform and the medial side of the base of the first metatarsal bone (Fig. 379, p. 425). Its tendon occupies special compartments beneath both ligamentum transversum and lig. cruciatum cruris, enclosed in a separate, single, mucous sheath.

The tibio-fascialis anterior is a separated portion of the muscle occasionally present, inserted into the fascia on the dorsum of the foot.

Nerve-Supply.-Deep peroneal nerve (L. 4. 5. S. 1.).

Actions. The muscle is a dorsi-flexor of the ankle, and (in combination with the tibialis posterior) it invests the foot.

M. Extensor Digitorum Longus.-The extensor digitorum longus arises, by fleshy fibres, from the lateral side of the lateral condyle of the tibia, from the proximal two-thirds or more of the anterior part of the medial surface of the body of the fibula, from the fascia over it, and from intermuscular septa on either side.

It gives rise to a tendon which passes deep to the ligamentum transversum and cruciatum, and in front of the ankle subdivides into four tendons, inserted into the four lateral toes, exactly in the same way as the corresponding tendons in the hand (see p. 397). They form membranous expansions on the dorsum of the first phalanx, joined by the tendons of the extensor digitorum brevis, lumbricales,

FIG. 379.-MUSCLE-ATTACHMENTS TO LEFT TARSUS AND METATARSUS (Plantar Aspect).

and interossei, each of which separates into one central and two collateral slips, attached respectively to the middle and terminal phalanges. The tendon occupies a separate compartment, along with the peronæus tertius, deep to the ligamentum cruciatum cruris, invested by a special mucous sheath.

Nerve-Supply-Deep peroneal nerve (L. 4. 5. S. 1.).

Actions. A dorsi-flexor of the ankle and an extensor of the four lateral toes.

M. Peronæus Tertius.-The peronæus tertius is a separated portion of the extensor digitorum longus. It is an essentially human muscle. It arises (inseparably from the extensor digitorum longus) from the anterior part of the medial surface of the fibula, and from the inter-muscular septum lateral to it.

The tendon of the muscle is inserted into the dorsal aspect of the base of the fifth metatarsal bone.

Nerve-Supply.-Deep peroneal nerve (L. 4. 5. S. 1.).

Actions. The muscle dorsi-flexes the ankle and raises the lateral border of the foot (as in skating or dancing).

M. Extensor Hallucis Longus.-The extensor hallucis longus arises from

the anterior part of the medial surface of the fibula in its middle three-fifths, medial to the origin of the extensor digitorum longus, and for a corresponding extent from the interosseous membrane. Its tendon passes over the dorsum of the foot, to be inserted into the base of the terminal phalanx of the great toe.

The extensor primi internodii longus and extensor ossis metatarsi hallucis are occasional separate slips of this muscle inserted into the proximal phalanx and the metatarsal bone.

Nerve-Supply.-Deep peroneal nerve (L. 4. 5. S. 1.). Actions. This muscle dorsi-flexes the ankle, and extends the great toe.

EXTENSOR

It usually gives rise to four fleshy bellies, from which narrow tendons are directed forwards and medially, to be inserted into the four medial toes. The three lateral tendons HALLUCIS join those of the long extensor muscle to form the membranous expansions on the dorsum of the toes. The most medial tendon (exLigamen- tensor hallucis brevis) is inserted separately into the base of the first phalanx of the great toe.

LONGUS

tum trans

FIG. 380.-MUSCLES OF THE FRONT OF THE

RIGHT LEG AND DORSUM OF THE RIGHT FOOT.

M. Extensor Digitorum Brevis.-The extensor digitorum brevis arises, on the dorsum of the foot, from a special impression on the dorsal surface of the calcaneus, and from the deep surface of the ligamentum cruciatum cruris.

M. Peronæus Longus.-The peronæus longus arises from the head and the proximal two-thirds of the lateral surface of the body

of the fibula, from intermuscular septa on either side, and from the fascia over it. It forms a stout tendon, which lies superficial to the peronæus brevis, hooks round the lateral malleolus deep to the peroneal retinaculum, crosses the lateral side of the calcaneus, and, passing through a groove on the cuboid bone, is directed across the sole of the foot to be inserted into the lateral sides of the first cuneiform and the